Table des matières
Last updated on: 2020/01/30 03:28
Basic Shell Commands and Text Manipulation Tools
[stextbox id='black' image='null'] To do - You are currently the root user in your terminal. Before proceeding further, type exit and hit the ↵ Enter key. [/stextbox]
Use of Basic Shell Commands
The stty Command
Using this command with the -a switch allows you to identify which combination of keys should be used to control a foreground process:
trainee@ubuntu1604:~$ stty -a speed 38400 baud; rows 26; columns 80; line = 0; intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D; eol = <undef>; eol2 = <undef>; swtch = <undef>; start = ^Q; stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V; discard = ^O; min = 1; time = 0; -parenb -parodd -cmspar cs8 -hupcl -cstopb cread -clocal -crtscts -ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr icrnl ixon -ixoff -iuclc -ixany -imaxbel -iutf8 opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0 tab0 bs0 vt0 ff0 isig icanon iexten echo echoe echok -echonl -noflsh -xcase -tostop -echoprt echoctl echoke -flusho -extproc
[stextbox id='black' image='null'] The two most important combinations are intr = ^C and susp = ^Z. The former kills the process whilst the latter suspends its execution. [/stextbox]
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the stty command to view the command line switches. [/stextbox]
The date command
This command's output gives the current system date and time. The command can also be used to set the system date:
trainee@ubuntu1604:~$ date Fri 30 Sep 15:19:21 CEST 2016
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the date command to view the command line switches. [/stextbox]
The who Command
This command's output shows who is currently connected to the system:
trainee@ubuntu1604:~$ who trainee pts/0 2016-09-29 20:36 (10.0.2.2)
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the who command to view the command line switches. [/stextbox]
The df Command
This command's output shows the free space on each mounted block device:
trainee@ubuntu1604:~$ df Filesystem 1K-blocks Used Available Use% Mounted on udev 230832 0 230832 0% /dev tmpfs 50028 2864 47164 6% /run /dev/sda1 9480420 4269160 4706636 48% / tmpfs 250124 0 250124 0% /dev/shm tmpfs 5120 4 5116 1% /run/lock tmpfs 250124 0 250124 0% /sys/fs/cgroup tmpfs 50028 0 50028 0% /run/user/1000
The units are shown as blocks. In order to humanize the output, it is possible to use the -h switch (also known as a parameter, option or flag):
trainee@ubuntu1604:~$ df -h Filesystem Size Used Avail Use% Mounted on udev 226M 0 226M 0% /dev tmpfs 49M 2.8M 47M 6% /run /dev/sda1 9.1G 4.1G 4.5G 48% / tmpfs 245M 0 245M 0% /dev/shm tmpfs 5.0M 4.0K 5.0M 1% /run/lock tmpfs 245M 0 245M 0% /sys/fs/cgroup tmpfs 49M 0 49M 0% /run/user/1000
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the df command to view the command line switches. [/stextbox]
The free Command
This command's output shows the memory usage:
trainee@ubuntu1604:~$ free
total used free shared buff/cache available
Mem: 500252 88116 8820 1460 403316 387464
Swap: 1997820 10604 1987216
The units are shown as blocks. In order to humanize the output, it is possible to use the -h switch:
trainee@ubuntu1604:~$ free -h
total used free shared buff/cache available
Mem: 488M 86M 8.5M 1.4M 393M 378M
Swap: 1.9G 10M 1.9G
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the free command to view the command line switches. [/stextbox]
The whoami Command
This command's output indicates the user name associated with the current effective user ID:
trainee@ubuntu1604:~$ whoami trainee
Now become the system administrator root:
trainee@ubuntu1604:~$ sudo su - [sudo] password for trainee: trainee root@ubuntu1604:~#
[stextbox id='black' image='null'] Important : Note that the password will not be visible. [/stextbox]
Now use the whoami command again:
root@ubuntu1604:~# whoami root root@ubuntu1604:~#
[stextbox id='black' image='null'] Important : Note the current effective user ID is root. [/stextbox]
Finally execute the exit command to return as trainee:
root@ubuntu1604:~# exit logout trainee@ubuntu1604:~$
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the whoami command to view the command line switches. [/stextbox]
The pwd Command
This command's output shows the current working directory:
trainee@ubuntu1604:~$ pwd /home/trainee
Command Line Switches
[stextbox id='black' image='null'] To do : Use the help command with pwd option to view the command line switches. [/stextbox]
The cd Command
This command's output changes the current working directory to that specified by the argument:
trainee@ubuntu1604:~$ cd /tmp trainee@ubuntu1604:/tmp$ pwd /tmp trainee@ubuntu1604:/tmp$
Command Line Switches
[stextbox id='black' image='null'] To do : Use the help command with cd option to view the command line switches. [/stextbox]
The ls Command
This commands output lists information about the files in directory specified as an argument. If no argument is specified, the output lists the files in the current working directory:
trainee@ubuntu1604:/tmp$ ls hsperfdata_root inode systemd-private-cd33d40e1d3a4e08a9cde3de3603311e-systemd-timesyncd.service-bxC1MJ
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the ls command to view the command line switches. [/stextbox]
The lsof Command
This command's output shows information about open files:
trainee@ubuntu1604:/tmp$ sudo su - [sudo] password for trainee: trainee root@ubuntu1604:~# lsof | more COMMAND PID TID USER FD TYPE DEVICE SIZE/OFF NODE NAME systemd 1 root cwd DIR 8,1 4096 2 / systemd 1 root rtd DIR 8,1 4096 2 / systemd 1 root txt REG 8,1 1577232 325621 /lib/systemd/systemd systemd 1 root mem REG 8,1 18976 266610 /lib/x86_64-linux-gnu/libuuid.so.1.3.0 systemd 1 root mem REG 8,1 262408 266418 /lib/x86_64-linux-gnu/libblkid.so.1.1.0 systemd 1 root mem REG 8,1 14608 266450 /lib/x86_64-linux-gnu/libdl-2.23.so systemd 1 root mem REG 8,1 456632 266555 /lib/x86_64-linux-gnu/libpcre.so.3.13.2 systemd 1 root mem REG 8,1 1864888 266426 /lib/x86_64-linux-gnu/libc-2.23.so systemd 1 root mem REG 8,1 138744 266572 /lib/x86_64-linux-gnu/libpthread-2.23.so systemd 1 root mem REG 8,1 286824 266502 /lib/x86_64-linux-gnu/libmount.so.1.1.0 systemd 1 root mem REG 8,1 64144 266408 /lib/x86_64-linux-gnu/libapparmor.so.1.4.0 systemd 1 root mem REG 8,1 92864 266489 /lib/x86_64-linux-gnu/libkmod.so.2.3.0 systemd 1 root mem REG 8,1 117288 266416 /lib/x86_64-linux-gnu/libaudit.so.1.0.0 systemd 1 root mem REG 8,1 55904 266542 /lib/x86_64-linux-gnu/libpam.so.0.83.1 systemd 1 root mem REG 8,1 252152 266583 /lib/x86_64-linux-gnu/libseccomp.so.2.2.3 systemd 1 root mem REG 8,1 31712 266580 /lib/x86_64-linux-gnu/librt-2.23.so systemd 1 root mem REG 8,1 23128 266429 /lib/x86_64-linux-gnu/libcap.so.2.24 systemd 1 root mem REG 8,1 130224 266584 /lib/x86_64-linux-gnu/libselinux.so.1 systemd 1 root mem REG 8,1 162632 266398 /lib/x86_64-linux-gnu/ld-2.23.so systemd 1 root 0u CHR 1,3 0t0 6 /dev/null systemd 1 root 1u CHR 1,3 0t0 6 /dev/null systemd 1 root 2u CHR 1,3 0t0 6 /dev/null --More--
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the lsof command to view the command line switches. [/stextbox]
The touch Command
This command updates the access and modification times of one or several file(s) to the current time. If the file does not exist, the system creates an empty file:
root@ubuntu1604:~# exit logout trainee@ubuntu1604:/tmp$ touch test trainee@ubuntu1604:/tmp$ ls hsperfdata_root inode systemd-private-cd33d40e1d3a4e08a9cde3de3603311e-systemd-timesyncd.service-bxC1MJ test
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the touch command to view the command line switches. [/stextbox]
The echo Command
This command writes the arguments to the standard output (i.e. the screen):
trainee@ubuntu1604:/tmp$ echo fenestros fenestros
Command Line Switches
[stextbox id='black' image='null'] To do : Use the help command with echo option to view the command line switches. [/stextbox]
The cp Command
This command is used to copy a source to a destination or multiple sources to a directory:
trainee@ubuntu1604:/tmp$ cp test ~ trainee@ubuntu1604:/tmp$ ls -l ~ total 48 drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Desktop drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Documents drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Downloads -rw-r--r-- 1 trainee trainee 8980 mai 3 07:27 examples.desktop drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Music drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Pictures drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Public drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Templates -rw-rw-r-- 1 trainee trainee 0 oct. 4 13:31 test drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Videos -rw-rw-r-- 1 trainee trainee 442 sept. 30 11:35 vitext
[stextbox id='black' image='null'] Note the use of the ~ (tilde) character which is a shortcut to the current user's home directory. In the case of this example : /home/trainee. [/stextbox]
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the cp command to view the command line switches. [/stextbox]
The file Command
This command determines a file type:
trainee@ubuntu1604:/tmp$ file ~/test /home/trainee/test: empty
[stextbox id='black' image='null'] Important - Note that in the case of the first line of the above output, tha command file is incapable of informing you of the type of file since test is empty. [/stextbox]
Using the > key, redirect the output of echo fenestros into the /home/trainee/test file as follows:
trainee@ubuntu1604:/tmp$ echo "fenestros" > ~/test
Now use the file command once again to determine the file type:
trainee@ubuntu1604:/tmp$ file ~/test /home/trainee/test: ASCII text
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the file command to view the command line switches. [/stextbox]
The cat Command
This commands concatenate files, or standard input, to standard output. In the case of only one file as an argument, the effective result is to print the file contents to the screen:
trainee@ubuntu1604:/tmp$ cat ~/test fenestros
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the cat command to view the command line switches. [/stextbox]
The mv Command
This command renames a source to a destination or moves sources to a directory:
trainee@ubuntu1604:/tmp$ mv ~/test . trainee@ubuntu1604:/tmp$ ls -l ~ total 48 drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Desktop drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Documents drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Downloads -rw-r--r-- 1 trainee trainee 8980 mai 3 07:27 examples.desktop drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Music drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Pictures drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Public drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Templates drwxr-xr-x 2 trainee trainee 4096 mai 3 08:03 Videos -rw-rw-r-- 1 trainee trainee 442 sept. 30 11:35 vitext trainee@ubuntu1604:/tmp$ mv test TeSt trainee@ubuntu1604:/tmp$ ls -l total 16 drwxr-xr-x 2 root root 4096 sept. 28 10:34 hsperfdata_root drwxr-xr-x 2 root root 4096 sept. 29 10:32 inode drwx------ 3 root root 4096 sept. 29 10:19 systemd-private-cd33d40e1d3a4e08a9cde3de3603311e-systemd-timesyncd.service-bxC1MJ -rw-rw-r-- 1 trainee trainee 10 oct. 4 13:36 TeSt
[stextbox id='black' image='null'] Note the use of the shortcut . which indicates the current working directory. [/stextbox]
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the mv command to view the command line switches. [/stextbox]
The mkdir Command
This command creates the directory(ies) if it (they) does (do) not exist:
trainee@ubuntu1604:/tmp$ cd ~ trainee@ubuntu1604:~$ mkdir testdir trainee@ubuntu1604:~$ ls Desktop Downloads Music Public testdir vitext Documents examples.desktop Pictures Templates Videos
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the mkdir command to view the command line switches. [/stextbox]
The rmdir Command
This command removes the directory(ies) if it (they) is (are) empty:
trainee@ubuntu1604:~$ rmdir testdir trainee@ubuntu1604:~$ ls Desktop Downloads Music Public Videos Documents examples.desktop Pictures Templates vitext
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the rmdir command to view the command line switches. [/stextbox]
The rm Command
This command removes a directory, empty of not, as well as files:
trainee@ubuntu1604:~$ mkdir testdir1 trainee@ubuntu1604:~$ cd /tmp trainee@ubuntu1604:/tmp$ echo "fenestros" > TeSt trainee@ubuntu1604:/tmp$ cd ~ trainee@ubuntu1604:~$ mv /tmp/TeSt ~/testdir1 trainee@ubuntu1604:~$ ls -lR testdir1/ testdir1/: total 4 -rw-rw-r-- 1 trainee trainee 10 oct. 4 14:17 TeSt trainee@ubuntu1604:~$ rmdir testdir1/ rmdir: failed to remove 'testdir1/': Directory not empty trainee@ubuntu1604:~$ rm -rf testdir1/ trainee@ubuntu1604:~$ ls Desktop Downloads Music Public Videos Documents examples.desktop Pictures Templates vitext
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the rm command to view the command line switches. [/stextbox]
The sort Command
This command writes a sorted concatenation of all files to standard output:
trainee@ubuntu1604:~$ touch aac abc bca xyz trainee@ubuntu1604:~$ ls aac bca Documents examples.desktop Pictures Templates vitext abc Desktop Downloads Music Public Videos xyz trainee@ubuntu1604:~$ ls | sort aac abc bca Desktop Documents Downloads examples.desktop Music Pictures Public Templates Videos vitext xyz trainee@ubuntu1604:~$ ls | sort -r xyz vitext Videos Templates Public Pictures Music examples.desktop Downloads Documents Desktop bca abc aac
[stextbox id='black' image='null'] Important - Note the use of the | character, called a pipe. A pipe is used to channel the standard output of the command that precedes it into the standard input of the command that follows it. [/stextbox]
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the sort command to view the command line switches. [/stextbox]
The more Command
This command is used to display a long file page by page:
trainee@ubuntu1604:~$ more /etc/services # Network services, Internet style # # Note that it is presently the policy of IANA to assign a single well-known # port number for both TCP and UDP; hence, officially ports have two entries # even if the protocol doesn't support UDP operations. # # Updated from http://www.iana.org/assignments/port-numbers and other # sources like http://www.freebsd.org/cgi/cvsweb.cgi/src/etc/services . # New ports will be added on request if they have been officially assigned # by IANA and used in the real-world or are needed by a debian package. # If you need a huge list of used numbers please install the nmap package. tcpmux 1/tcp # TCP port service multiplexer echo 7/tcp echo 7/udp discard 9/tcp sink null discard 9/udp sink null systat 11/tcp users daytime 13/tcp daytime 13/udp netstat 15/tcp qotd 17/tcp quote msp 18/tcp # message send protocol --More--(4%)
[stextbox id='black' image='null'] Important - The ↵ Enter key scrolls down line by line, the Space Bar key scrolls down page by page and the Q key comes back to the command line prompt. [/stextbox]
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the more command to view the command line switches. [/stextbox]
The less Command
The less command produces a similar result to that of the more command. Practice using the less command and refer to the help using less –help. Which command seems the most powerful and versatile ?
trainee@ubuntu1604:~$ less /etc/services # Network services, Internet style # # Note that it is presently the policy of IANA to assign a single well-known # port number for both TCP and UDP; hence, officially ports have two entries # even if the protocol doesn't support UDP operations. # # Updated from http://www.iana.org/assignments/port-numbers and other # sources like http://www.freebsd.org/cgi/cvsweb.cgi/src/etc/services . # New ports will be added on request if they have been officially assigned # by IANA and used in the real-world or are needed by a debian package. # If you need a huge list of used numbers please install the nmap package. tcpmux 1/tcp # TCP port service multiplexer echo 7/tcp echo 7/udp discard 9/tcp sink null discard 9/udp sink null systat 11/tcp users daytime 13/tcp daytime 13/udp netstat 15/tcp qotd 17/tcp quote msp 18/tcp # message send protocol /etc/services
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the less command to view the command line switches. [/stextbox]
The find Command
This command is used to search for a specific file or directory. The default path is the current directory and default expression is -print:
trainee@ubuntu1604:~$ find acc find: ‘acc’: No such file or directory trainee@ubuntu1604:~$ find aac aac
[stextbox id='black' image='null'] Important : Note that when the file cannot be found, the find command informs you clearly. However when the file is found, the find command just prints the name of the file to standard output. [/stextbox]
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the find command to view the command line switches. [/stextbox]
The su Command
This command is used to change the effective user id and group id to that of the user passed as an argument. When executed with no argument, the system assumes the destination user is root:
trainee@ubuntu1604:~$ sudo su - [sudo] password for trainee: trainee
[stextbox id='black' image='null'] Important : Note that the password will not be visible. [/stextbox]
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the su command to view the command line switches. [/stextbox]
The updatedb and locate Commands
The locate command is used to list files in databases that match a pattern supplied as an argument to the command. The locate command uses a database. This database needs to be created using the updatedb command before using the locate command.
The default database is /var/lib/mlocate/mlocate.db:
root@ubuntu1604:~# ls -l /var/lib/mlocate/mlocate.db -rw-r----- 1 root mlocate 5293946 oct. 2 07:35 /var/lib/mlocate/mlocate.db
[stextbox id='black' image='null'] Important : For information concerning the database format, please see man 5 locatedb. [/stextbox]
The updatedb command is configured by editing the /etc/updatedb.conf file:
root@ubuntu1604:~# cat /etc/updatedb.conf PRUNE_BIND_MOUNTS="yes" # PRUNENAMES=".git .bzr .hg .svn" PRUNEPATHS="/tmp /var/spool /media /home/.ecryptfs /var/lib/schroot" PRUNEFS="NFS nfs nfs4 rpc_pipefs afs binfmt_misc proc smbfs autofs iso9660 ncpfs coda devpts ftpfs devfs mfs shfs sysfs cifs lustre tmpfs usbfs udf fuse.glusterfs fuse.sshfs curlftpfs ecryptfs fusesmb devtmpfs"
Use of these two commands is very simple:
root@ubuntu1604:~# updatedb root@ubuntu1604:~# locate aac /home/trainee/aac /lib/modules/4.4.0-21-generic/kernel/drivers/scsi/aacraid /lib/modules/4.4.0-21-generic/kernel/drivers/scsi/aacraid/aacraid.ko /lib/modules/4.4.0-38-generic/kernel/drivers/scsi/aacraid /lib/modules/4.4.0-38-generic/kernel/drivers/scsi/aacraid/aacraid.ko /usr/share/app-install/desktop/krita-data:kde4__calligraactive.desktop /usr/share/mime/audio/aac.xml /usr/src/linux-headers-4.4.0-21/drivers/scsi/aacraid /usr/src/linux-headers-4.4.0-21/drivers/scsi/aacraid/Makefile /usr/src/linux-headers-4.4.0-21-generic/include/config/scsi/aacraid.h /usr/src/linux-headers-4.4.0-38/drivers/scsi/aacraid /usr/src/linux-headers-4.4.0-38/drivers/scsi/aacraid/Makefile /usr/src/linux-headers-4.4.0-38-generic/include/config/scsi/aacraid.h
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the updatedb and locate commands to view their command line switches. [/stextbox]
The whereis Command
This command is used to show the full paths of the executable, the configuration files and the manuals associated with the argument:
root@ubuntu1604:~# whereis passwd passwd: /usr/bin/passwd /etc/passwd /usr/share/man/man5/passwd.5.gz /usr/share/man/man1/passwd.1.gz /usr/share/man/man1/passwd.1ssl.gz
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the whereis command to view the command line switches. [/stextbox]
The which Command
This command searches the PATH variable and returns to standard output the first full path associated with the argument:
root@ubuntu1604:~# which passwd /usr/bin/passwd
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the which command to view the command line switches. [/stextbox]
The uptime Command
This command prints to standard output the current time, the length of time the system has been up, the number of users on the system and the average number of jobs in the run queue over the last 1, 5 and 15 minutes:
root@ubuntu1604:~# uptime 15:18:02 up 1 day, 13:10, 1 user, load average: 0,00, 0,03, 0,0
Command Line Switches
The switches associated with this command are:
[stextbox id='black' image='null'] To do : Use the –help option of the uptime command to view the command line switches. [/stextbox]
The w Command
This command outputs the same data as the uptime command on the first line and then complements this information with the details of each user connected to the system, including what each user is currently doing. This is the replacement under Linux for the Unix command whodo:
root@ubuntu1604:~# w 15:27:17 up 1 day, 13:19, 1 user, load average: 0,10, 0,06, 0,06 USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT trainee pts/0 10.0.2.2 lun.17 0.00s 0.11s 0.00s sshd: trainee [priv]
The JCPU time is the time used by all processes attached to the tty. It does not include past background jobs, but does include currently running background jobs.
The PCPU time is the time used by the current process, named in the what field.
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the w command to view the command line switches. [/stextbox]
The uname Command
This command prints system information to the standard output:
root@ubuntu1604:~# uname -a Linux ubuntu1604 4.4.0-21-generic #37-Ubuntu SMP Mon Apr 18 18:33:37 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux root@ubuntu1604:~# uname -s Linux root@ubuntu1604:~# uname -n ubuntu1604 root@ubuntu1604:~# uname -r 4.4.0-21-generic root@ubuntu1604:~# uname -v #37-Ubuntu SMP Mon Apr 18 18:33:37 UTC 2016 root@ubuntu1604:~# uname -m x86_64 root@ubuntu1604:~# uname -p x86_64 root@ubuntu1604:~# uname -i x86_64 root@ubuntu1604:~# uname -o GNU/Linux
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the uname command to view the command line switches. [/stextbox]
The du Command
This command summarizes disk usage of each file, recursively for directories:
root@ubuntu1604:~# du -sh /* 2>/dev/null 13M /bin 100M /boot 4,0K /cdrom 0 /dev 13M /etc 1,7M /home 0 /initrd.img 0 /initrd.img.old 584M /lib 4,0K /lib64 16K /lost+found 4,0K /media 4,0K /mnt 155M /opt 0 /proc 6,1M /root 4,1M /run 13M /sbin 4,0K /snap 4,0K /srv 0 /sys 72K /tmp 2,9G /usr 341M /var 0 /vmlinuz 0 /vmlinuz.old
[stextbox id='black' image='null'] Important : Note the use of the 2>/dev/null redirection. This sends all eventual errors in the file descriptor 2 directly to /dev/null so that they do not appear in the output. File descriptors are covered in the The Command Line Interface unit. [/stextbox]
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the du command to view the command line switches. [/stextbox]
The clear Command
This command is used to clear the current screen of the terminal:
root@ubuntu1604:~# clear root@ubuntu1604:~#
The exit Command
This command exits the current shell:
root@ubuntu1604:~# exit logout trainee@ubuntu1604:~$
Command Line Switches
[stextbox id='black' image='null'] To do : Use the help command with exit option to view the command line switches. [/stextbox]
The logout Command
This command logs out a user from a login shell writing the utmp and wtmp entries in the log files.
Command Line Switches
[stextbox id='black' image='null'] To do : Use the help command with logout option to view the command line switches. [/stextbox]
The sleep Command
This command pauses for a number seconds. The number is specified as the first argument.
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the sleep command to view the command line switches. [/stextbox]
The wall Command
The wall command displays a message, or the contents of a file, or otherwise its standard input, on the terminals of all currently logged in users.The command will wrap lines that are longer than 79 characters. Short lines are whitespace padded to have 79 characters. The command will always put a carriage return and new line at the end of each line. Only the superuser can write on the terminals of users who have chosen to deny messages or are using a program which automatically denies messages. Reading from a file is refused when the invoker is not superuser and the program is suid or sgid.
Start a second session as trainee via ssh on your VM. Return to your first session as root and type :
trainee@ubuntu1604:~$ sudo su -
[sudo] password for trainee: trainee
root@ubuntu1604:~# wall this is a message from root
Broadcast message from trainee@ubuntu1604 (pts/0) (Fri Oct 7 10:18:21 2016):
this is a message from root
root@ubuntu1604:~#
In the second session you should see the following message :
Broadcast message from trainee@ubuntu1604 (pts/0) (Fri Oct 7 10:18:21 2016):
this is a message from root
The seq Command
The seq command prints numbers from FIRST to LAST, in steps of INCREMENT:
- seq [OPTION]… LAST
- seq [OPTION]… FIRST LAST
- seq [OPTION]… FIRST INCREMENT LAST
For example :
root@ubuntu1604:~# seq 10 1 2 3 4 5 6 7 8 9 10 root@ubuntu1604:~# seq 20 30 20 21 22 23 24 25 26 27 28 29 30 root@ubuntu1604:~# seq 20 10 90 20 30 40 50 60 70 80 90 root@ubuntu1604:~#
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the seq command to view the command line switches. [/stextbox]
The screen Command
Screen is a full-screen window manager that multiplexes a physical terminal between several processes (typically interactive shells). Each virtual terminal provides the functions of a DEC VT100 terminal and, in addition, several control functions from the ISO 6429 (ECMA 48, ANSI X3.64) and ISO 2022 standards (e.g. insert/delete line and support for multiple character sets). There is a scrollback history buffer for each virtual terminal and a copy-and-paste mechanism that allows moving text regions between windows.
The screen command is not installed by default under Ubuntu 16.04 LTS. Use the apt-get to install it:
root@ubuntu1604:~# which screen root@ubuntu1604:~# apt-get install screen Reading package lists... Done Building dependency tree Reading state information... Done The following packages were automatically installed and are no longer required: libpango1.0-0 libpangox-1.0-0 Use 'apt autoremove' to remove them. Suggested packages: iselect | screenie | byobu The following NEW packages will be installed: screen 0 upgraded, 1 newly installed, 0 to remove and 1 not upgraded. Need to get 560 kB of archives. After this operation, 972 kB of additional disk space will be used. Get:1 http://fr.archive.ubuntu.com/ubuntu xenial/main amd64 screen amd64 4.3.1-2build1 [560 kB] Fetched 560 kB in 0s (2 306 kB/s) Selecting previously unselected package screen. (Reading database ... 207619 files and directories currently installed.) Preparing to unpack .../screen_4.3.1-2build1_amd64.deb ... Unpacking screen (4.3.1-2build1) ... Processing triggers for systemd (229-4ubuntu10) ... Processing triggers for ureadahead (0.100.0-19) ... Processing triggers for install-info (6.1.0.dfsg.1-5) ... Processing triggers for man-db (2.7.5-1) ... Setting up screen (4.3.1-2build1) ... Processing triggers for systemd (229-4ubuntu10) ... Processing triggers for ureadahead (0.100.0-19) ... root@ubuntu1604:~# which screen /usr/bin/screen
Create a session with screen:
root@ubuntu1604:~# screen -S mysession
Now press the CTRL and A keys, release the A key and press the C key in order to create a second nested screen.
To return to the first screen, use the CTRL A A keys. This allows you to toggle between the last two screens used.
To see the status of all active screens, use the screen -ls command:
root@ubuntu1604:~# screen -ls
There is a screen on:
1745.mysession (07/10/2016 11:00:55) (Attached)
1 Socket in /var/run/screen/S-root
Now enter the following commands:
root@ubuntu1604:~# sleep 9999 & [1] 9699 root@ubuntu1604:~# jobs [1]+ Running sleep 9999 & root@ubuntu1604:~#
In order to detach the current screen press the CTRL and A keys, release the A key and press the D key:
root@ubuntu1604:~# screen -S mysession [detached from 1745.mysession] root@ubuntu1604:~#
To re-attach the screen, execute the following command:
root@ubuntu1604:~# screen -r
Using the jobs command, check if the process created by the sleep command is still running:unit
root@ubuntu1604:~# jobs [1]+ Running sleep 9999 &
To move forward or backwards between screens press the CTRL and A keys, release the A key and press the N key or press the CTRL and A keys, release the A key and press the P key.
Once again detach the current screen by pressing the CTRL A keys, releasing the A key and then pressing D:
root@ubuntu1604:~# screen -S mysession [detached from 1745.mysession] root@ubuntu1604:~#
Now create a new, non-nested screen:
root@ubuntu1604:~# screen -S mysession1
Use the screen -ls command to see what has happened:
root@ubuntu1604:~# screen -ls
There are screens on:
15800.mysession1 (07/10/2016 13:58:29) (Attached)
1745.mysession (07/10/2016 11:00:55) (Detached)
2 Sockets in /var/run/screen/S-root.
To re-attach a specific screen, reference it by it's number:
root@ubuntu1604:~# screen -r 1745
Finally, check out what has happened:
root@ubuntu1604:~# sleep 9999 &
[1] 9699
root@ubuntu1604:~# jobs
[1]+ Running sleep 9999 &
root@ubuntu1604:~# jobs
[1]+ Running sleep 9999 &
root@ubuntu1604:~# screen -ls
There are screens on:
15800.mysession1 (07/10/2016 13:58:29) (Attached)
1745.mysession (07/10/2016 11:00:55) (Attached)
2 Sockets in /var/run/screen/S-root.
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the screen command to view the command line switches. [/stextbox]
Switches and Arguments
Switches under Linux can either be short or long. Several differences are important to note.
Firstly short options are generally preceded by a single dash -, whilst long options are preceded by a double dash - -.
An example is the help option used with most commands:
- -h
- –help
Secondly, Linux short switches can be combined whereas long switches cannot be combined. For example ls -l -a -i can also be written as ls -lai, ls -lia or ls -ali:
root@ubuntu1604:~# ls -lai /tmp
total 40
390918 drwxrwxrwt 10 root root 4096 oct. 7 16:31 .
2 drwxr-xr-x 24 root root 4096 sept. 28 10:40 ..
521792 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .font-unix
522570 drwxr-xr-x 2 root root 4096 sept. 28 10:34 hsperfdata_root
521777 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .ICE-unix
521308 drwxr-xr-x 2 root root 4096 sept. 29 10:32 inode
395765 srw------- 1 root root 0 sept. 28 10:34 .java_pid2124
521306 drwx------ 3 root root 4096 sept. 29 10:19 systemd-private-cd33d40e1d3a4e08a9cde3de3603311e-systemd-timesyncd.service-bxC1MJ
521801 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .Test-unix
521757 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .X11-unix
521785 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .XIM-unix
root@ubuntu1604:~# ls -ali /tmp
total 40
390918 drwxrwxrwt 10 root root 4096 oct. 7 16:31 .
2 drwxr-xr-x 24 root root 4096 sept. 28 10:40 ..
521792 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .font-unix
522570 drwxr-xr-x 2 root root 4096 sept. 28 10:34 hsperfdata_root
521777 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .ICE-unix
521308 drwxr-xr-x 2 root root 4096 sept. 29 10:32 inode
395765 srw------- 1 root root 0 sept. 28 10:34 .java_pid2124
521306 drwx------ 3 root root 4096 sept. 29 10:19 systemd-private-cd33d40e1d3a4e08a9cde3de3603311e-systemd-timesyncd.service-bxC1MJ
521801 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .Test-unix
521757 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .X11-unix
521785 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .XIM-unix
However ls -l –all –inode cannot be written ls -l –allinode:
root@ubuntu1604:~# ls -l --all --inode /tmp
total 40
390918 drwxrwxrwt 10 root root 4096 oct. 7 16:31 .
2 drwxr-xr-x 24 root root 4096 sept. 28 10:40 ..
521792 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .font-unix
522570 drwxr-xr-x 2 root root 4096 sept. 28 10:34 hsperfdata_root
521777 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .ICE-unix
521308 drwxr-xr-x 2 root root 4096 sept. 29 10:32 inode
395765 srw------- 1 root root 0 sept. 28 10:34 .java_pid2124
521306 drwx------ 3 root root 4096 sept. 29 10:19 systemd-private-cd33d40e1d3a4e08a9cde3de3603311e-systemd-timesyncd.service-bxC1MJ
521801 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .Test-unix
521757 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .X11-unix
521785 drwxrwxrwt 2 root root 4096 sept. 28 10:31 .XIM-unix
root@ubuntu1604:~# ls -l --allinode /tmp
ls: unrecognized option '--allinode'
Try 'ls --help' for more information.
[stextbox id='black' image='null'] Important - You should not combine any short options that take an argument. [/stextbox]
Manipulating Text Files
Text files play a very important role under Linux. For example, almost all configuration files are simple text files and being able to manipulate them is of great importance. Manipulating text files is essentially achieved by using Regular Expressions. There are two types of Regular Expressions:
- The IEEE POSIX Basic Regular Expressions (BRE) understood by the commands vi, grep, expr and sed,
- The IEEE POSIX Extended Regular Expressions (ERE) understood by the commands egrep ( grep -E ) and awk.
Regular Expressions
Regular Expressions use Metacharacters. Certain are common to both BREs and EREs:
| Metacharacter | Description |
|---|---|
| ^string | Match lines beginning with string |
| string$ | Match lines ending with string |
| \Metacharacter | Cancel any special effect associated with Metacharacter |
| [string] | Match any of the characters within string |
| [^string] | Exclude any of the characters in string |
| . | Match any character except when at the end of a line |
| character* | Match 0 or more occurrences of character |
| \< | Match string at the beginning of a word |
| \> | Match string at the end of a word |
BREs
Certain Metacharacters are specific to BREs:
| Metacharacter | Description |
|---|---|
| \{x,y\} | Match from x to y occurrences of the preceeding element |
| \{x\} | Match exactly x occurrences of the preceeding element |
| \{x,\} | Match x or more occurrences of the preceeding element |
| \(BRE) | Commit to memory the BRE |
| \1 | Recall the first BRE committed to memory |
| \2, \3 … | Recall the second BRE committed to memory, recall the third BRE committed to memory … |
EREs
Certain Metacharacters are specific to EREs:
| Metacharacter | Description |
|---|---|
| {x,y} | Match from x to y occurrences of the preceeding element |
| {x} | Match exactly x occurrences of the preceeding element |
| {x,} | |
| ? | Matches 0 or 1 occurrence of the preceeding element |
| + | Matches 1 or more occurrence(s) of the preceeding element |
| | | Matches either the expression before or the expression after the operator |
| () | Combines the Reguler Expressions between the parentheses |
Text-search Utilities
The grep Command
The grep command can be used to find lines containing a string of characters in a group of files. The -v or –invert-case option can be stipulated to find lines that do not contain the specified string.
The grep command is case sensitive. The -i or –ignore-case option can be specified in order to use grep in a non case sensitive search.
The grep command can also use BREs.
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the grep command to view the command line switches. [/stextbox]
The egrep Command
The egrep command is identical to the grep command when used with the -E switch. Both can use EREs.
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the egrep command to view the command line switches. [/stextbox]
The fgrep Command
The fgrep command is identical to the grep command when used with the -F switch. Both have no knowledge of Regular Expressions.
[stextbox id='black' image='null'] To do : Use the –help option of the fgrep command to view the command line switches. [/stextbox]
LAB #1 - Using grep, egrep and fgrep
Download the following file by clicking on it's title:
- greptest
fenestrOS fenestros 555-5555 f .fenestros .fe £
Move the file to the /tmp directory:
root@ubuntu1604:~# mv /home/trainee/Downloads/greptest /tmp/greptest
Now use grep to search for lines containing at least one uppercase or lowercase letter:
root@ubuntu1604:~# grep '[a-zA-Z]' /tmp/greptest fenestrOS fenestros f .fenestros .fe
Next use grep to search for lines containing at least one uppercase or lowercase letter or a number:
root@ubuntu1604:~# grep '[a-zA-Z0-9]' /tmp/greptest fenestrOS fenestros 555-5555 f .fenestros .fe
To search for the NNN-NNNN pattern where N is a number, use the following command:
root@ubuntu1604:~# grep '[0-9]\{3\}-[0-9]\{4\}' /tmp/greptest
555-5555
Lines containing just one character have that character both at the beginning (^) and at the end ($) of the line:
root@ubuntu1604:~# grep '^.$' /tmp/greptest f £
To search for a line containing a special character such as ., that character needs to be preceded by \:
root@ubuntu1604:~# grep '^\.' /tmp/greptest .fenestros .fe
[stextbox id='black' image='null'] Important - The grep command can also be used to search for a string in all the files within a specific directory as follows grep -rnw 'directory' -e “pattern”. You can also search only within certain files by specifying the files extensions: grep –include={*.doc,*.xls} -rnw 'directory' -e “pattern”. Finally you can exclude certain file extensions as follows: grep –exclude=*.doc -rnw 'directory' -e “pattern”. [/stextbox]
Download the following file by clicking on it's title:
- greptest
# Starting comment fenestrOS fenestros # Another comment 555-5555 f .fenestros .fe £ # End comment
Move the file to the /tmp directory:
root@ubuntu1604:~# mv /home/trainee/Downloads/greptest /tmp/greptest
Now use the grep command with the -E switch to remove all the comments and empty lines:
root@ubuntu1604:~# grep -E -v '^(#|$)' /tmp/greptest fenestrOS fenestros 555-5555 f .fenestros .fe £
[stextbox id='black' image='null'] The expression '^(#|$)' matches all lines beginning with the # character OR all lines with zero characters between the start and the end of the line. [/stextbox]
Now use the egrep command to do the same thing, this time redirecting the output to the file /tmp/greptest1:
root@ubuntu1604:~# egrep -v '^(#|$)' /tmp/greptest > /tmp/greptest1 root@ubuntu1604:~# cat /tmp/greptest1 fenestrOS fenestros 555-5555 f .fenestros .fe £
[stextbox id='black' image='null'] Important: The above command is very useful when you want to quickly ascertain which directives are active in a very long configuration file. [/stextbox]
Download the following file by clicking on it's title:
- greptest
# Starting comment ^ This line will be used to demonstrate the use of fgrep fenestrOS fenestros # Another comment 555-5555 f .fenestros .fe £ # End comment
Move the file to the /tmp directory:
root@ubuntu1604:~# mv /home/trainee/Downloads/greptest /tmp/greptest
Now use fgrep to match the line starting with the ^ character:
root@ubuntu1604:~# fgrep '^' /tmp/greptest ^ This line will be used to demonstrate the use of fgrep
Compare the above output to that when using the grep command:
root@ubuntu1604:~# grep '^' /tmp/greptest # Starting comment ^ This line will be used to demonstrate the use of fgrep fenestrOS fenestros # Another comment 555-5555 f .fenestros .fe £ # End comment
As you can see, grep matched every line that had a beginning. In order to get the same result as the grep command, you need to use the following command:
root@ubuntu1604:~# grep '^\^' /tmp/greptest ^ This line will be used to demonstrate the use of fgrep
The Stream EDitor SED
sed is an abbreviation of Stream EDitor and is a non-interactive text editor. sed's basic syntax is as follows:
sed [address] command [arguments] file
The specified commands are applied to each line in the file unless an address is specified. Sed prints all results to standard output and does not modify the source file. The address therefore specifies which lines are concerned by the command.
sed's addresses are as follows:
| address | Matching lines |
|---|---|
| x | Line number x |
| $ | The last line of the file |
| /BRE/ | Lines matching the specified BRE |
| x,y | From line x to line y |
| /ERb1/, /ERb2/ | All lines from the first line that matches the first BRE to the first line that matches the second BRE |
sed's commands are as follows:
| command | Description |
|---|---|
| d | Do not show the matching line(s) on standard output |
| p | Show the matching line(s) on standard output |
| s | Do a substitution upon match |
| w | Write the matching line(s) to a file |
| = | Print the matching line's number |
| ! | Exclude the line(s) matching the address |
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the fgrep command to view the command line switches. [/stextbox]
LAB #2 - Using sed
Start by displaying the contents of the file /etc/services whilst inhibiting the display of the first 10 lines:
root@ubuntu1604:~# sed '1,10d' /etc/services | more # If you need a huge list of used numbers please install the nmap package. tcpmux 1/tcp # TCP port service multiplexer echo 7/tcp echo 7/udp discard 9/tcp sink null discard 9/udp sink null systat 11/tcp users daytime 13/tcp daytime 13/udp netstat 15/tcp qotd 17/tcp quote msp 18/tcp # message send protocol msp 18/udp chargen 19/tcp ttytst source chargen 19/udp ttytst source ftp-data 20/tcp ftp 21/tcp fsp 21/udp fspd ssh 22/tcp # SSH Remote Login Protocol ssh 22/udp telnet 23/tcp smtp 25/tcp mail --More--
Now display the same file without any commented lines:
root@ubuntu1604:~# sed '/^#/d' /etc/services | more tcpmux 1/tcp # TCP port service multiplexer echo 7/tcp echo 7/udp discard 9/tcp sink null discard 9/udp sink null systat 11/tcp users daytime 13/tcp daytime 13/udp netstat 15/tcp qotd 17/tcp quote msp 18/tcp # message send protocol msp 18/udp chargen 19/tcp ttytst source chargen 19/udp ttytst source ftp-data 20/tcp ftp 21/tcp fsp 21/udp fspd ssh 22/tcp # SSH Remote Login Protocol ssh 22/udp telnet 23/tcp smtp 25/tcp mail time 37/tcp timserver --More--
[stextbox id='black' image='null'] Important: Note that the BRE is preceeded and followed by the / character. [/stextbox]
Continue by trying to just display the first two lines of /etc/passwd:
root@ubuntu1604:~# sed '1,2p' /etc/passwd root:x:0:0:root:/root:/bin/bash root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/nologin sync:x:4:65534:sync:/bin:/bin/sync ...
[stextbox id='black' image='null'] Important: As you can see in the above output, the command used displays not only the first two lines but also the entire file. As a result the first two lines are displayed twice. [/stextbox]
To force sed to only display the lines you specify, use the -n switch:
root@ubuntu1604:~# sed -n '1,2p' /etc/passwd root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
Now you want to use sed to strip out the comments from /etc/services and save the result to /tmp/sedtest without displaying anything on standard output:
root@ubuntu1604:~# sed -n '/^#/!w /tmp/sedtest' /etc/services root@ubuntu1604:~# more /tmp/sedtest tcpmux 1/tcp # TCP port service multiplexer echo 7/tcp echo 7/udp discard 9/tcp sink null discard 9/udp sink null systat 11/tcp users daytime 13/tcp daytime 13/udp netstat 15/tcp qotd 17/tcp quote msp 18/tcp # message send protocol msp 18/udp chargen 19/tcp ttytst source chargen 19/udp ttytst source ftp-data 20/tcp ftp 21/tcp fsp 21/udp fspd ssh 22/tcp # SSH Remote Login Protocol ssh 22/udp telnet 23/tcp smtp 25/tcp mail time 37/tcp timserver --More--(2%)
[stextbox id='black' image='null'] Important: In the above command, we start by matching all lines in the /etc/services file that start with a #. We then tell sed to write all non-matching lines to the file /tmp/sedtest. [/stextbox]
Finally, create a file containing user1,user2,user3. Replace the commas by spaces:
root@ubuntu1604:~# echo "user1,user2,user3" > /tmp/sedtest1 root@ubuntu1604:~# cat /tmp/sedtest1 | sed 's/,/ /g' user1 user2 user3
[stextbox id='black' image='null'] Important: The above sed command has the following format s/what is to be replaced (character, string or BRE)/replacement/g. The use of the g character forces sed to replace all occurences that match. If g is not stipulated, only the first matching occurence is replaced. [/stextbox]
The Text Processor AWK
Presentation
The awk command acts as a filter and uses the following syntax:
awk [-F seperator] '[condition] {action}' [file]
Field Separation
A file or a text stream is treated by awk as a sequence of records. By default each line is a record. Awk analyzes each record, separating that record into fields and then storing the record and fields in variables:
- $0 contains the record,
- $1 contains the first field,
- $2 contains the second field,
- e.t.c.
Awk interprets a space as a separator between fields unless a different separator is specified with the -F option.
Awk then checks if the condition is met for each record and if so, executes the action.
For example, the following command takes the standard output of ls -l and prints fields 8, 3 and 4 to standard output:
root@ubuntu1604:~# ls -l | awk '{print $8 $3 $4}'
10:40rootroot
2016rootroot
2016rootroot
Since there is no condition, the action is applied to every record.
To make the output easier to read, you can include spaces between each field:
root@ubuntu1604:~# ls -l | awk '{print $8 " " $3 " " $4}'
10:40 root root
2016 root root
2016 root root
Conditions
A regular expression applied to a record
- Format:
- /regular expression/ {action}
- Exemple:
- /hello/ {print $0}
A regular expression applied to a field
- Format:
- $n ~/regular expression/ {action}
- $n!~/regular expression/ {action}
- Examples:
- $1 ~/hello/ {print $0}
- $1!~/hello/ {print $0}
Comparisons
- Format:
- $n operator criteria {action}
- Example:
- $1 > 20 {print $0}
Operators
| Operator | Condition |
|---|---|
| < | Less than |
| ⇐ | Less than or equal to |
| == | Equal to |
| != | Different |
| > | Greater than |
| >= | Greater than or equal to |
Logical Operators
- Format:
- test1 logical operator test2 {action}
- Example:
- $1 ~/hello/ && $2 > 20 {print $0}
Operators
| Operator | Condition |
|---|---|
| || | OR |
| && | AND |
| ! | NO |
Built-in Variables
- Format:
- expression1, expression2 {instruction}
- Example:
- NR==7, NR==10 {print $0}
Variables
| Variable | Description |
|---|---|
| NR | Total number of records |
| NF | Total number of fields |
| FILENAME | Name of current input file |
| FS | The field separator, by default a space or tab |
| RS | The record separator, by default newline |
| OFS | Output field separator, by default a space |
| ORS | Output record separator, by default newline |
| OFMT | Numeric output format, by default“%.6g” |
Awk Scripts
To combine several clauses composed of conditions and actions in the same statement, it is advisable to create an awk script. Awk scripts are comprised of three sections:
- BEGIN
- This section is executed once, prior to executing the body of the script
- BODY
- This sections contains the clauses to be applied to each line
- END
- This section is executed once, after executing the body of the script
For example:
root@ubuntu1604:~# cat > awkscript
BEGIN {
print "List of the currently mounted file systems"}
{print $0}
END {
print "=========================================="}
[^D]
Now apply the awk script to /etc/fstab :
root@ubuntu1604:~# awk -f awkscript /etc/fstab List of the currently mounted file systems # /etc/fstab: static file system information. # # Use 'blkid' to print the universally unique identifier for a # device; this may be used with UUID= as a more robust way to name devices # that works even if disks are added and removed. See fstab(5). # # <file system> <mount point> <type> <options> <dump> <pass> # / was on /dev/sda1 during installation UUID=c27fce7f-cc8a-4c6f-b19b-d929a4d570f2 / ext4 errors=remount-ro 0 1 # swap was on /dev/sda5 during installation UUID=68f67549-63f1-4833-b792-3566455bbe95 none swap sw 0 0 ==========================================
[stextbox id='black' image='null'] Important: Note the use of the -f switch which instructs awk to use the script. [/stextbox]
The printf function
The integrated function printf is used to format output and has the following syntax:
printf ("string",expression1,expression2,...,expressionn)
string contains as many formats as there are expressions.
Examples of formats commonly used are:
| Format | Description |
|---|---|
| %30s | Displays a right-justified string of 30 characters |
| %-30s | Displays a left-justified string of 30 characters |
| %4d | Displays a right-justified decimal number of 4 digits |
| %-4d | Displays a left-justified decimal number of 4 digits |
Control Statements
awk can use the following control statements:
if
if condition {
command
command
...
}
else {
command
command
...
}
or:
if condition
command
else
command
for
for variable in list {
command
command
...
}
or:
for variable in list
command
or in the case of a table:
for key in table {
print key , table[key]
}
while
while condition {
command
command
...
}
do-while
do {
command
command
...
} while condition
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the awk command to view the command line switches. [/stextbox]
LAB #3 - Using awk
Download the file sales.txt by clicking on the title below:
- sales.txt
# FenestrOs.com # Annual sales by French department # 83 Desktops§100 Portables§50 Servers§21 Ipads§4 # 06 Desktops§99 Portables§60 Servers§8 Ipads§16 # 13 Desktops§130 Portables§65 Servers§12 Ipads§56
Now download the awk script sales.awk by clicking on the title below:
- sales.awk
# BEGIN BEGIN { FS="§" } # TABLE $1 !~ /^#/ && $1 !~ /^$/ { sales[$1]+=$2 } # END END { for (pc in sales) printf("PC Type : %s \t Sales (06+13+83) : %10d\n",pc,sales[pc]); }
This script contains 13 lines. The purpose of this script is to calculate the total number of computers sold in the three French departments from the data present in the sales file:
1 # BEGIN
2 BEGIN {
3 FS="§"
4 }
5 # TABLE
6 $1 !~ /^#/ && $1 !~ /^$/ {
7 sales[$1]+=$2
8 }
9 # END
10 END {
11 for (pc in sales)
12 printf("PC Type : %s \t Sales (06+13+83) : %10d\n",pc,sales[pc]);
13 }
It is important that you understand the key lines in the above script:
- Line 3,
- Defines a new field seperator in a BEGIN section.
- Line 6,
- Discards all commented and empty lines.
- Line 7,
- The table's key is $1, in other words the different types of computers. Against each key, the number of each type of computer sold is stored in $2. The += characters indicate that the value stored in $2 is incremental.
- Line 12,
- Uses printf to format the output of each line in the table.
Now execute the script and check the output is correct:
root@ubuntu1604:~# awk -f /home/trainee/Downloads/sales.awk /home/trainee/Downloads/sales.txt PC Type : Servers Sales (06+13+83) : 41 PC Type : Portables Sales (06+13+83) : 175 PC Type : Ipads Sales (06+13+83) : 76 PC Type : Desktops Sales (06+13+83) : 329
Other Useful Commands
The expand Command
The expand command converts tabulations in a file to spaces and prints the results to STDOUT. With no file as an argument or with the - character as an argument, the command takes it's input from STDIN.
Download the following file:
- expand.txt
un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq
Move the file to the /root folder:
root@ubuntu1604:~# mv /home/trainee/Downloads/expand.txt /root/expand
Use the cat command to view the contents of the file:
root@ubuntu1604:~# cat expand un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq un deux trois quatre cinq
Now use the -vet switches of the cat command to view the non-printable characters:
root@ubuntu1604:~# cat -vet expand un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$
[stextbox id='black' image='null'] Important : As you can see the tabulations are shown as ^I and the end o each line as a $. [/stextbox]
Now use the expand command to convert the tabulations into spaces and send the result to the expand1 file:
root@ubuntu1604:~# expand expand > expand1
View the resulting expand1 file with the cat command and the -vet switches:
root@ubuntu1604:~# cat -vet expand1 un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$
[stextbox id='black' image='null'] Important : As you can see, the tabulations have been changed into spaces. [/stextbox]
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the expand command to view the command line switches. [/stextbox]
La Commande unexpand
The expand command converts spaces in a file to tabulations and prints the results to STDOUT. With no file as an argument or with the - character as an argument, the command takes it's input from STDIN.
Now use the expand command to convert the spaces in the expand1 file into tabulations and send the result to the expand2 file:
root@ubuntu1604:~# cat -vet expand1 un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ un deux trois quatre cinq$ root@ubuntu1604:~# unexpand -a expand1 > expand2 root@ubuntu1604:~# cat -vet expand2 un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$ un^Ideux^Itrois^Iquatre^Icinq$
[stextbox id='black' image='null'] Important : Note that the spaces have been replaced by tabulations. [/stextbox]
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the unexpand command to view the command line switches. [/stextbox]
The cut command
The cut command splits each line of a file into columns starting with column 1. Each column contains one character. The command can also be used to split lines into fields where the default seperator is a tablulation. The default seperator can be changed by using the -d switch.
Select the first 7 columns of the /etc/passwd file:
root@ubuntu1604:~# cut -c1-7 /etc/passwd root:x: daemon: bin:x:2 sys:x:3 sync:x: games:x man:x:6 lp:x:7: mail:x: news:x: uucp:x: proxy:x www-dat backup: list:x: irc:x:3 gnats:x nobody: systemd systemd systemd systemd syslog: _apt:x: message uuidd:x lightdm whoopsi avahi-a avahi:x dnsmasq colord: speech- hplip:x kernoop pulse:x rtkit:x saned:x usbmux: trainee sshd:x:
In order to select columns 1 to 5, columns 10 to 15 and columns 30 and higher, us the following command:
root@ubuntu1604:~# cut -c1-5,10-15,30- /etc/passwd root:0:rootsh daemo1:1:da:/usr/sbin/nologin bin:x:bin:/nologin sys:x:sys:/nologin sync:65534:/sync games:60:ga:/usr/sbin/nologin man:x2:man::/usr/sbin/nologin lp:x:lp:/vasr/sbin/nologin mail:8:mailr/sbin/nologin news:9:newsws:/usr/sbin/nologin uucp::10:uuuucp:/usr/sbin/nologin proxy3:13:p/sbin/nologin www-dx:33:3r/www:/usr/sbin/nologin backu34:34:ckups:/usr/sbin/nologin list::38:Maager:/var/list:/usr/sbin/nologin irc:x39:ircd:/usr/sbin/nologin gnats1:41:Gting System (admin):/var/lib/gnats:/usr/sbin/nologin nobod65534:nonexistent:/usr/sbin/nologin systeimesynstemd Time Synchronization,,,:/run/systemd:/bin/false systeetworktemd Network Management,,,:/run/systemd/netif:/bin/false systeesolvetemd Resolver,,,:/run/systemd/resolve:/bin/false systeus-proystemd Bus Proxy,,,:/run/systemd:/bin/false syslo104:10g:/bin/false _apt:5:6553t:/bin/false messas:x:10n/dbus:/bin/false uuidd07:111bin/false light:108:1ay Manager:/var/lib/lightdm:/bin/false whoopx:109:ent:/bin/false avahioipd:x autoip daemon,,,:/var/lib/avahi-autoipd:/bin/false avahi11:120emon,,,:/var/run/avahi-daemon:/bin/false dnsma:112:6,:/var/lib/misc:/bin/false color113:12r management daemon,,,:/var/lib/colord:/bin/false speecspatcheech Dispatcher,,,:/var/run/speech-dispatcher:/bin/false hplip15:7:Her,,,:/var/run/hplip:/bin/false kernox:116:ops Tracking Daemon,,,:/:/bin/false pulse17:124emon,,,:/var/run/pulse:/bin/false rtkit18:126,:/proc:/bin/false saned19:127ed:/bin/false usbmu120:46,,,:/var/lib/usbmux:/bin/false train:1000:,:/home/trainee:/bin/bash sshd:1:6553hd:/usr/sbin/nologin
In order to select the 2nd, 4th and 6th column, use the following command:
root@ubuntu1604:~# cut -d: -f2,4,6 /etc/passwd x:0:/root x:1:/usr/sbin x:2:/bin x:3:/dev x:65534:/bin x:60:/usr/games x:12:/var/cache/man x:7:/var/spool/lpd x:8:/var/mail x:9:/var/spool/news x:10:/var/spool/uucp x:13:/bin x:33:/var/www x:34:/var/backups x:38:/var/list x:39:/var/run/ircd x:41:/var/lib/gnats x:65534:/nonexistent x:102:/run/systemd x:103:/run/systemd/netif x:104:/run/systemd/resolve x:105:/run/systemd x:108:/home/syslog x:65534:/nonexistent x:110:/var/run/dbus x:111:/run/uuidd x:114:/var/lib/lightdm x:116:/nonexistent x:119:/var/lib/avahi-autoipd x:120:/var/run/avahi-daemon x:65534:/var/lib/misc x:123:/var/lib/colord x:29:/var/run/speech-dispatcher x:7:/var/run/hplip x:65534:/ x:124:/var/run/pulse x:126:/proc x:127:/var/lib/saned x:46:/var/lib/usbmux x:1000:/home/trainee x:65534:/var/run/sshd
[stextbox id='black' image='null'] Important: Note the use of the -d switch to change the default seperator. [/stextbox]
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the cut command to view the command line switches. [/stextbox]
The uniq Command
The following command is used to extract the Primary Group GIDs from the /etc/passwd file:
root@ubuntu1604:~# cut -d: -f4 /etc/passwd | sort -n | uniq 0 1 2 3 7 8 9 10 12 13 29 33 34 38 39 41 46 60 102 103 104 105 108 110 111 114 116 119 120 123 124 126 127 1000 65534
[stextbox id='black' image='null'] Important: Note the use of the uniq command to remove duplicates from the list. [/stextbox]
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the uniq command to view the command line switches. [/stextbox]
The tr Command
The tr command is used to substitute certain characters by other characters. This command only accepts data from standard input (hence the pipe):
root@ubuntu1604:~# cat /etc/passwd | tr "[a-z]" "[A-Z]" ROOT:X:0:0:ROOT:/ROOT:/BIN/BASH DAEMON:X:1:1:DAEMON:/USR/SBIN:/USR/SBIN/NOLOGIN BIN:X:2:2:BIN:/BIN:/USR/SBIN/NOLOGIN SYS:X:3:3:SYS:/DEV:/USR/SBIN/NOLOGIN SYNC:X:4:65534:SYNC:/BIN:/BIN/SYNC GAMES:X:5:60:GAMES:/USR/GAMES:/USR/SBIN/NOLOGIN MAN:X:6:12:MAN:/VAR/CACHE/MAN:/USR/SBIN/NOLOGIN LP:X:7:7:LP:/VAR/SPOOL/LPD:/USR/SBIN/NOLOGIN MAIL:X:8:8:MAIL:/VAR/MAIL:/USR/SBIN/NOLOGIN NEWS:X:9:9:NEWS:/VAR/SPOOL/NEWS:/USR/SBIN/NOLOGIN UUCP:X:10:10:UUCP:/VAR/SPOOL/UUCP:/USR/SBIN/NOLOGIN PROXY:X:13:13:PROXY:/BIN:/USR/SBIN/NOLOGIN WWW-DATA:X:33:33:WWW-DATA:/VAR/WWW:/USR/SBIN/NOLOGIN BACKUP:X:34:34:BACKUP:/VAR/BACKUPS:/USR/SBIN/NOLOGIN LIST:X:38:38:MAILING LIST MANAGER:/VAR/LIST:/USR/SBIN/NOLOGIN IRC:X:39:39:IRCD:/VAR/RUN/IRCD:/USR/SBIN/NOLOGIN GNATS:X:41:41:GNATS BUG-REPORTING SYSTEM (ADMIN):/VAR/LIB/GNATS:/USR/SBIN/NOLOGIN NOBODY:X:65534:65534:NOBODY:/NONEXISTENT:/USR/SBIN/NOLOGIN SYSTEMD-TIMESYNC:X:100:102:SYSTEMD TIME SYNCHRONIZATION,,,:/RUN/SYSTEMD:/BIN/FALSE SYSTEMD-NETWORK:X:101:103:SYSTEMD NETWORK MANAGEMENT,,,:/RUN/SYSTEMD/NETIF:/BIN/FALSE SYSTEMD-RESOLVE:X:102:104:SYSTEMD RESOLVER,,,:/RUN/SYSTEMD/RESOLVE:/BIN/FALSE SYSTEMD-BUS-PROXY:X:103:105:SYSTEMD BUS PROXY,,,:/RUN/SYSTEMD:/BIN/FALSE SYSLOG:X:104:108::/HOME/SYSLOG:/BIN/FALSE _APT:X:105:65534::/NONEXISTENT:/BIN/FALSE MESSAGEBUS:X:106:110::/VAR/RUN/DBUS:/BIN/FALSE UUIDD:X:107:111::/RUN/UUIDD:/BIN/FALSE LIGHTDM:X:108:114:LIGHT DISPLAY MANAGER:/VAR/LIB/LIGHTDM:/BIN/FALSE WHOOPSIE:X:109:116::/NONEXISTENT:/BIN/FALSE AVAHI-AUTOIPD:X:110:119:AVAHI AUTOIP DAEMON,,,:/VAR/LIB/AVAHI-AUTOIPD:/BIN/FALSE AVAHI:X:111:120:AVAHI MDNS DAEMON,,,:/VAR/RUN/AVAHI-DAEMON:/BIN/FALSE DNSMASQ:X:112:65534:DNSMASQ,,,:/VAR/LIB/MISC:/BIN/FALSE COLORD:X:113:123:COLORD COLOUR MANAGEMENT DAEMON,,,:/VAR/LIB/COLORD:/BIN/FALSE SPEECH-DISPATCHER:X:114:29:SPEECH DISPATCHER,,,:/VAR/RUN/SPEECH-DISPATCHER:/BIN/FALSE HPLIP:X:115:7:HPLIP SYSTEM USER,,,:/VAR/RUN/HPLIP:/BIN/FALSE KERNOOPS:X:116:65534:KERNEL OOPS TRACKING DAEMON,,,:/:/BIN/FALSE PULSE:X:117:124:PULSEAUDIO DAEMON,,,:/VAR/RUN/PULSE:/BIN/FALSE RTKIT:X:118:126:REALTIMEKIT,,,:/PROC:/BIN/FALSE SANED:X:119:127::/VAR/LIB/SANED:/BIN/FALSE USBMUX:X:120:46:USBMUX DAEMON,,,:/VAR/LIB/USBMUX:/BIN/FALSE TRAINEE:X:1000:1000:TRAINEE,,,:/HOME/TRAINEE:/BIN/BASH SSHD:X:121:65534::/VAR/RUN/SSHD:/USR/SBIN/NOLOGIN
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the tr command to view the command line switches. [/stextbox]
The paste Command
The paste command concatenates lines from n files. For example:
root@ubuntu1604:~# paste -d: /etc/passwd /etc/shadow root:x:0:0:root:/root:/bin/bash:root:!:16924:0:99999:7::: daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin:daemon:*:16911:0:99999:7::: bin:x:2:2:bin:/bin:/usr/sbin/nologin:bin:*:16911:0:99999:7::: sys:x:3:3:sys:/dev:/usr/sbin/nologin:sys:*:16911:0:99999:7::: sync:x:4:65534:sync:/bin:/bin/sync:sync:*:16911:0:99999:7::: games:x:5:60:games:/usr/games:/usr/sbin/nologin:games:*:16911:0:99999:7::: man:x:6:12:man:/var/cache/man:/usr/sbin/nologin:man:*:16911:0:99999:7::: lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin:lp:*:16911:0:99999:7::: mail:x:8:8:mail:/var/mail:/usr/sbin/nologin:mail:*:16911:0:99999:7::: news:x:9:9:news:/var/spool/news:/usr/sbin/nologin:news:*:16911:0:99999:7::: uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin:uucp:*:16911:0:99999:7::: proxy:x:13:13:proxy:/bin:/usr/sbin/nologin:proxy:*:16911:0:99999:7::: www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin:www-data:*:16911:0:99999:7::: backup:x:34:34:backup:/var/backups:/usr/sbin/nologin:backup:*:16911:0:99999:7::: list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin:list:*:16911:0:99999:7::: irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin:irc:*:16911:0:99999:7::: gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin:gnats:*:16911:0:99999:7::: nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin:nobody:*:16911:0:99999:7::: systemd-timesync:x:100:102:systemd Time Synchronization,,,:/run/systemd:/bin/false:systemd-timesync:*:16911:0:99999:7::: systemd-network:x:101:103:systemd Network Management,,,:/run/systemd/netif:/bin/false:systemd-network:*:16911:0:99999:7::: systemd-resolve:x:102:104:systemd Resolver,,,:/run/systemd/resolve:/bin/false:systemd-resolve:*:16911:0:99999:7::: systemd-bus-proxy:x:103:105:systemd Bus Proxy,,,:/run/systemd:/bin/false:systemd-bus-proxy:*:16911:0:99999:7::: syslog:x:104:108::/home/syslog:/bin/false:syslog:*:16911:0:99999:7::: _apt:x:105:65534::/nonexistent:/bin/false:_apt:*:16911:0:99999:7::: messagebus:x:106:110::/var/run/dbus:/bin/false:messagebus:*:16911:0:99999:7::: uuidd:x:107:111::/run/uuidd:/bin/false:uuidd:*:16911:0:99999:7::: lightdm:x:108:114:Light Display Manager:/var/lib/lightdm:/bin/false:lightdm:*:16911:0:99999:7::: whoopsie:x:109:116::/nonexistent:/bin/false:whoopsie:*:16911:0:99999:7::: avahi-autoipd:x:110:119:Avahi autoip daemon,,,:/var/lib/avahi-autoipd:/bin/false:avahi-autoipd:*:16911:0:99999:7::: avahi:x:111:120:Avahi mDNS daemon,,,:/var/run/avahi-daemon:/bin/false:avahi:*:16911:0:99999:7::: dnsmasq:x:112:65534:dnsmasq,,,:/var/lib/misc:/bin/false:dnsmasq:*:16911:0:99999:7::: colord:x:113:123:colord colour management daemon,,,:/var/lib/colord:/bin/false:colord:*:16911:0:99999:7::: speech-dispatcher:x:114:29:Speech Dispatcher,,,:/var/run/speech-dispatcher:/bin/false:speech-dispatcher:!:16911:0:99999:7::: hplip:x:115:7:HPLIP system user,,,:/var/run/hplip:/bin/false:hplip:*:16911:0:99999:7::: kernoops:x:116:65534:Kernel Oops Tracking Daemon,,,:/:/bin/false:kernoops:*:16911:0:99999:7::: pulse:x:117:124:PulseAudio daemon,,,:/var/run/pulse:/bin/false:pulse:*:16911:0:99999:7::: rtkit:x:118:126:RealtimeKit,,,:/proc:/bin/false:rtkit:*:16911:0:99999:7::: saned:x:119:127::/var/lib/saned:/bin/false:saned:*:16911:0:99999:7::: usbmux:x:120:46:usbmux daemon,,,:/var/lib/usbmux:/bin/false:usbmux:*:16911:0:99999:7::: trainee:x:1000:1000:trainee,,,:/home/trainee:/bin/bash:trainee:$6$cloNcVp0$4BFXvmH./lvuhem.pWND1.XgChp/BuT4tHukwvFR9ykdQM1Yt.WbMO60lHdUR/E6D2bqUJ/n.BwX4gCMle/671:16924:0:99999:7::: sshd:x:121:65534::/var/run/sshd:/usr/sbin/nologin:sshd:*:16924:0:99999:7:::
[stextbox id='black' image='null'] Important: Note that you need to become root to be able to execute this command. The reason is that normal users do not have the right to read the /etc/shadow file. [/stextbox]
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the paste command to view the command line switches. [/stextbox]
The split Command
The split command is used to divide a large file into smaller segments. Create an empty 250 MB file as follows:
root@ubuntu1604:~# dd if=/dev/zero of=/file bs=1024k count=250 250+0 records in 250+0 records out 262144000 bytes (262 MB, 250 MiB) copied, 2,57217 s, 102 MB/s
Now use the split command to divide the file into 5 smaller files each of 50:
root@ubuntu1604:~# split -b 50m /file filepart root@ubuntu1604:~# ls -l | grep filepart -rw-r--r-- 1 root root 52428800 déc. 17 11:31 filepartaa -rw-r--r-- 1 root root 52428800 déc. 17 11:31 filepartab -rw-r--r-- 1 root root 52428800 déc. 17 11:31 filepartac -rw-r--r-- 1 root root 52428800 déc. 17 11:31 filepartad -rw-r--r-- 1 root root 52428800 déc. 17 11:31 filepartae
[stextbox id='black' image='null'] Important: Note that the 5 files were created in the current working directory. [/stextbox]
You can re-construct the original file by using the cat command:
root@ubuntu1604:~# cat fileparta* > newfile root@ubuntu1604:~# ls -l | grep newf -rw-r--r-- 1 root root 262144000 déc. 17 11:32 newfile
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the split command to view the command line switches. [/stextbox]
The diff Command
The diff command compares two fles and indicates what changes need to be made to the first file in order that it be identical to the second file.
Copy the /etc/passwd file to the /root directory:
root@ubuntu1604:~# cp /etc/passwd /root
Edit the */root/passwd file as shown:
... trainee10:x:1000:1000:trainee:/home/trainee:/bin/bash ...
Delete the lp entry and add the following line to the end of /root/passwd:
... Linux is great!
Now compare the two files:
root@ubuntu1604:~# diff /etc/passwd /root/passwd 8d7 < lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin 40c39 < trainee:x:1000:1000:trainee,,,:/home/trainee:/bin/bash --- > trainee10:x:1000:1000:trainee,,,:/home/trainee:/bin/bash 41a41 > Linux is great!
In this output you will notice the < and > characters. The first makes reference to the first file, /etc/passwd, whist the second makes reference to the second file, /root/passwd.
The output 8d7 means that line 8 needs to be deleted in /etc/passwd because it is missing in /root/passwd.
The output 40c39 means that at line 40 in /etc/passwd needs to be modified in order to be the same as line 39 in /root/passwd.
The output 41a41 means that at line 41 in /root/passwd line 41 in /etc/passwd needs to be added because it is missing.
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the diff command to view the command line switches. [/stextbox]
The cmp Command
The cmp command compares two files character by character. By default, the command stops after finding the first difference:
root@ubuntu1604:~# cmp /root/passwd /etc/passwd /root/passwd /etc/passwd differ: byte 286, line 8
The -l switch shows all of the differences in a three column format:
root@ubuntu1604:~# cmp -l /root/passwd /etc/passwd | more cmp: EOF on /root/passwd 286 155 154 287 141 160 288 151 72 289 154 170 291 170 67 293 70 67 295 70 154 296 72 160 297 155 72 298 141 57 299 151 166 300 154 141 301 72 162 303 166 163 304 141 160 305 162 157 306 57 157 307 155 154 308 141 57 309 151 154 310 154 160 311 72 144 312 57 72 --More--
The first column represents the character number, the second column represents the ASCII octal value of the character in the /root/passwd file and the third column represents the ASCII octal value of the character in the /etc/passwd file.
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the cmp command to view the command line switches. [/stextbox]
The patch Command
The patch command is used to apply modifications contained within a patch file to an older version of a file so that it becomes the newer version of the file.
If you recall, you made some changes to the original greptest file that you downloaded:
root@ubuntu1604:~# cat /tmp/greptest # Starting comment ^ This line will be used to demonstrate the use of fgrep fenestrOS fenestros # Another comment 555-5555 f .fenestros .fe £ # End comment
You also used egrep to remove all the comments and empty lines and save the result to /tmp/greptest1:
root@ubuntu1604:~# cat /tmp/greptest1 fenestrOS fenestros 555-5555 f .fenestros .fe £
Now create a patch file containing the modifications that need to be applied to /tmp/greptest in order for it to be identical to /tmp/greptest1:
root@ubuntu1604:~# cd /tmp root@ubuntu1604:/tmp# diff -u greptest greptest1 > greptest.patch
A look at the patch file shows the chnages that need to be made to the greptest file:
root@ubuntu1604:/tmp# cat /tmp/greptest.patch --- greptest 2016-12-09 15:47:38.836983792 +0100 +++ greptest1 2016-12-09 15:46:15.976860968 +0100 @@ -1,14 +1,7 @@ -# Starting comment -^ This line will be used to demonstrate the use of fgrep fenestrOS fenestros -# Another comment 555-5555 f - .fenestros - .fe - £ -# End comment
Now apply the patch file:
root@ubuntu1604:/tmp# patch < greptest.patch patching file greptest
Finally, check the contents of the patched greptest file:
root@ubuntu1604:/tmp# cat greptest fenestrOS fenestros 555-5555 f .fenestros .fe £
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the patch command to view the command line switches. [/stextbox]
The strings Command
The strings Command is used to extract any printable string in one or more object files or executables. An object fie is an intermediary file used when compiling.
The format of an object file is ELF (Executable and Linkable Format). This same format is also used for:
- executables,
- shared libraries,
- core dumps.
Used as is, the command extracts all strings greater than 4 characters in length:
root@ubuntu1604:/tmp# strings /usr/bin/passwd | more /lib64/ld-linux-x86-64.so.2 kgUa libpam.so.0 _ITM_deregisterTMCloneTable __gmon_start__ _Jv_RegisterClasses _ITM_registerTMCloneTable pam_start pam_strerror pam_chauthtok pam_end libpam_misc.so.0 misc_conv libselinux.so.1 _init is_selinux_enabled security_getenforce context_user_get security_compute_av matchpathcon freecon context_free setfscreatecon --More--
Print the offset within the file before each string:
root@ubuntu1604:/tmp# strings -t d /usr/bin/passwd | more
568 /lib64/ld-linux-x86-64.so.2
823 kgUa
4241 libpam.so.0
4253 _ITM_deregisterTMCloneTable
4281 __gmon_start__
4296 _Jv_RegisterClasses
4316 _ITM_registerTMCloneTable
4342 pam_start
4352 pam_strerror
4365 pam_chauthtok
4379 pam_end
4387 libpam_misc.so.0
4404 misc_conv
4414 libselinux.so.1
4430 _init
4436 is_selinux_enabled
4455 security_getenforce
4475 context_user_get
4492 security_compute_av
4512 matchpathcon
4525 freecon
4533 context_free
4546 setfscreatecon
--More--
The -t switch can take one of three arguments that specify the numbering system to use:
| Argument | Numbering System |
|---|---|
| d | Decimal |
| o | Octal |
| x | Hexadecimal |
The -n switch prints sequences of characters that are at least min-len characters long, instead of the default 4:
root@ubuntu1604:/tmp# strings -t d -n 15 /usr/bin/passwd | more
568 /lib64/ld-linux-x86-64.so.2
4253 _ITM_deregisterTMCloneTable
4296 _Jv_RegisterClasses
4316 _ITM_registerTMCloneTable
4387 libpam_misc.so.0
4414 libselinux.so.1
4436 is_selinux_enabled
4455 security_getenforce
4475 context_user_get
4492 security_compute_av
4774 __stack_chk_fail
4942 __errno_location
5405 __libc_start_main
5537 LIBPAM_MISC_1.0
34456 Usage: %s [options] [LOGIN]
34496 -a, --all report password status on all accounts
34568 -d, --delete delete the password for the named accoun
t
34648 -e, --expire force expire the password for the named
account
34736 -h, --help display this help message and exit
34808 -k, --keep-tokens change password only if expired
34880 -i, --inactive INACTIVE set password inactive after expiration
--More--
The -f switch prints the name of the file before each string:
root@ubuntu1604:/tmp# strings -f /bin/* | grep "(c)" /bin/ntfscat: Copyright (c) 2003-2005 Richard Russon /bin/ntfscat: Copyright (c) 2003-2005 Anton Altaparmakov /bin/ntfscat: Copyright (c) 2003-2005 Szabolcs Szakacsits /bin/ntfscat: Copyright (c) 2007 Yura Pakhuchiy /bin/ntfscluster: Copyright (c) 2002-2003 Richard Russon /bin/ntfscluster: Copyright (c) 2005 Anton Altaparmakov /bin/ntfscluster: Copyright (c) 2005-2006 Szabolcs Szakacsits /bin/ntfsfallocate: Copyright (c) 2013-2014 Jean-Pierre Andre /bin/ntfsfix: Copyright (c) 2000-2006 Anton Altaparmakov /bin/ntfsfix: Copyright (c) 2002-2006 Szabolcs Szakacsits /bin/ntfsfix: Copyright (c) 2007 Yura Pakhuchiy /bin/ntfsfix: Copyright (c) 2011-2015 Jean-Pierre Andre /bin/ntfsinfo: Copyright (c) /bin/ntfsls: Copyright (c) 2003-2005 Anton Altaparmakov /bin/ntfsls: Copyright (c) 2003 Richard Russon /bin/ntfsls: Copyright (c) 2004 Carmelo Kintana /bin/ntfsls: Copyright (c) 2004 Giang Nguyen /bin/ntfsls: Copyright (c) 2003 Lode Leroy /bin/ntfsmove: Copyright (c) 2003 Richard Russon /bin/ntfstruncate: Copyright (c) 2002-2005 Anton Altaparmakov /bin/ntfstruncate: Copyright (c) 2003 Richard Russon /bin/ntfswipe: Copyright (c) 2002-2005 Richard Russon /bin/ntfswipe: Copyright (c) 2004 Yura Pakhuchiy /bin/ping: @(#) Copyright (c) 1989 The Regents of the University of California. /bin/ping6: @(#) Copyright (c) 1989 The Regents of the University of California..
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the strings command to view the command line switches. [/stextbox]
The comm Command
This command compares two text files and prints the differences to standard output:
root@ubuntu1604:/tmp# comm /etc/passwd /root/passwd root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/nologin sync:x:4:65534:sync:/bin:/bin/sync games:x:5:60:games:/usr/games:/usr/sbin/nologin man:x:6:12:man:/var/cache/man:/usr/sbin/nologin lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin mail:x:8:8:mail:/var/mail:/usr/sbin/nologin news:x:9:9:news:/var/spool/news:/usr/sbin/nologin uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin comm: file 1 is not in sorted order comm: file 2 is not in sorted order proxy:x:13:13:proxy:/bin:/usr/sbin/nologin www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin backup:x:34:34:backup:/var/backups:/usr/sbin/nologin list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin systemd-timesync:x:100:102:systemd Time Synchronization,,,:/run/systemd:/bin/false systemd-network:x:101:103:systemd Network Management,,,:/run/systemd/netif:/bin/false systemd-resolve:x:102:104:systemd Resolver,,,:/run/systemd/resolve:/bin/false systemd-bus-proxy:x:103:105:systemd Bus Proxy,,,:/run/systemd:/bin/false syslog:x:104:108::/home/syslog:/bin/false _apt:x:105:65534::/nonexistent:/bin/false messagebus:x:106:110::/var/run/dbus:/bin/false uuidd:x:107:111::/run/uuidd:/bin/false lightdm:x:108:114:Light Display Manager:/var/lib/lightdm:/bin/false whoopsie:x:109:116::/nonexistent:/bin/false avahi-autoipd:x:110:119:Avahi autoip daemon,,,:/var/lib/avahi-autoipd:/bin/false avahi:x:111:120:Avahi mDNS daemon,,,:/var/run/avahi-daemon:/bin/false dnsmasq:x:112:65534:dnsmasq,,,:/var/lib/misc:/bin/false colord:x:113:123:colord colour management daemon,,,:/var/lib/colord:/bin/false speech-dispatcher:x:114:29:Speech Dispatcher,,,:/var/run/speech-dispatcher:/bin/false hplip:x:115:7:HPLIP system user,,,:/var/run/hplip:/bin/false kernoops:x:116:65534:Kernel Oops Tracking Daemon,,,:/:/bin/false pulse:x:117:124:PulseAudio daemon,,,:/var/run/pulse:/bin/false rtkit:x:118:126:RealtimeKit,,,:/proc:/bin/false saned:x:119:127::/var/lib/saned:/bin/false usbmux:x:120:46:usbmux daemon,,,:/var/lib/usbmux:/bin/false trainee10:x:1000:1000:trainee,,,:/home/trainee:/bin/bash sshd:x:121:65534::/var/run/sshd:/usr/sbin/nologin Linux is great! trainee:x:1000:1000:trainee,,,:/home/trainee:/bin/bash sshd:x:121:65534::/var/run/sshd:/usr/sbin/nologin
[stextbox id='black' image='null'] Important: The lines to the left are those that only appear in the first file. The lines on the right are those that exist in both files. The lines in the middle are those that only exist in the second file. [/stextbox]
If you only want to see the lines common to both files, use the following command:
root@ubuntu1604:/tmp# comm -12 /etc/passwd /root/passwd root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/nologin sync:x:4:65534:sync:/bin:/bin/sync games:x:5:60:games:/usr/games:/usr/sbin/nologin man:x:6:12:man:/var/cache/man:/usr/sbin/nologin mail:x:8:8:mail:/var/mail:/usr/sbin/nologin news:x:9:9:news:/var/spool/news:/usr/sbin/nologin uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin comm: file 1 is not in sorted order comm: file 2 is not in sorted order proxy:x:13:13:proxy:/bin:/usr/sbin/nologin www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin backup:x:34:34:backup:/var/backups:/usr/sbin/nologin list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin systemd-timesync:x:100:102:systemd Time Synchronization,,,:/run/systemd:/bin/false systemd-network:x:101:103:systemd Network Management,,,:/run/systemd/netif:/bin/false systemd-resolve:x:102:104:systemd Resolver,,,:/run/systemd/resolve:/bin/false systemd-bus-proxy:x:103:105:systemd Bus Proxy,,,:/run/systemd:/bin/false syslog:x:104:108::/home/syslog:/bin/false _apt:x:105:65534::/nonexistent:/bin/false messagebus:x:106:110::/var/run/dbus:/bin/false uuidd:x:107:111::/run/uuidd:/bin/false lightdm:x:108:114:Light Display Manager:/var/lib/lightdm:/bin/false whoopsie:x:109:116::/nonexistent:/bin/false avahi-autoipd:x:110:119:Avahi autoip daemon,,,:/var/lib/avahi-autoipd:/bin/false avahi:x:111:120:Avahi mDNS daemon,,,:/var/run/avahi-daemon:/bin/false dnsmasq:x:112:65534:dnsmasq,,,:/var/lib/misc:/bin/false colord:x:113:123:colord colour management daemon,,,:/var/lib/colord:/bin/false speech-dispatcher:x:114:29:Speech Dispatcher,,,:/var/run/speech-dispatcher:/bin/false hplip:x:115:7:HPLIP system user,,,:/var/run/hplip:/bin/false kernoops:x:116:65534:Kernel Oops Tracking Daemon,,,:/:/bin/false pulse:x:117:124:PulseAudio daemon,,,:/var/run/pulse:/bin/false rtkit:x:118:126:RealtimeKit,,,:/proc:/bin/false saned:x:119:127::/var/lib/saned:/bin/false usbmux:x:120:46:usbmux daemon,,,:/var/lib/usbmux:/bin/false
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the comm command to view the command line switches. [/stextbox]
The head Command
The head command is used to display the first x lines of a file. The default value of x is 10:
root@ubuntu1604:/tmp# head /etc/passwd root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/nologin sync:x:4:65534:sync:/bin:/bin/sync games:x:5:60:games:/usr/games:/usr/sbin/nologin man:x:6:12:man:/var/cache/man:/usr/sbin/nologin lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin mail:x:8:8:mail:/var/mail:/usr/sbin/nologin news:x:9:9:news:/var/spool/news:/usr/sbin/nologin
You can change the default value of x by using the -n switch:
root@ubuntu1604:/tmp# head -n 15 /etc/passwd root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/nologin sync:x:4:65534:sync:/bin:/bin/sync games:x:5:60:games:/usr/games:/usr/sbin/nologin man:x:6:12:man:/var/cache/man:/usr/sbin/nologin lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin mail:x:8:8:mail:/var/mail:/usr/sbin/nologin news:x:9:9:news:/var/spool/news:/usr/sbin/nologin uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin proxy:x:13:13:proxy:/bin:/usr/sbin/nologin www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin backup:x:34:34:backup:/var/backups:/usr/sbin/nologin list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin
The command can also be used to display the first y bytes of a file by using the -c switch:
root@ubuntu1604:/tmp# head -c 150 /etc/passwd root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/noloroot@ubuntu1604:/tmp#
If the value of y is negative, head displays all bytes in the file except the last y bytes:
root@ubuntu1604:/tmp# head -c 150 /etc/passwd root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/noloroot@ubuntu1604:/tmp# root@ubuntu1604:/tmp# head -c -150 /etc/passwd root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/nologin sync:x:4:65534:sync:/bin:/bin/sync games:x:5:60:games:/usr/games:/usr/sbin/nologin man:x:6:12:man:/var/cache/man:/usr/sbin/nologin lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin mail:x:8:8:mail:/var/mail:/usr/sbin/nologin news:x:9:9:news:/var/spool/news:/usr/sbin/nologin uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin proxy:x:13:13:proxy:/bin:/usr/sbin/nologin www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin backup:x:34:34:backup:/var/backups:/usr/sbin/nologin list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin systemd-timesync:x:100:102:systemd Time Synchronization,,,:/run/systemd:/bin/false systemd-network:x:101:103:systemd Network Management,,,:/run/systemd/netif:/bin/false systemd-resolve:x:102:104:systemd Resolver,,,:/run/systemd/resolve:/bin/false systemd-bus-proxy:x:103:105:systemd Bus Proxy,,,:/run/systemd:/bin/false syslog:x:104:108::/home/syslog:/bin/false _apt:x:105:65534::/nonexistent:/bin/false messagebus:x:106:110::/var/run/dbus:/bin/false uuidd:x:107:111::/run/uuidd:/bin/false lightdm:x:108:114:Light Display Manager:/var/lib/lightdm:/bin/false whoopsie:x:109:116::/nonexistent:/bin/false avahi-autoipd:x:110:119:Avahi autoip daemon,,,:/var/lib/avahi-autoipd:/bin/false avahi:x:111:120:Avahi mDNS daemon,,,:/var/run/avahi-daemon:/bin/false dnsmasq:x:112:65534:dnsmasq,,,:/var/lib/misc:/bin/false colord:x:113:123:colord colour management daemon,,,:/var/lib/colord:/bin/false speech-dispatcher:x:114:29:Speech Dispatcher,,,:/var/run/speech-dispatcher:/bin/false hplip:x:115:7:HPLIP system user,,,:/var/run/hplip:/bin/false kernoops:x:116:65534:Kernel Oops Tracking Daemon,,,:/:/bin/false pulse:x:117:124:PulseAudio daemon,,,:/var/run/pulse:/bin/false rtkit:x:118:126:RealtimeKit,,,:/proc:/bin/false saned:x:119:127::/var/lib/saned:/bin/false usbmux:x:120:46root@ubuntu1604:/tmp#
Both x and y can accept multipliers:
root@ubuntu1604:/tmp# head -c 1b /etc/passwd root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/nologin sync:x:4:65534:sync:/bin:/bin/sync games:x:5:60:games:/usr/games:/usr/sbin/nologin man:x:6:12:man:/var/cache/man:/usr/sbin/nologin lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin mail:x:8:8:mail:/var/mail:/usr/sbin/nologin news:x:9:9:news:/var/spool/news:/usr/sbin/nologin uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin proxy:x:13:13:proxy:/bin:/usr/sbin/nroot@ubuntu1604:/tmp# root@ubuntu1604:/tmp# root@ubuntu1604:/tmp# head -c 512 /etc/passwd root:x:0:0:root:/root:/bin/bash daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin bin:x:2:2:bin:/bin:/usr/sbin/nologin sys:x:3:3:sys:/dev:/usr/sbin/nologin sync:x:4:65534:sync:/bin:/bin/sync games:x:5:60:games:/usr/games:/usr/sbin/nologin man:x:6:12:man:/var/cache/man:/usr/sbin/nologin lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin mail:x:8:8:mail:/var/mail:/usr/sbin/nologin news:x:9:9:news:/var/spool/news:/usr/sbin/nologin uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin proxy:x:13:13:proxy:/bin:/usr/sbin/nroot@ubuntu1604:/tmp
The common multipliers are:
| Multiplier | Number of bytes |
|---|---|
| b | 512 |
| KB | 1000 |
| K | 1024 |
| MB | 1000*1000 |
| M | 1024*1024 |
| GB | 1000*1000*1000 |
| G | 1024*1024*1024 |
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the head command to view the command line switches. [/stextbox]
The tail Command
The tail command is used to display the last x lines of a file. The default value of x is 10:
root@ubuntu1604:/tmp# tail /etc/passwd colord:x:113:123:colord colour management daemon,,,:/var/lib/colord:/bin/false speech-dispatcher:x:114:29:Speech Dispatcher,,,:/var/run/speech-dispatcher:/bin/false hplip:x:115:7:HPLIP system user,,,:/var/run/hplip:/bin/false kernoops:x:116:65534:Kernel Oops Tracking Daemon,,,:/:/bin/false pulse:x:117:124:PulseAudio daemon,,,:/var/run/pulse:/bin/false rtkit:x:118:126:RealtimeKit,,,:/proc:/bin/false saned:x:119:127::/var/lib/saned:/bin/false usbmux:x:120:46:usbmux daemon,,,:/var/lib/usbmux:/bin/false trainee:x:1000:1000:trainee,,,:/home/trainee:/bin/bash sshd:x:121:65534::/var/run/sshd:/usr/sbin/nolog
You can change the default value of x by using the -n switch:
root@ubuntu1604:/tmp# tail -n 15 /etc/passwd lightdm:x:108:114:Light Display Manager:/var/lib/lightdm:/bin/false whoopsie:x:109:116::/nonexistent:/bin/false avahi-autoipd:x:110:119:Avahi autoip daemon,,,:/var/lib/avahi-autoipd:/bin/false avahi:x:111:120:Avahi mDNS daemon,,,:/var/run/avahi-daemon:/bin/false dnsmasq:x:112:65534:dnsmasq,,,:/var/lib/misc:/bin/false colord:x:113:123:colord colour management daemon,,,:/var/lib/colord:/bin/false speech-dispatcher:x:114:29:Speech Dispatcher,,,:/var/run/speech-dispatcher:/bin/false hplip:x:115:7:HPLIP system user,,,:/var/run/hplip:/bin/false kernoops:x:116:65534:Kernel Oops Tracking Daemon,,,:/:/bin/false pulse:x:117:124:PulseAudio daemon,,,:/var/run/pulse:/bin/false rtkit:x:118:126:RealtimeKit,,,:/proc:/bin/false saned:x:119:127::/var/lib/saned:/bin/false usbmux:x:120:46:usbmux daemon,,,:/var/lib/usbmux:/bin/false trainee:x:1000:1000:trainee,,,:/home/trainee:/bin/bash sshd:x:121:65534::/var/run/sshd:/usr/sbin/nologin
The command can also be used to display the last y bytes of a file by using the -c switch:
root@ubuntu1604:/tmp# tail -c 150 /etc/passwd :usbmux daemon,,,:/var/lib/usbmux:/bin/false trainee:x:1000:1000:trainee,,,:/home/trainee:/bin/bash sshd:x:121:65534::/var/run/sshd:/usr/sbin/nologin
If the value of y is positive, tail displays all bytes in the file after the yth byte:
root@ubuntu1604:/tmp# tail -c +150 /etc/passwd ogin sync:x:4:65534:sync:/bin:/bin/sync games:x:5:60:games:/usr/games:/usr/sbin/nologin man:x:6:12:man:/var/cache/man:/usr/sbin/nologin lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin mail:x:8:8:mail:/var/mail:/usr/sbin/nologin news:x:9:9:news:/var/spool/news:/usr/sbin/nologin uucp:x:10:10:uucp:/var/spool/uucp:/usr/sbin/nologin proxy:x:13:13:proxy:/bin:/usr/sbin/nologin www-data:x:33:33:www-data:/var/www:/usr/sbin/nologin backup:x:34:34:backup:/var/backups:/usr/sbin/nologin list:x:38:38:Mailing List Manager:/var/list:/usr/sbin/nologin irc:x:39:39:ircd:/var/run/ircd:/usr/sbin/nologin gnats:x:41:41:Gnats Bug-Reporting System (admin):/var/lib/gnats:/usr/sbin/nologin nobody:x:65534:65534:nobody:/nonexistent:/usr/sbin/nologin systemd-timesync:x:100:102:systemd Time Synchronization,,,:/run/systemd:/bin/false systemd-network:x:101:103:systemd Network Management,,,:/run/systemd/netif:/bin/false systemd-resolve:x:102:104:systemd Resolver,,,:/run/systemd/resolve:/bin/false systemd-bus-proxy:x:103:105:systemd Bus Proxy,,,:/run/systemd:/bin/false syslog:x:104:108::/home/syslog:/bin/false _apt:x:105:65534::/nonexistent:/bin/false messagebus:x:106:110::/var/run/dbus:/bin/false uuidd:x:107:111::/run/uuidd:/bin/false lightdm:x:108:114:Light Display Manager:/var/lib/lightdm:/bin/false whoopsie:x:109:116::/nonexistent:/bin/false avahi-autoipd:x:110:119:Avahi autoip daemon,,,:/var/lib/avahi-autoipd:/bin/false avahi:x:111:120:Avahi mDNS daemon,,,:/var/run/avahi-daemon:/bin/false dnsmasq:x:112:65534:dnsmasq,,,:/var/lib/misc:/bin/false colord:x:113:123:colord colour management daemon,,,:/var/lib/colord:/bin/false speech-dispatcher:x:114:29:Speech Dispatcher,,,:/var/run/speech-dispatcher:/bin/false hplip:x:115:7:HPLIP system user,,,:/var/run/hplip:/bin/false kernoops:x:116:65534:Kernel Oops Tracking Daemon,,,:/:/bin/false pulse:x:117:124:PulseAudio daemon,,,:/var/run/pulse:/bin/false rtkit:x:118:126:RealtimeKit,,,:/proc:/bin/false saned:x:119:127::/var/lib/saned:/bin/false usbmux:x:120:46:usbmux daemon,,,:/var/lib/usbmux:/bin/false trainee:x:1000:1000:trainee,,,:/home/trainee:/bin/bash sshd:x:121:65534::/var/run/sshd:/usr/sbin/nologin
Both x and y can accept multipliers:
root@ubuntu1604:/tmp# tail -c 1b /etc/passwd :114:29:Speech Dispatcher,,,:/var/run/speech-dispatcher:/bin/false hplip:x:115:7:HPLIP system user,,,:/var/run/hplip:/bin/false kernoops:x:116:65534:Kernel Oops Tracking Daemon,,,:/:/bin/false pulse:x:117:124:PulseAudio daemon,,,:/var/run/pulse:/bin/false rtkit:x:118:126:RealtimeKit,,,:/proc:/bin/false saned:x:119:127::/var/lib/saned:/bin/false usbmux:x:120:46:usbmux daemon,,,:/var/lib/usbmux:/bin/false trainee:x:1000:1000:trainee,,,:/home/trainee:/bin/bash sshd:x:121:65534::/var/run/sshd:/usr/sbin/nologin root@ubuntu1604:/tmp# root@ubuntu1604:/tmp# tail -c 512 /etc/passwd :114:29:Speech Dispatcher,,,:/var/run/speech-dispatcher:/bin/false hplip:x:115:7:HPLIP system user,,,:/var/run/hplip:/bin/false kernoops:x:116:65534:Kernel Oops Tracking Daemon,,,:/:/bin/false pulse:x:117:124:PulseAudio daemon,,,:/var/run/pulse:/bin/false rtkit:x:118:126:RealtimeKit,,,:/proc:/bin/false saned:x:119:127::/var/lib/saned:/bin/false usbmux:x:120:46:usbmux daemon,,,:/var/lib/usbmux:/bin/false trainee:x:1000:1000:trainee,,,:/home/trainee:/bin/bash sshd:x:121:65534::/var/run/sshd:/usr/sbin/nologin
The common multipliers are:
| Multiplier | Number of bytes |
|---|---|
| b | 512 |
| KB | 1000 |
| K | 1024 |
| MB | 1000*1000 |
| M | 1024*1024 |
| GB | 1000*1000*1000 |
| G | 1024*1024*1024 |
A useful switch to use with the tail command is -f. This switch continually updates the output:
root@ubuntu1604:/tmp# tail -f /var/log/syslog Dec 17 13:22:35 ubuntu1604 sh[870]: Sleeping '888' '888' Dec 17 14:16:59 ubuntu1604 sh[870]: message repeated 465 times: [ Sleeping '888' '888'] Dec 17 14:17:01 ubuntu1604 CRON[17224]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly) Dec 17 14:17:06 ubuntu1604 sh[870]: Sleeping '888' '888' Dec 17 15:17:00 ubuntu1604 sh[870]: message repeated 512 times: [ Sleeping '888' '888'] Dec 17 15:17:01 ubuntu1604 CRON[30516]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly) Dec 17 15:17:07 ubuntu1604 sh[870]: Sleeping '888' '888' Dec 17 15:30:00 ubuntu1604 sh[870]: message repeated 110 times: [ Sleeping '888' '888'] Dec 17 15:30:00 ubuntu1604 systemd[1]: snapd.refresh.timer: Adding 4h 29min 43.172868s random time. Dec 17 15:30:07 ubuntu1604 sh[870]: Sleeping '888' '888' ^C
Command Line Switches
[stextbox id='black' image='null'] To do : Use the –help option of the head command to view the command line switches. [/stextbox]
LAB #4 - Use the grep, tr and cut to extract your IP address from the output of ifconfig
root@ubuntu1604:/tmp# ifconfig enp0s3
enp0s3 Link encap:Ethernet HWaddr 08:00:27:20:4b:97
inet addr:10.0.2.15 Bcast:10.0.2.255 Mask:255.255.255.0
inet6 addr: fe80::c4db:2b29:aedd:e7ed/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:230127 errors:0 dropped:0 overruns:0 frame:0
TX packets:149877 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:238004530 (238.0 MB) TX bytes:10864892 (10.8 MB)
root@ubuntu1604:/tmp# ifconfig enp0s3 | grep "inet"
inet addr:10.0.2.15 Bcast:10.0.2.255 Mask:255.255.255.0
inet6 addr: fe80::c4db:2b29:aedd:e7ed/64 Scope:Link
root@ubuntu1604:/tmp# ifconfig enp0s3 | grep "inet" | grep -v "inet6"
inet addr:10.0.2.15 Bcast:10.0.2.255 Mask:255.255.255.0
root@ubuntu1604:/tmp# ifconfig enp0s3 | grep "inet" | grep -v "inet6" | tr -s " " ":"
:inet:addr:10.0.2.15:Bcast:10.0.2.255:Mask:255.255.255.0
root@ubuntu1604:/tmp# ifconfig enp0s3 | grep "inet" | grep -v "inet6" | tr -s " " ":" | cut -d: -f4
10.0.2.15
[stextbox id='black' image='null'] Important : Note the use of the -s switch with the tr command. This switch replaces a string of x identical characters with a single character. [/stextbox]
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