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filtercommands.md

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Filter Commands

Overview

Filter commands are used to filter the output so that the required things can easily be picked up. The commands which are used to filter the output are
$ less
$ more
$ head
$ tail
$ sort
$ cut
$ sed

less:-

  • The less command is used to see the output line wise or page wise.
    Ex: $ less /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

Note: -press Enter key to scroll down line by line (or)
Use d to go to next page
Use b to go to previous page
Use / to search for a word in the file Use v to go vi mode where you can edit the file and once you save it you will back to less command

more:-

  • More is exactly same like less
    Ex: $ more /etc/passwd

    Note: -press Enter key to scroll down line by line (or)
    Use d to go to next page
    Use / to search for a word in the file Use v to go vi mode where you can edit the file and once you save it you will back to more command

head:-

  • It is used to display the top 10 lines of the file.
    Ex: $ 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
  • To display the custom lines #head -n /etc/passwd (where n can be any number).
    Ex: $ head -3 /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

tail:-

  • It is used to display the last 10 lines of the file
    Ex: $ tail /etc/passwd
    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  
    lxd:x:106:65534::/var/lib/lxd/:/bin/false  
    messagebus:x:107:111::/var/run/dbus:/bin/false  
    uuidd:x:108:112::/run/uuidd:/bin/false  
    dnsmasq:x:109:65534:dnsmasq,,,:/var/lib/misc:/bin/false  
    sshd:x:110:65534::/var/run/sshd:/usr/sbin/nologin  
    pollinate:x:111:1::/var/cache/pollinate:/bin/false  
    krishnaprasadkv:x:1000:1000:,,,:/home/krishnaprasadkv:/bin/bash
  • To display the custom lines
    Ex: $ tail -3 /etc/passwd
    sshd:x:110:65534::/var/run/sshd:/usr/sbin/nologin  
    pollinate:x:111:1::/var/cache/pollinate:/bin/false  
    krishnaprasadkv:x:1000:1000:,,,:/home/krishnaprasadkv:/bin/bash

Sort:-

  • It is used to sort the output in numeric or alphabetic order. Syntax is sort filename

  • sort by alphabetic order

    • For testing purpose will use below file.

$ cat sample.txt

    welcome to CLI
    Linux basic commands
    Hello world
    testing
    scripts
    Hello world

$ sort sample.txt

    Hello world
    Hello world
    Linux basic commands
    scripts
    testing
    welcome to CLI
  • To sort the file according to numbers Ex: $ sort –d sample.txt
    1. Linux basic commands
    2. scripts
    3. Hello world
    4. welcome to CLI
    5. Hello world
    6. testing
  • To remove the duplicate entries from the output.
    Ex: $ sort –u sample.txt
    Hello world
    Linux basic commands
    scripts
    testing
    welcome to CLI

cut:-

  • The cut command is used to pick the given expression (in columns) and display the output.
    $ cut -d -f filename (where d stands for delimiter ex. : , “ “ etc and f stands for field)
  • To delimit colon(:) and print the field Ex: $ cut -d: -f1 /etc/passwd
    root
    daemon
    bin
    sys
    sync
    games
    man
    lp
    mail

To delimit spaces and print the field
Ex: $ cut –d “ “ –f1 sample.txt

    welcome
    Linux
    Hello
    testing
    scripts
    Hello

sed:-

  • sed stands for stream editor, which is used to search a word in the file and replace it with the word required to be in the output

$ sed ‘s/searchfor/replacewith/g’ filename
Note: it will only modify the output, but there will be no change in the original file.

Ex: $ sed 's/Hello/hai/g' sample.txt

    welcome to CLI
    Linux basic commands
    hai world
    testing
    scripts
    hai world
  • List help page of filter command with their option.

$ less --help $ more --help $ head --help
$ tail --help
$ sort --help
$ cut --help
$ sed --help