Bash One-liners: Linux, If, Else, For loop, Sed, Awk

Examples of useful bash one-liners


Bash One-linersUseful bash One-liners can improve your efficiency and make your work more enjoyable. Below is a collection of helpful bash one-liners.

Overview

Run a command against multiple targets in a single line

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for var in file1 file2;do cat $var;done

Find a directory that contains keyword

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find ./ -name *keyword*

Find all files modified in the last week

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find ./ -mtime -7

Find your external IP with curl

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curl l2.io/ip

Find your external IP with dig

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dig +short myip.opendns.com @resolver1.opendns.com

Tcpdump with timestamp in file name

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date +'%Y-%m-%d_%H_%M-%Z' | xargs -I {} bash -c "sudo tcpdump -nq -s 0 -i eth0 -w ./tcpdump-{}.pcap"

Delete dynamic and static arp for /24 subnet

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for i in {1..254}; do arp -d 10.0.0.$i; done

Custom watch function (ctrl+z SIGINT to stop)

Add function to current session or to ~/.bashrc:

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watch () { interrupted=false; trap "interrupted=true" INT; while ! $interrupted; do $*; sleep 1 || interrupted=true; done;}

Use function:

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watch grep alert /var/log/syslog

Tail file until keyword

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tail -f ./file.log | sed '/^Alert Found$/q'

Log SSH session

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ssh -l user host | tee -a ./file.txt

Function to print columns (shortcut to … | awk ‘{print $4, $9}’)

Add function to current session or to ~/.bashrc:

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col() { awk '{print $'$(echo $* | sed -e 's/ /,$/g')'}'; }

Use function:

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ls -l | col 4 9

List open files (-n skips dns resolution)

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lsof -n

Do not save command history of current session

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HISTFILE=

Copy files with progress indicator

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rsync --progress largefile.tar.gz other/location/

Check if file exists

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if [ -f file.exists.txt ] ; then echo "yes" ; else echo "no" ; fi

Add remote host public key to known hosts

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ssh-keyscan remote_server >>~/.ssh/known_hosts