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Bash Scripting

Iterate over a file

This script will iterate over a file and echo out every single line:

#!/bin/bash​for line in $(cat file.txt);do    echo $linedone

Another way of writing is this:

#!/bin/bash​while read p; do    echo  $pdone 


#!/bin/bash​for ((i = 0; i < 10; i++)); do    echo $idone

Another way to write this is by using the program seq. Seq is pretty much like range() in python. So it can be used like this:

#!/bin/bash​for x in `seq 1 100`; do    echo $xdone

If statement

$1 here represent the first argument.

​if [ "$1" == "" ]; then    echo "This happens"fi


#!/bin/bash​if [ "$1" == "" ]; then    echo "This happens"else    echo "Something else happens"fi

Command line arguments

Command line arguments are represented like this

This is the first command line argument.

Daemonize an execution

If you do a ping-sweep with host the command will take about a second to complete. And if you run that against 255 hosts I will take a long time to complete. To avoid this we can just deamonize every execution to make it faster. We use the & to daemonize it.

#!/bin/bash​for ip in $(cat ips.txt); do    ping -c 1 $ip &done

Use the output of command

It has happened to me several times that I want to input the output of a command into a new command, for example:

I search for a file, find three, and take the last line, which is a path. Now I want to cat that path:

#!/bin/bash​locate 646.c | tail -n 1

This can be done like this:

#!/bin/bash​cat $(locate 646.c | tail -n 1)