Bash Scripting¶

Iterate over a file ¶

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

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

Another way of writing is this:

#!/bin/bashwhile read p; do    echo  $pdone

For-loops ¶

#!/bin/bashfor ((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/bashfor x in `seq 1 100`; do    echo $xdone

If statement ¶

$1 here represent the first argument.

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

If/Else ¶

#!/bin/bashif [ "$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/bashfor 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/bashlocate 646.c | tail -n 1

This can be done like this:

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