Shell Tricks

Sometimes you can be just as productive using your shell as you are in any programming environment, you just need to know a couple of tricks. In this article, I’ll walk through some basic tips that I’ve come across.

Reading input

You can make your scripts immediately interactive by using the read instruction.

#/bin/bash

echo -n "What is your name? "
read NAME

echo "Hi there ${NAME}!"

String length

You can get the length of any string that you’ve stored in a variable by prefixing it with #.

#/bin/bash

echo -n "What is your name? "
read NAME

echo "Your name has ${#NAME} characters in it"

Quick arithmetic

You can perform some basic arithmetic within your scripts as well. The value emitted with the # character is an integral value that we can perform tests against.

#/bin/bash

echo -n "What is your name? "
read NAME

if (( ${#NAME} > 10 )) 
then
  echo "You have a very long name, ${NAME}"
fi

Substrings

String enumeration will also allow you to take a substring directly. The format takes the form of ${VAR:offset:length}.

Passing positive integers for offset and length will make substring operate from the leftmost side of the string. Negative numbers provide a reverse index, from the right.

STR="Scripting for the win"

echo ${STR:10:3}
# for

echo ${STR: -3}
# win

echo ${STR: -7: 3}
# the

Replacement

It’s common place to be able to use regular expressions to make substitutions where needed, and they’re available to you at the shell as well.

#!/bin/bash

STR="Scripting for the win"

echo ${STR/win/WIN}
# Scripting for the WIN

Finishing up

There’s lots more that you can do just from the shell, without needing to reach for other tools. This is only a few tips and tricks.