Bash snippets

bash_snippets.sh

#!/bin/bash

## Debugging: Show expanded commands before executing them
set -x

## Debugging: Exit with error on attempt to use unset variable
set -u

## Run commands in subshell
( /bin/foo; /bin/bar )

## Check command result
/bin/foo bar baz
if [ $? -ne 0 ]; then              # Note: Don't leave out the spaces: they are significant
    echo "foo returned result $?"
    exit 1
else
    echo "foo was cool"
fi

## Or, more compactly
if ! /bin/foo bar baz; then echo "foo returned $?"; exit 1; fi

## Set environment variable if not already set
if [ -z "$MYVAR" ]; then export MYVAR="fiddledy dee"; fi

## Create directory if it does not exist
if [ ! -d "$MYDIR" ]; then /bin/mkdir -p "$MYDIR"; fi

## Send output to stdout and to log file
/bin/foo 2>&1 | tee foo.log

## Do something for each file in a directory
for f in $( ls ); do echo $f; done

## Function
foo ()
{
    echo "foo was called with arguments: $1 $2"
}
foo hello world

Used in this blog entry: http://undefinedvalue.com/2012/06/23/bash-scripting-cheatsheet