Bash is the default shell environment for most modern Linux distributions. While the differences between different shell environments are minimal if you are not a power user, Bash has extended functionality. Any executable in your $PATH environment variable can be used as a Bash command, and referencing an executable outside of $PATH will execute it by default. While Bash has very complete documentation, this post will demonstrate a few hacks and common usage patterns for bash scripting.

Argument parsing

while [ $# -gt 0 ]; do
    case "$1" in
        -h | --help)     usage;;
        -a | --arg1)     ARG1="$2"; shift 2;;
        -b | --arg2)     ARG2="$2"; shift 2;;
        -e | --flag1)    FLAG1=1; shift;;
        *)               usage "$1";;
    esac
done

One-liner fizzbuzz

seq 100 | awk '$0=$1%15?$1%5?$1%3?$1:"Buzz":"Fizz":"FizzBuzz"'

Text processing

grep

Print only lines that contain the given sequence

• -A 7: print the matching lines and the following 7 lines after each occurrence.
• -B 7: same as above but before
• -P: use Perl-style regex

sed

sed 's/foo/bar/g' file.txt

Find foo and replace with bar

awk

The following prints the entry points for all processes running under your user

ps -ux | awk '{print $11}'

And this prints the number of each processes under each entry point

ps -ux | awk '{print $11}' | awk '{count[$0]++} END {for (line in count) print count[line], line}' | sort -nr