Things you can do with bash

bash-tricks.sh

# Looping per line of input
some | command | sequence | while read var1 var2; do
  # something here
done

# Reading a file line by line
while read var1 var2 etc; do 
  perform --commands --with $var1 $var2 $etc
done < some-file.ext

# The for loop with test syntax
for f in *; do 
  if [[ -d "$f" ]]; then
    pushd "$f";
    echo "Do work";
    popd;
  fi; 
done

# Test for a pattern match
[[ $some-var =~ ^(some|regex)$ ]] && echo "Yep, it's a match!"

# Process substitution: http://tldp.org/LDP/abs/html/process-sub.html
cat <(what magic is this?)

# Load an array with data
# http://unix.stackexchange.com/questions/99423/appending-to-same-array-in-various-loops-only-last-values-remain-bash-4
some_array=()
while some test; do
  some_array+=("$some_variable")
done < <(some command producing output)

# if __name__ == '__main__': equivalent
if [[ ${BASH_SOURCE[0]} != $0 ]]; then
  # We were sourced, not run
else
  # We are being run, go, go, go!
fi

commands.sh

# Useful command sequences

# Find the first command that is defined
# For example, this uses the GNU brew-installed utilities before the normal readline on Mac
# while on a system without it (or Linux it will use the normal readline)
type -p greadlink readlink | head -1

# Alter a remote's URL
git remote -v | cut -d' ' -f 1 | cut -f 1-2 | sed 's/something/something-else/g' | xargs -t -n 2 git remote set-url;

# Run sed on a set of files containing a pattern
grep -rl matchstring somedir/ | xargs sed -i 's/string1/string2/g'

# Run sed with alternative delimiters (any character will work)
sed 's_http://some/url_http://some/replacement_g'

script-example.sh

#!/usr/bin/env bash -f

shopt -s extglob

SCRIPT_NAME=`basename $0`

read -rd '' HELP << HELP
$SCRIPT_NAME - what the script does

Usage:

$SCRIPT_NAME
  [-a|--option-a A]             - the first option
                                  (default: some sensible default)
  [-b|--option-b B]             - another option
                                  Falls back on \$SOME_SYSTEM_VARIABLE
  positional-args ...           - A longer description
                                  spanning several lines


Examples:
* $SCRIPT_NAME -a an -b example           # With a description
HELP

[[ $# -lt 1 ]] && echo "$HELP" && exit 1;

option_a=
option_b="$SOME_SYSTEM_VARIABLE"

function opt() {
  echo "-$1?(=*)|--$2?(=*)"
}

# See https://argbash.dev/ for more patterns
while [ "${1+defined}" ]; do
  case $1 in
    -h|--help) echo "$HELP" && exit 0;;
    # Simple options
    -a|--option-a) option_a="$2"; shift;
    # Options that support being called with =
    -b?(=*)|--option-b?(=*)) if [[ "$1" = *=* ]];
      then option_b="${1#*=}";
      else option_b="$2"; shift;
    fi;;
    # Using code to define actual pattern (requires shopt -s extglob)
    @($(opt c chatty))) echo "Will chat now" && exit 0;;
    -d|--option-d) option_d=on;;
    # Allow getopts-style collections of short args
    # This will allow -de and -ed to both parse correctly
    -d*) _rest="${1##-d}"; set -- "-d" "-$_rest" "$@";;
    -e|--option-e) option_e=on;;
    -e*) _rest="${1##-e}"; set -- "-e" "-$_rest" "$@";;
    *) echo "Unknown option $1" >&2 && exit 1;;
  esac
  shift
done

echo "$option_a and $option_b"