Bash_Tricks.md

Bash script template

# This script template was copied from https://gist.github.com/ErezBinyamin/132c576b132f397ae63f7059d72ff5c9
# Save this script as some unique SCRIPTNAME.sh
# For starters rename the 'SCRIPTNAME' variable: `sed -i s/SCRIPTNAME/desiredname/g`

SCRIPTNAME() {
  # Argparsing envars and positional arguments into meaningfully named local variables. Don't do optargs in bash scripts
  local ENVAR=${ENVAR:-defaultValueString}
  local ARG1=${1:-7}
  [[ $# -lt 0 || $# -gt 3 ]] && return 1
  
  helperFunction() {
    echo "Incremented ARG1 from ${ARG1} to $((ARG1++))"
    export ARG1
  }
  
  # Main
  helperFunction
  return 0
}
# Run if called with `bash SCRIPTNAME.sh`, Do not run if called by `source SCRIPTNAME.sh`
[[ "$0" =~ "SCRIPTNAME.sh" ]] && SCRIPTNAME $@

Variable Expansion

There are some lesser known bash variable expansions:

description	expression
Remove everything after the last '7'	${var%7*}
Remove everything after the first '7'	${var%%7*}
Remove everything before the first '7'	${var#*7}
Remove everything before the last '7'	${var## *7}
First char upper case	${var^}
All upper case	${var^^}
First char lower case	${var,}
All lower case	${var,,}
Show how variable was set	${var@A}
?? something cool ??	${var@E}
Print variable as though it were the prompt variable PS1	${var@P}
?? something cool ??	${var@Q}

I have been struggling to find a source that documents all of these tricks. So far the best one I have found is curl cheat.sh/bash/:learn. But even that page is missing these expansion rules.

ErezBinyamin/Bash_Tricks.md

Bash script template

Variable Expansion