shell scripting #

because i always forget these things.

most of these maybe arent posix shell compatible.

script options #

• set -u catch unbound variables
• set -e exit on error
• set -x verbose ‘debug’ output
• set -o pipefail exit when theres an error in a pipe
• i mostly use set -eu -o pipefail

by default bash doesnt expand aliases in scripts. fix:

shopt -s expand_aliases
alias sed=/usr/local/bin/sed-v48
# you can now just write sed instead of the full path to sed-v48

special variables #

• $1,$2,...$N the n-th cli argument. $0 is program name
• $@ cli args as array
• $? exit code of last command

templates #

switch case based on cli args

case $1 in
  ab)
    echo ab
    ;;
  bc)
    echo bc
    ;;
  *)
    echo default
    ;;
esac

for each loop

for elem in "${ARRAY[@]}"; do
  if XYZ; then
    echo hello
  fi
done

c style for loop

for (( i=0; i<${#ARRAY[@]}; i++ )); do
	printf "[%d] %s\n" "$i" "${ARRAY[$i]}"
done

map something to an array

mapfile -t results <<< $(curl domain.tld | grep | sed | sort)

bashisms #

until [run this command]; do
  [run this if command crashes]
done # command is restarted after running inner body