shell scripting

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
    echo ab
    echo bc
    echo default

for each loop

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

c style for loop

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

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