parameter-substitution.bash

#!/bin/bash

# Cheatsheet for remembering Bash rules for Parameter Substitution:
# https://tldp.org/LDP/abs/html/parameter-substitution.html#PSUB2


# Fallback for unset vars

# Bash    #——> like JavaScript
${a+b}    #——> a && b
${a-b}    #——> a || b
${a?b}    #——> a || (print(b), exit(1))
${a=b}    #——> a ||= b
#  ^—————————> use colon prefix (i.e. :- := :+ :?) for null instead of unset


# String replacing

${a/b/c}  #——> replace one
${a//b/c} #——> replace all

${a/#b/c} #——> replace at beginning
${a/%b/c} #——> replace at end

${a#b}    #——> remove match from beginning (## for greedy)
${a%b}    #——> remove match from end (%% for greedy)


# String length and substring

${#a}     #——> string length
${a:b}    #——> substring start
${a:b:c}  #——> substring start and len