SHELL

bash command substitution

# Basic syntax:
$(command)

# Example usage:
for file in $(ls)
do
  echo $file
done
--> # all files in your current directory are echoed

bash variable substitution

${!var}	#Just use to use reference value inside another variable ;)

bash substitution

## Bash Substitution - Search/Replace
${var#Pattern}
# Remove the shortest part of $Pattern that matches the front end of $var.
${var##Pattern} 
# Remove the longest part of $Pattern that matches the front end of $var.

${var%Pattern} 
# Remove the shortest part of $Pattern that matches the back end of $var
${var%%Pattern}
# Remove the longest part of $Pattern that matches the back end of $var

${var/Pattern/Replacement}
# Replace First match of Pattern
# If Replacement is omitted, the first match is replaced by nothing

${var//Pattern/Replacement}
# Global replacement. Replace All matches of Pattern
# if Replacement omitted, all occurrences of Pattern are replaced by nothing