Bash Substitutions

Bash supports various constructs for substituting contents of variables.

Setting default values:

• Return on unset value: VAR=${VAR:-blarg}

• Assign on unset value: ${VAR:=blarg}

Substituting substring:

• First occurence: ${FILE/urs/usr}

• All occurences: ${FILE//urs/usr}

• At end of string: ${FILE/%.jpg/.png}

• At front of string: ${FILE/#${HOME}/~/}

Command substitutions:

• Either: pwd

• Or: $(pwd)

The latter is easier to nest:

• Either:

  `basename `pwd``
  

• Or: $(basename $(pwd))