Bash Parameter Expansion

bash Parameter Expansion

P is evaluated
V is the argument

${P+V}

${P-V}

${P=V}

${P?V}

P is not set

V

P = V

V > stderr

P is set

V

P

P

P

${P:+V}

${P:-V}

${P:=V}

${P:?V}

P is not set or is null

V

P = V

V > stderr

P is set and not null

V

P

P

P

exit if interactive shell