test

Evaluate condition. If it is true, returns 0 exit status, otherwise returns 1.

Test if given variable is equal to given string:

test $MY_VAR == '/bin/zsh'

Test if given variable is empty:

test -z $GIT_BRANCH

Test if file exists:

test -e {{filename}}

Test if directory not exists:

test ! -d {{path/to/directory}}

If-else statement:

test {{condition}} && echo "true" || echo "false"