The short-circuiting in bash

Bash script writing is a import approach to configure the linux system. Suppose we wish to add a user if not exists, the command may seems as follow:

if (! id -u $TARGET_USER > /dev/null 2>&1 ); then
    echo "creating user $TARGET_USER"
    # adduser $TARGET_USER

However, it is kind of too long. In this case short-circuiting is a alternative solution. (more…)