[[ and ]] are not portable. [ and ] are portable and specified in POSIX. Like if you always use [[ and ]] you are going to be surprised when the default shell

[[ and ]] are not portable. [ and ] are portable and specified in POSIX. Like if you always use [[ and ]] you are going to be surprised when the default shell used for running unattended scripts in Debian, Ubuntu refuses to run your script. dash: 1: [[: not found I know your parent commenter mentioned "#!/bin/bash" so your point is still valid. But I recommend that always use "#!/bin/sh" and always use [ and ] so that the scripts are portable. I say this as a former package maintainer who has spent a great deal of time converting Bash scripts to POSIX sh scripts just so that I can package them as .deb.