Question

In Bash script, what is the difference between the following snippets?

1) Using single brackets:

if [ "$1" = VALUE ] ; then
 # code
fi

2) Using double brackets:

if [[ "$1" = VALUE ]] ; then
 # code
fi

Answer 1

The [[ ]] construct is the more versatile Bash version of [ ]. This is the extended test command, adopted from ksh88.

Using the [[ … ]] test construct, rather than [ … ] can prevent many logic errors in scripts. For example, the &&, ||, <, and > operators work within a [[ ]] test, despite giving an error within a [ ] construct.

More info on the Advanced Bash Scripting Guide.

In your snippets, there’s no difference as you’re not using any of the additional features.