Is double square brackets [[ ]] preferable over single square brackets [ ] in Bash?

Question

A co-worker claimed recently in a code review that the [[ ]] construct is to be preferred over [ ] in constructs like

if [ \"`id -         


        

Answer 1

If you are into following Google's style guide:

Test, [ and [[

[[ ... ]] reduces errors as no path name expansion or word splitting takes place between [[ and ]], and [[ ... ]] allows for regular expression matching where [ ... ] does not.

# This ensures the string on the left is made up of characters in the
# alnum character class followed by the string name.
# Note that the RHS should not be quoted here.
# For the gory details, see
# E14 at https://tiswww.case.edu/php/chet/bash/FAQ
if [[ "filename" =~ ^[[:alnum:]]+name ]]; then
  echo "Match"
fi

# This matches the exact pattern "f*" (Does not match in this case)
if [[ "filename" == "f*" ]]; then
  echo "Match"
fi

# This gives a "too many arguments" error as f* is expanded to the
# contents of the current directory
if [ "filename" == f* ]; then
  echo "Match"
fi