Difference between single and double square brackets in Bash

by

Single [] are posix shell compliant condition tests.

Double [[]] are an extension to the standard [] and are supported by bash and other shells (e.g. zsh, ksh). They support extra operations (as well as the standard posix operations). For example: || instead of -o and regex matching with =~. A fuller list of differences can be found in the bash manual section on conditional constructs.

Use [] whenever you want your script to be portable across shells. Use [[]] if you want conditional expressions not supported by [] and don’t need to be portable.

More Related Contents:

  1. Why should there be spaces around ‘[‘ and ‘]’ in Bash?
  2. How do I compare two string variables in an ‘if’ statement in Bash? [duplicate]
  3. Are double square brackets [[ ]] preferable over single square brackets [ ] in Bash?
  4. When are square brackets required in a Bash if statement?
  5. Is there a list of ‘if’ switches anywhere?
  6. Checking the success of a command in a bash `if [ .. ]` statement
  7. Test for non-zero length string in Bash: [ -n “$var” ] or [ “$var” ]
  8. Meaning of “[: too many arguments” error from if [] (square brackets)
  9. How to check the exit status using an ‘if’ statement
  10. Compound ‘if’ statements with multiple expressions in Bash
  11. Floating point comparison with variable in bash [duplicate]
  12. Using the && operator in an if statement
  13. How to do a logical OR operation for integer comparison in shell scripting?
  14. Bash if statement with multiple conditions throws an error
  15. Reading key/value parameters from a file into a shell script
  16. if, elif, else statement issues in Bash
  17. Validate date format in a shell script
  18. Groups of compound conditions in Bash test [duplicate]
  19. How to determine the current interactive shell that I’m in (command-line)
  20. Removing colors from output
  21. How to loop through a directory recursively to delete files with certain extensions
  22. Associative arrays in Shell scripts
  23. How can I remove the first line of a text file using bash/sed script?
  24. How to get the part of a file after the first line that matches a regular expression
  25. How can I reference a file for variables using Bash?
  26. How do I echo stars (*) when reading password with `read`?
  27. Bash: Copy named files recursively, preserving folder structure
  28. What does “export” do in shell programming? [duplicate]
  29. What is the most elegant way to remove a path from the $PATH variable in Bash?
  30. How to match a single quote in sed

Leave a Comment