Shell equality operators (=, ==, -eq)

by

It’s the other way around: = and == are for string comparisons, -eq is for numeric ones. -eq is in the same family as -lt, -le, -gt, -ge, and -ne, if that helps you remember which is which.

== is a bash-ism, by the way. It’s better to use the POSIX =. In bash the two are equivalent, and in plain sh = is the only one guaranteed to work.

$ a=foo
$ [ "$a" = foo ]; echo "$?"       # POSIX sh
0
$ [ "$a" == foo ]; echo "$?"      # bash specific
0
$ [ "$a" -eq foo ]; echo "$?"     # wrong
-bash: [: foo: integer expression expected
2

(Side note: Quote those variable expansions! Do not leave out the double quotes above.)

If you’re writing a #!/bin/bash script then I recommend using [[ instead. The doubled form has more features, more natural syntax, and fewer gotchas that will trip you up. Double quotes are no longer required around $a, for one:

$ [[ $a == foo ]]; echo "$?"      # bash specific
0

See also:

More Related Contents:

  1. Correct Bash and shell script variable capitalization
  2. While loop stops reading after the first line in Bash
  3. How can I compare numbers in Bash?
  4. Pipe output and capture exit status in Bash
  5. Redirect stderr and stdout in Bash [duplicate]
  6. Why equal to operator does not work if it is surrounded by space?
  7. Which characters need to be escaped when using Bash?
  8. How do I run a shell script without using “sh” or “bash” commands?
  9. How can I suppress all output from a command using Bash?
  10. Assignment of variables with space after the (=) sign?
  11. How to get a password from a shell script without echoing
  12. Exit Shell Script Based on Process Exit Code [duplicate]
  13. How can I use Bash syntax in Makefile targets?
  14. Pass all variables from one shell script to another?
  15. Delete files older than 10 days using shell script in Unix [duplicate]
  16. Checking if output of a command contains a certain string in a shell script
  17. Bash conditional based on exit code of command
  18. Simulating ENTER keypress in bash script
  19. How to make awk ignore the field delimiter inside double quotes? [duplicate]
  20. Passing arguments by reference
  21. Get just the filename from a path in a Bash script [duplicate]
  22. Rename multiple files in shell [duplicate]
  23. Is there a way to make bash job control quiet?
  24. Get current directory or folder name (without the full path)
  25. Execute a shell function with timeout
  26. Convert Unix timestamp to a date string
  27. Using Bash to display a progress indicator (spinner) [duplicate]
  28. When does command substitution spawn more subshells than the same commands in isolation?
  29. Extract version number from a string
  30. Subtract two variables in Bash

Leave a Comment