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  1. #1

    If Else Variable Notation (SHELL SCRIPT)

    What's the difference between

    (A) if [ $1 = 1 ]; then...


    (B) if [ "$1" = 1 ]; then...


    (C) if [ "$1" -eq 1 ]; then...

    and which one is the correct notation?

  2. #2
    For (A), [ $1 = 1 ] is just wrong. First of all, if you are comparing strings, you should use ==, not =. Single = should be reserved for variable assignment. If you are comparing strings, you should also put quotes around the right-hand side value.

    Same goes with (B), except that the double-quotes around "$1" will preserve spaces in the argument. Also use the quotes on the right hand side, e.g.:
     if [ "$1" == '1' ]
    For (C), it is assumed you are comparing numbers, by virtue of the -eq, therefore, you don't need the quotes aournd the $1, e.g.:
     if [ $1 -eq 1 ]
    I leave it to you to decide what is right, as it is based upon what you are trying to do (comparing strings vs numbers, etc.).

  3. #3
    Linux Engineer hazel's Avatar
    Join Date
    May 2004
    Harrow, UK
    "=" is an operator that tests equality in strings. "-eq" tests it for integers. I think for equality, the two would actually work the same, but for some inequalities, they wouldn't. For example 10 -gt 2 but "10" < "2".

    Putting quotes round a variable simply ensures that, if the value contains a space or some other special character, it won't cause problems.
    @atreyu: I think it is "=" in bash, "==" in C.
    "I'm just a little old lady; don't try to dazzle me with jargon!"

  4. $spacer_open
  5. #4
    I guess they're both considered okay. According to the bash manpage:
           string1 == string2
                  True  if  the  strings  are  equal.   = may be used in place of == for
                  strict POSIX compliance.
    i usually just read the first sentence. :P

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