[[ ]] test always reports a "not found" error in bash shell scrip t

[Randall R Schulz]

Michael,

At 09:21 2003-06-26, MATTHEWS,MICHAEL (HP-Vancouver,ex1) wrote:
>Thu 2003/JUN/26 0921 PDT
>
>Hello,
>
>I am porting a Linux build system to Windows XP by using the Cygwin 1.3.22-1
>environment (see the attached text file for output from "cygcheck -s -v
>-r"). All of the bash shell scripts use the [[ ]] test in if statements,
>similar to:
>
>   if [[ "$(uname -s)" != "Linux" ]]
>   then
>     # Do Cygwin stuff
>   else
>     # Do Linux stuff
>   fi
>
>Whenever I run the script in the Cygwin bash shell, the conditional
>executes, but the following error is displayed in the terminal window:
>
>   [[: not found

My guess is that your scripts begin with something like this:

#!/bin/sh

Under cygwin, this invokes ash, not BASH.


>If I replace the double square brackets with single square brackets:
>
>   if [ "$(uname -s)" != "Linux" ]
>   then
>     # Do Cygwin stuff
>   else
>     # Do Linux stuff
>   fi
>
>I do not get any error message.
>
>I use the [[ ]] test because from what I read about the bash shell
>conditional testing, using [[ ]] is better than [ ], since [[ ]] is tested
>internally, whereas [ ] is tested in a separate shell with the "test"
>command. I would prefer to not have to change all of the test conditionals
>in our Linux bash shell scripts from [[ ]] to [ ].


Background information from my Cygwin:

BASH_VERSINFO=([0]="2" [1]="05b" [2]="0" [3]="9" [4]="release" 
[5]="i686-pc-cygwin")
BASH_VERSION='2.05b.0(9)-release'

% bash --version
GNU bash, version 2.05b.0(9)-release (i686-pc-cygwin)
Copyright (C) 2002 Free Software Foundation, Inc.

% help [
[: [ arg... ]
     This is a synonym for the "test" builtin, but the last
     argument must be a literal `]', to match the opening `['.
[[ ... ]]: [[ expression ]]
     Returns a status of 0 or 1 depending on the evaluation of the conditional
     expression EXPRESSION.  Expressions are composed of the same 
primaries used
     by the `test' builtin, and may be combined using the following operators

         ( EXPRESSION )  Returns the value of EXPRESSION
         ! EXPRESSION    True if EXPRESSION is false; else false
         EXPR1 && EXPR2  True if both EXPR1 and EXPR2 are true; else false
         EXPR1 || EXPR2  True if either EXPR1 or EXPR2 is true; else false

     When the `==' and `!=' operators are used, the string to the right of the
     operator is used as a pattern and pattern matching is performed.  The
     && and || operators do not evaluate EXPR2 if EXPR1 is sufficient to
     determine the expression's value.


Two things are germane here:

1) [[ ... ]] _is_ available in Cygwin BASH (of course).

2) The distinction between [ ... ] and [[ ... ]] is not what you seem 
to think it is. In particular, they're both BASH built-ins.


>I checked the versions of bash in Cygwin and in Linux and they are:
>
>   Cygwin bash version : GNU bash, version 2.05b.0(9)-release
>(i686-pc-cygwin)
>   Linux bash version  : GNU bash, version 2.05b.0(1)-release
>(i686-pc-linux-gnu)
>
>The version of Linux we are using is Red Hat 8.0 Linux.
>
>
>-Michael


Randall Schulz 


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