On Tue, Jun 05, 2012 at 10:17:47PM +0200, Michael Schwendt wrote:
On Tue, 05 Jun 2012 12:35:34 -0700, jdow wrote:On 2012/06/05 11:55, Michael Schwendt wrote: > On Tue, 5 Jun 2012 14:40:23 -0400, Alex wrote: > >> It's used in shell scripts, such as an "if" statement, such as "if [ >> $? -eq 0 ]". Bash actually runs that command. > > Not Bash. > > $ type [ > [ is a shell builtin > > Also see "man [". > $ type /usr/bin/[ /usr/bin/[ is /usr/bin/[Of course. What are you trying to prove? Bash doesn't run that command. "man test" explains it, too: | NOTE: your shell may have its own version of test and/or [, which usu‐ | ally supersedes the version described here. Please refer to your | shell's documentation for details about the options it supports. -- Fedora release 17 (Beefy Miracle) - Linux 3.3.7-1.fc17.x86_64 loadavg: 1.78 1.58 1.44 -- users mailing list users@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe or change subscription options: https://admin.fedoraproject.org/mailman/listinfo/users Guidelines: http://fedoraproject.org/wiki/Mailing_list_guidelines Have a question? Ask away: http://ask.fedoraproject.org
### End of Message from Michael Schwendt ### I hope this puts the issue to bed:An unadorned '[' in bash (or borne sh, or zsh, and probably others) actually is a built-in command. This speed tests tremendously by preventing execing every time a test needs to be performed.
For some ancient shells test (a.k.a. '/usr/bin/[') was an external command. It is still provided for backwards compatibility.
In bash you *can* use it, so long as you either call it long-hand: $ /usr/bin/\[ -n "$var" ] But it would be stupid to do so.Every once in a while, you might encounter a program that execs your commands directly, i.e. *not* in a shell. IIRC, Udev RUN= and PROGRAM== are examples of these. If you want to test something, then you would have to use something like:
PROGRAM=="bash -c '[ "$a" -eq "$b" ]'This is clumsy*. Because you have /usr/bin/\[ in the path, you could probably get away with:
PROGRAM=='[ "$a" -eq "$b" ]'* ok, it's not completely fair to call this clumsy, because when you run bash, you also get all your functions, aliases and other built-ins, so oftentimes it actually *is* better to use 'bash -c'.
HTH -- ×-×-×-×-×-×-×-×-×-×-× Jeffrey A. Gipson ×-×-×-×-×-×-×-×-×-×-×
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