On Fri, 8 May 2009 16:10:20 +0200 Alan McKinnon <alan.mckin...@gmail.com> wrote:
> On Friday 08 May 2009 16:01:14 Mike Kazantsev wrote: > > > Some greps (like BSD one) might not support '--color' option, so "echo > > hello|grep --color=auto l" will return error code, skipping if clause, > > and won't break grep operation by adding an unsupported option. > > except that STDERR is combined with STDOUT and sent to /dev/null so the > script > will never get it, the if is always true and the entire check is redundant. > Better would be > > if echo hello|grep --color=auto l >/dev/null ; then As many ppl just pointed out, you mistake "output check" done by "[" or "test" commands with shell built-in "if" statement operation, which looks only to a given command exit code, doesn't bothering with any output. "if [ $A ]" is equivalent to "if test $A" (where "test" is "/usr/bin/test"), except that modern shells implement test command as a built-in. For the rest of them, there's actually "/usr/bin/\[" symlink, which should exist on your system as well. So what happens is "test $A", silently returning it's exit code to "if". And of course, you can use any command instead of "test". For example there's also "/bin/true" and "/bin/false", so idiomatical "if true" and "if false" would actually work as expected ;) -- Mike Kazantsev // fraggod.net
signature.asc
Description: PGP signature
