Re: capturing command output

[moritz]

I'm pretty sure it does involve a shell; what other part should take care of the redirection 2>&1?

And I don't think it's any better than backticks. It also lacks proper error handling.

[Eliya]

what other part should take care of the redirection 2>&1?

Perl itself?  Like it does on Unix when 2>&1 is the only shell meta characters in the command.^*

I don't think Perl is making this optimisation on Windows, though, but I do think it's a valid question — considering that in Perl things are not always quite as obvious as it might seem at first...

___

^* as you can easily verify:

$ strace -fqeexecve perl -e 'open FH, "echo foo bar 2>&1 |"; print <FH
+>'
execve("/usr/bin/perl", ["perl", "-e", "open FH, \"echo foo bar 2>&1 |
+\"; "...], [/* 77 vars */]) = 0
[pid  1819] execve("/bin/echo", ["echo", "foo", "bar"], [/* 77 vars */
+]) = 0
foo bar

No shell involved here.  But as soon as you add another shell metacharacter, e.g. ";", Perl will use the shell:

$ strace -fqeexecve perl -e 'open FH, "echo foo bar ; 2>&1 |"; print <
+FH>'
execve("/usr/bin/perl", ["perl", "-e", "open FH, \"echo foo bar ; 2>&1
+ |\""...], [/* 77 vars */]) = 0
[pid  1833] execve("/bin/sh", ["sh", "-c", "echo foo bar ; 2>&1"], [/*
+ 77 vars */]) = 0
foo bar

[chrestomanci]

Very interesting. ++

I had no idea that perl did that optimization, it is good to know, but it would be nice to have a way to control it.

[Eliya]

but it would be nice to have a way to control it.

You can already (indirectly) control it — at least in the direction of forcing the use of the shell.  Just add a dummy ";" to the command (which should always be possible without changing the semantics).  Or simply call sh -c "..." yourself.

(And be sure to add a comment regarding the ";", or else the next maintainer might remove that seemingly superfluous character again... :)