While idly reading the Camel (3rd edition) I noticed on page 99 that if you do a stat or file test on a file, then you can do more tests on the same file using _ as Perl caches the initial file test - thus reducing the number of system calls Perl has to make.

Thus you can do: 

if (-e $file && -T _) {
    print "foo";
}

[download]
instead of the more obvious, though slower: 
if (-e $file && -T $file) {
    print "bar";
}

[download]

I was quite inpressed with this, indeed it's mentioned again in chapter 24. I tried some tests this morning, and using the underscore is quite a bit faster on my Wintel box, than separate tests.

I've never seen this construct before, though it's easy enough to miss, and even though I've seen it now it's hard to search for an underscrore like this, as underscore is used in some many other places.

Q1 Does anybody actually use this construct? I don't recall seeing it in any books, though I've just this minute found it in the excellent Effective Perl Programming

Q2 What other little tricks like this have I missed? I know there are many things I must have missed, so this question is like asking how long is a piece of string, but what are peoples favourite coding constructs that are "cool" but uncommon

As ever, thanks in advance...

In reply to Does anyone use underscore pseudo-filehandle? by ajt

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