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Re: Perl Idioms Explained - my $string = do { local $/; <FILEHANDLE> };

by princepawn (Parson)
on Aug 29, 2003 at 17:55 UTC ( #287778=note: print w/ replies, xml ) Need Help??

in reply to Perl Idioms Explained - my $string = do { local $/; <FILEHANDLE> };

I like:

my $slurp = join '', <FH>;

Carter's compass: I know I'm on the right track when by deleting something, I'm adding functionality... download and use The Emacs Code Browser

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Re: Re: Perl Idioms Explained - my $string = do { local $/; <FILEHANDLE> };
by antirice (Priest) on Aug 29, 2003 at 20:31 UTC

    A couple of things. First and foremost, don't you think that ought to be:

    my $slurp = join $/, <FH>;

    Otherwise you can't really distinguish between lines. Next, you're having perl read the file in, split the file on $/, and then rejoin everything and you end up with a string that was exactly what it was before the split. If you just localize $/ and then read the file in, you're done. Of course, I have some nice benchmarks that show the local $/ method to be a little under 5 times faster. As with any other benchmarks, YMMV.

    #!/usr/bin/perl -w use Benchmark qw(cmpthese); # file.txt is about 2200 lines each between 5 and 50 chars long open FH, "file.txt" or die $!; sub scalarcon { seek(FH,0,0); local $/; <FH>; } sub listjoin { seek(FH,0,0); join '',<FH>; } cmpthese(-5,{scalarcon=>\&scalarcon,listjoin=>\&listjoin}); __DATA__ Benchmark: running listjoin, scalarcon for at least 5 CPU seconds... listjoin: 5 wallclock secs ( 5.25 usr + 0.12 sys = 5.38 CPU) @ 30 +.70/s (n=165) scalarcon: 6 wallclock secs ( 1.95 usr + 3.36 sys = 5.30 CPU) @ 15 +3.26/s (n=813) Rate listjoin scalarcon listjoin 30.7/s -- -80% scalarcon 153/s 399% --

    Update: As chromatic has pointed out, I'm a twit.

    Hope this helps.

    The first rule of Perl club is - use Perl
    ith rule of Perl club is - follow rule i - 1 for i > 1

      Your first suggestion would seem to double the input record separator. Did you test it? Do you somehow have autochomp enabled?

      #!/usr/bin/perl -w use strict; my $line = join $/, <DATA>; print "<<$line>>\n"; __DATA__ one two tie my shoe
Re: Re: Perl Idioms Explained - my $string = do { local $/; <FILEHANDLE> };
by pbeckingham (Parson) on Mar 10, 2004 at 19:01 UTC
    I have been using
    my $slurp = join '', <FH>;
    as well, but having had the idiom explained to me, I realize that this approach is potentially doing more work than the idiom. It makes sense to me that reading from a file handle in list context causes a list to be returned, which is then collapsed by the join, and that this approach is probably not as efficient.

    I assume that the idiom is achieving this down in the (fast) IO layer, and the cost of the block, and the localized variable are lower.

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