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

[princepawn]

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

[antirice]

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.

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

[chromatic]

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

[pbeckingham]

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.