The actions will be much the same, but the way it works is rather different: foreach takes a list, which means that before the loop starts the whole of the input file is read, building a list of lines on perl's internal stack and then iterating over that list.

while, on the other hand, reads one line at a time and performs the block on that line before reading the next line. This can use far less memory, and so is usually preferable.

Good question. foreach my $line(<INFILE>){} reads the entire file into an anonymous array, aliasing each element in turn to $line. while (my $line = <INFILE>){} reads the file one line at a time, storing each in turn in $line.

The foreach version must allocate more memory than the while loop, which is a bit slower. The tradeoff is up to you.

Update: ++chromatic points out that foreach iterates over a list, not an anonymous array.

After Compline,
Zaxo

Thanks, I suspected as much, but wanted to make sure. In the code, the loop actually just appends $line to a string, so I suspect the effect of the foreach is not what the author had in mind.

That's what people call a 'slurp'. There's many ways to do it and if you search PerlMonks for 'slurp' you'll find them. Here's one I cooked up earlier:

# FILE is already open ...
{
   local $/ = undef;
   $slurp = <FILE>;
}
[download]

Much better (and faster) than using joins, or loops to append. Keep it inside the {} block so that the change to $/ is only temporary. (also see $/ at perldoc). The file's entire content ends up in $slurp.

#!perl

use strict;

my $ln = 9;
my $contents;

open (Fnm , "a.dat");

while ($contents = <Fnm>){
     chomp;
     if ($ln == 9){
         close Fnm;
         $ln = 0;
     }
     print "[ $contents ]\n";
}
__END__
[ one 
 ]
[download]

#!perl

use strict;

my $ln = 9;
my $contents;

foreach $contents(<Fnm>){

    chomp;
    if ($ln == 9){
       close Fnm;
       $ln = 0;
    }
    print "[ $contents ]\n";

}
__END__
[ one
 ]
[ next
 ]
[ next
 ]
[ next
 ]
[ next
 ]
[download]