Foreach & file io

Xxaxx has asked for the wisdom of the Perl Monks concerning the following question:

With your help I'd like to double check my understanding of how foreac works with file io.

foreach my $line (<$INFILE>) {
     ## do stuff
}
[download]

As far as I know the above snippet will read a single line at a time during processing.

I'm guess I'm just checking to make sure it doesn't try reading the whole file into a temporary array and then feed the array elements to the foreach.

Is that correct? Claude

Comment on Foreach & file io Download Code

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Re: Foreach & file io by jeroenes (Priest) on Jun 05, 2001 at 14:00 UTC
It all depends on what you did to $/, see perlvar. If you leave that alone, your script always will read single lines with the `for my $line (<INFILE>)` or `my $line=<INFILE>;` syntax. Beware, though, that fileGLOBs are written as `open IN, $file;`. Your $INFILE will work on a variable, that's not what you (probably) want. (Update Unless you pass a reference to a fileGLOB :-). I would use lowercase here though, to take away possible confusion with real fileGLOBs and constants. Try $fh_infile, eg.) Cheers, Jeroen "We are not alone"(FZ)	[reply] [d/l] [select]
Re: Re: Foreach & file io by Xxaxx (Monk) on Jun 05, 2001 at 14:22 UTC
Thanks the perlvar was the piece that solved the puzzle. Seems like no matter how many times I read that thing I only remember the stuff I have a need for before I read it. Thanks again Claude p.s. the $INFILE is actually correct since I'm opening my file in a subroutine then returning *FH.	[reply]
(tye)Re: Foreach & file io by tye (Sage) on Jun 05, 2001 at 19:10 UTC
By default, `<>` will read one line at a time. However, foreach builds up the list before iterating over it so the above code will read the entire file into memory and then start iterating over the lines. For this type of thing you are much better off using while. - tye (but my friends call me "Tye")	[reply] [d/l]
Re: (tye)Re: Foreach & file io by Xxaxx (Monk) on Jun 05, 2001 at 22:04 UTC
Thanks tye, Based on the program's timing that is what it felt like. Hence checking with fell monks for the scoop. Much appreciated. Back to the while. Claude	[reply]


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