file handles and file input

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

I am currently playing around with a Perl script which is supposed to read lines of text from files, chomp, then chop them, and then print the output to an output file. Only problem is, is that the script is starting at the second line in the (input) text file, and skipping every other line. Here is the code...

#!/usr/bin/perl

my $filestring = $ARGV[0];

my $outfile_str = "$ARGV[1]"."_new";

open(IN, "<$filestring");
open(OUT, ">$outfile_str");

my $string_parser;

while(<IN>){
   $string_parser = <IN>;
   print "$string_parser";
   chomp $string_parser;
   chop $string_parser;
   print OUT "$string_parser ";
   }
   
close(IN);
close(OUT);

Any ideas?
[download]

Comment on file handles and file input Download Code

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Re: file handles and file input by kyle (Abbot) on Feb 12, 2008 at 20:35 UTC
The problem is that `while(<IN>)` reads a line of the file (and puts it into `$_`), and `$string_parser=<IN>` also reads a line from the file. Try this instead: `while ( $string_parser = <IN> ) { print "$string_parser"; # ... }` [download]	[reply] [d/l] [select]
Re: file handles and file input by pc88mxer (Vicar) on Feb 12, 2008 at 20:38 UTC
The `while (<IN>)` is reading a line from the file (and placing the result in `$_`) and then you are reading yet another line with `$string_parser = <IN>;` So that's why `$string_parser` is being set to every other line.	[reply] [d/l] [select]
Re: file handles and file input by GrandFather (Saint) on Feb 12, 2008 at 20:38 UTC
Try: `while(my $string_parser = <IN>) {` [download] instead of `while(<IN>)` which reads a line into $_, then `$string_parser = <IN>` which reads the next line into $string_parser - effectively throwing away the previous line. Perl is environmentally friendly - it saves trees	[reply] [d/l] [select]
Re: file handles and file input by sh1tn (Priest) on Feb 12, 2008 at 21:35 UTC
Use perldoc -q when in doubt. perldoc -q file and perldoc -f readline in this case.	[reply]
Re^2: file handles and file input by FunkyMonk (Chancellor) on Feb 12, 2008 at 22:29 UTC
You can even type `[doc://readline]` (etc) into the search box on any PerlMonks page. `[perldoc://file]` will search the perlfaqs. See What shortcuts can I use for linking to other information? for more details.	[reply] [d/l] [select]
Re^3: file handles and file input by sh1tn (Priest) on Feb 13, 2008 at 00:06 UTC
Unless I prefer cli pod access to http one. Otherwise nice point.	[reply]
Re^4: file handles and file input by softworkz (Monk) on Feb 13, 2008 at 16:23 UTC
Re: file handles and file input by Anonymous Monk on Feb 12, 2008 at 21:18 UTC
Oops!!! Sorry about that!!!	[reply]