while loop hanging

Patrick2003 has asked for the wisdom of the Perl Monks concerning the following question:

If anyone can help,that'll be super. I'm no expert to programming and new to Perl. I'm trying to do 2 main simple things. 1 - Count the rows of an input file and print the count, and 2 - print each row in sequence. It works when I run these 2 scripts separately, but not together as followed:

test(); 
sub test {
    $count = 0;
    $count++ while (<>);
    print "COUNT = $count";
    
    while (<>) {
        chomp;
        print $_."\n";
    }
}
[download]

Comment on while loop hanging Download Code

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Re: while loop hanging by no_slogan (Deacon) on Jan 31, 2003 at 18:30 UTC
a) This has the look of homework. b) The second while loop is not hung, it is trying to read from standard input. The magic <> operator consumes @ARGV, you see.	[reply]
Re: while loop hanging by insensate (Hermit) on Jan 31, 2003 at 20:47 UTC
`use strict; print $.,"\n",my @f=<>;` [download]	[reply] [d/l]
Re: while loop hanging by Anonymous Monk on Jan 31, 2003 at 19:02 UTC
`$ cat yourfile \| wc -l ; cat yourfile` [download] If you are on a win32 system get cygwin or gnu power tools.	[reply] [d/l]
Re: while loop hanging by dbp (Pilgrim) on Jan 31, 2003 at 19:10 UTC
Why don't you think about combining the loops into one. It seems to me that it would be pretty easy to increment your counter every time you print out a line...	[reply]
Re: Re: while loop hanging by Patrick2003 (Initiate) on Jan 31, 2003 at 19:47 UTC
I thought about that, but I want the total count of rows at the very beginning of my output. Thanks	[reply]
Re: Re: Re: while loop hanging by Hofmator (Curate) on Jan 31, 2003 at 20:29 UTC
OK, so combining this together with no_slogan's advise that the magic `while(<>)` consumes @ARGV, you need to store @ARGV before the first loop and restore it after the first loop is done. `my @old_ARGV = @ARGV; my $count; $count++ while <>; print "COUNT = $count\n"; @ARGV = @old_ARGV; print while <>;` [download] And as you see, it's a bit pointless to first chomp off the newline if you add it later again in the print - so I removed that. You could make good use of local here as well, but I leave that as an exercise for the reader ... :) -- Hofmator	[reply] [d/l] [select]