Re: Naming file handles with variables?

I think this will do what you want. It handles any number of files to be opened and the sub-routine will return at each iteration a reference to an array holding the next line of each of these files. When all files are exhausted it returns undef

use strict;

my @filenames = qw/one.txt two.txt three.txt/;
my @filehandles;

foreach my $filename (@filenames) {
    open my $fh, '<', $filename or die "Could not open $filename; $!";
    push @filehandles, $fh;
} ## end foreach my $filename (@filenames)

while (1) {
    my $lines_ref = read_lines_parallel(@filehandles);
    last unless $lines_ref;
    print join '|', @$lines_ref;
    print '-' x 20, "\n";
} ## end while (1)

sub read_lines_parallel {
    my @filehandles = @_;
    my @lines;
    foreach (@filehandles) {
        push @lines, scalar <$_>;
    } ## end foreach (@filehandles)
    if ( join '', @lines ) {
        return \@lines;
    } ## end if ( join '', @lines )
    else {
        return undef;
    } ## end else [ if ( join '', @lines )
} ## end sub read_lines_parallel
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Output:

first line file 1
|line 1 file 2
|first line file 3
--------------------
second line file 1
|line 2 file 2
|second line file 3
--------------------
third line file 1
||third line file 3
--------------------
||fourth line file 3
--------------------
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Update: I do not know what herbs I put in my tea when I wrote something as ugly as

while (1) {
    my $lines_ref = read_lines_parallel(@filehandles);
    last unless $lines_ref;
    print join '|', @$lines_ref;
    print '-' x 20, "\n";
}
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Obviously it should be

while (my $lines_ref = read_lines_parallel(@filehandles)) {
    # Do something with $lines_ref or @$lines_ref here
    print join '|', @$lines_ref;
    print '-' x 20, "\n";
}
[download]

CountZero

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James

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