Working on the basis of $! is "russian-roulette" with you guaranteed to lose everytime, it's value can be anything when the expression it is associated with succeeds. 
$ perl -le 'print $c++ for 0..0xFFFF' > test; ls -l test
-rwxr-xr-x 1 user user 382106 2006-11-14 15:04 test

$ perl -e 'open F, "test"; print "$! => $_" while <F>'
Bad file descriptor => 0
Bad file descriptor => 1
Bad file descriptor => 2
...

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Infact, undefining $! has no effect and perlvar does say "the value of $! is meaningful only immediately after a failure". Like $^E, its useful for one thing only - describing the error that occured. Programming around it would definitely be considered "bad practice".

Just use defined or eval to test the success of readline(). 
#!/usr/bin/perl -Wl
use strict;
use warnings;

$|++;

open F, "<", $ARGV[0];

while (1) {
    last if  eof(F);
    if (defined chomp( local $_ = readline (F) )) {
        print
    } else {
        warn "hmerrm, readline failed : $!";
        last;
    }
}

# or

while (1) {
    last if  eof(F);
    chomp( local $_ = eval "readline (F)" );
    unless ($@) {
        print;
    } else {
        warn "whoops, readline failed : $@";
        last;
    }
}

[download]

In reply to Re: Best way to handle readline errors? by Firefly258
in thread Best way to handle readline errors? by jrw

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