code working fine on Perl 5.12.1 doesn't work on 5.10.0

I wrote some code (about 100 lines) that is working fine on version 5.12.1. Unfortunately my client is using version 5.10.0. So I tested the code on 5.10.0 and found it doesn't work!

Where can I find a list of differences between 5.10 and 5.12?

Edit:

I think the best answer to the question of "Where can I find a list of differences between 5.10 and 5.12" is plusplus开发者_Go百科' comment under the "accepted answer". For the explanation of the code below, please read Michael Carman's answer.

The code that works on 5.12.1 but does not work on 5.10.0 ($contents is still an empty string after running the code)

# read in the first 10 lines.
my $contents = '';
for (my $i = 0; $i < 10 && ! eof; $i++) {
    $contents .= <FILE>;
}

The improved code that works on both versions.

# read in the first 10 lines.
my $contents = '';
my $i = 0;
while (<FILE>) {
    last if $i >= 10;
    $contents .= $_;
    $i++;
} 

There's a bug in your first code sample. A bare eof reports status for the last filehandle read. On of the first pass through the loop you (presumably) haven't read anything yet; not anything from FILE anyway. It appears that the internal behavior of this invalid call changed. Under Perl 5.12.1 running perl -E "say eof" prints nothing. Under Perl 5.10.0 it prints "1".

Explicitly testing eof(FILE) should fix the problem.

Tangent: Your code isn't very idiomatic. A more perlish approach would be

my $content;
while(<$fh>) {
    if ( 1 .. 10 ) { $content .= $_ }
    else           { last }
}

The idioms used are:

• Use a lexical filehandle instead of a typeglob. ($fh instead of FILE)
• Use the range operator .. to track the number of lines read. This form implicitly tests against the input line number $..
• Don't explicitly test for EOF (let the loop handle it).
• Use last to break out of the loop early.

Look at the perldoc page. You''ll find the perldelta's there. Or post your code and have us look at it ;)