QUERY ABOUT A SECTION OF A CODE

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

Can someone please explain what this section of the codes means especially for %h, my $file = 'file'.$pixel.'.jpg' and unlink $file or die $! if -e $file. Thanks

 my %h = (
    '500x500'   => 505544,
    '750x750'   => 1118012,
    '1000x1000' => 1986284,
    '1500x1500' => 4468241,
    '2000x2000' => 7907740,
);

my $pixel = '1000x1000';
my $url_file = 'http://speedserver/file'.$pixel.'.jpg';
my $file = 'file'.$pixel.'.jpg';

unlink $file or die $! if -e $file;
[download]

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Re: QUERY ABOUT A SECTION OF A CODE by aaron_baugher (Curate) on May 16, 2012 at 20:50 UTC
The first statement creates a hash variable and assigns a group of keys and values to it. The second statement assigns a value to the scalar variable `$pixel`. The third statement assigns a value to the scalar variable `$url_file`, concatenating two string values and the value of `$pixel`. The fourth statement assigns a value to the scalar variable `$file`, again concatenating two bits of text with the value of `$pixel`. The fifth statement is the most complicated one. It says, "if the file named in `$file` exists, `unlink` (delete) the file or exit the program and tell me the most recent error." Using `or` in this way is an idiomatic way in Perl to say, "do this, and if it fails, do that." So if the `unlink` succeeds, the `or` is satisfied and the `die` is not executed. To rewrite it longhand to make the order of things clearer: `if( -e $file ){ unless( unlink $file ){ die $!; } }` [download] Aaron B. Available for small or large Perl jobs; see my home node.	[reply] [d/l] [select]
Re: QUERY ABOUT A SECTION OF A CODE by snape (Pilgrim) on May 16, 2012 at 20:39 UTC
%h is hash table. $file is a scalar variable and contains file name and unlink $file, deletes the file. `my $file = 'file'.$pixel.'.jpg';` It means that $file = file1000x1000.jpg (is a string type). It concatenates the strings i.e. file, value in $pixel and .jpg as one string. Concatenation You need to read about perl first and then ask questions: perldoc, learn Perl	[reply] [d/l]
Re: QUERY ABOUT A SECTION OF A CODE by choroba (Cardinal) on May 17, 2012 at 10:16 UTC
Crossposted at Stackoverflow. It is considered polite to inform about crossposting so people not visiting both sites do not waste their time in solving a problem already solved at the other site.	[reply]
Re^2: QUERY ABOUT A SECTION OF A CODE by majo (Novice) on May 20, 2012 at 22:14 UTC
I am sorry about that.	[reply]