Perl – Rob Allen's DevNotes

Prefixing every key in a hash ref in Perl

I needed to prepend some text to every element in a Perl hash ref, so I came up with:

$hashref->{"prefix_$_"} = delete($hashref->{$_}) foreach (keys %$hashref);

1	$hashref->{"prefix_$_"} = delete($hashref->{$_}) foreach (keys %$hashref);

which prefixes each key of $hashref with "prefix_". After talking it over with Cliff, he was concerned with modifying the list in place while simultaneously iterating over it and suggested this solution:

%$hashref = map { +"prefix_$_" => $hashref->{$_} } keys %$hashref;

1	%$hashref = map { +"prefix_$_" => $hashref->{$_} } keys %$hashref;

One interesting thing about this solution is the requirement for a unary "+" in map in order to help Perl work out… continue reading.

Posted on 8 July 2014 in Perl

Missing mime-info database for use with File::MimeInfo

A requirement I have on a current project means that I need to determine the mime type of a file I load from disk. One way to do this is to use the File::MimeInfo::Magic CPAN module like this:

use File::MimeInfo::Magic;
my $mime_type = mimetype($path_to_file);

1 2	use File::MimeInfo::Magic; my $mime_type = mimetype($path_to_file);

However, on OS X, an error was raised: WARNING: You don't seem to have a mime-info database. The shared-mime-info package is available from http://freedesktop.org/ . The easiest way to solve this is via Homebrew:

$ brew install shared-mime-info
$ update-mime-database /usr/local/share/mime

1 2	$ brew install shared-mime-info $ update-mime-database /usr/local/share/mime

Posted on 2 June 2014 in Perl

Category: Perl

Prefixing every key in a hash ref in Perl

Missing mime-info database for use with File::MimeInfo

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