The Perl Shrine

My Favorite Perl One-Liners

# Reverse a string
perl -e 'print scalar reverse "Hello World\n"'

# Find duplicate lines in a file
perl -ne 'print if $seen{$_}++' file.txt

# In-place find and replace
perl -pi -e 's/foo/bar/g' *.txt

# Print lines matching a pattern (better grep)
perl -ne 'print if /^\d{3}-\d{4}/' contacts.txt

# One-liner web server (the original)
perl -MIO::Socket::INET -e '$s=IO::Socket::INET->new(LocalPort=>8080,Listen=>5,Reuse=>1);while($c=$s->accept){print $c "HTTP/1.0 200 OK\r\n\r\nIt works!\n";close $c}'

Perl Error Message Hall of Fame

Lepercum's Laws of Perl Debugging

Debug or Die()

        +--------------+
        | Script fails |
        +------+-------+
               |
        +------v-------+
        |  Add print   |
        |  statements  |
        +------+-------+
               |
        +------v-------+     YES    +-------------+
        | Does it work +----------->| Remove half |
        |    now?      |            | the prints, |
        +------+-------+            | ship it     |
               | NO                 +-------------+
        +------v-------+
        | Try          |
        | Data::Dumper |
        +------+-------+
               |
        +------v-------+     YES    +-------------+
        | Understand   +----------->|    Liar.    |
        | the output?  |            +-------------+
        +------+-------+
               | NO
        +------v-------+
        |   perl -d    |
        +------+-------+
               |
        +------v-------+     YES    +-------------+
        | Fixed it?    +----------->| Mass email  |
        |              |            | the team    |
        +------+-------+            +-------------+
               | NO
        +------v-------+
        | Ask on       |
        | PerlMonks    |
        +------+-------+
               |
        +------v-------+     YES    +-------------+
        | Was it a     +----------->| It's always |
        | missing      |            | a missing   |
        | semicolon?   |            | semicolon.  |
        +------+-------+            +-------------+
               | NO
        +------v-------+
        |    die()     |
        +--------------+

Larry Wall Quotes

• "We all agree on the necessity of compromise. We just can't agree on when it's necessary to compromise."
• "A Perl program is correct if it gets the job done before your straitened boss fires you."
• "I think the way most people do programming, they do it in a way that's like trying to write a novel by writing one line at a time."
• "The three chief virtues of a programmer are: Laziness, Impatience, and Hubris."

Top 10 CPAN Modules I Trust With My Life

1. DBI - Talks to databases without making me write C every time. ★★★★★
2. CGI.pm - The gateway drug that let half the web accept form submissions. ★★★★★
3. LWP::UserAgent - Fetches web pages so my scripts can pretend to be productive. ★★★★★
4. Data::Dumper - When the variables lie, this one tells the truth. ★★★★★
5. Storable - Freezes Perl data structures for later regret and retrieval. ★★★★☆
6. File::Find - Crawls a directory tree like a bloodhound with shell access. ★★★★☆
7. Text::CSV - Because spreadsheets will always find a way into production. ★★★★☆
8. Template::Toolkit - Keeps HTML mostly separate from Perl, which everyone appreciates. ★★★★☆
9. Net::FTP - The reason deployment can happen from a motel room at 1 AM. ★★★☆☆
10. Getopt::Long - Makes command-line scripts look like they were planned. ★★★★☆