Editing Perl (section)

=== Syntax ===

Perl has been referred to as "[[wikt:line noise|line noise]]" and a "write-only language" by its critics. [[Randal L. Schwartz]] in the first edition of the book ''[[Learning Perl]]'',<ref>{{cite journal |title=Developer Update|volume=2 |journal=Dr. Dobb's Developer Update |publisher=Miller-Freeman |year=1995 |page=15}}</ref> in the first chapter states: {{qi|Yes, sometimes Perl looks like line noise to the uninitiated, but to the seasoned Perl programmer, it looks like [[checksum]]med line noise with a mission in life.<ref name="LP">{{cite book |title=Learning Perl |last=Schwartz |first=Randal L. |author-link=Randal L. Schwartz |publisher=O'Reilly & Associates |year=1993 |title-link=Learning Perl |bibcode=1993lepe.book.....S}}</ref>|i=yes}} He also stated that the accusation that Perl is a [[write-only language]] could be avoided by coding with "proper care".<ref name="LP"/> The Perl overview document ''{{Not a typo|perlintro}}'' states that the names of built-in "magic" scalar [[Variable (computer science)|variables]] "look like punctuation or line noise".<ref>{{cite web |url=http://perldoc.perl.org/perlintro.html |title=perlintro |work=Perl 5 version 18.0 documentation |publisher=Perl 5 Porters and perldoc.perl.org |access-date=2013-06-30 |archive-url=https://web.archive.org/web/20110109121845/http://perldoc.perl.org/perlintro.html |archive-date=January 9, 2011 |url-status=dead}}</ref> However, the English module provides both long and short English alternatives. ''{{Not a typo|perlstyle}}'' document states that line noise in [[regular expression]]s could be mitigated using the <code>/x</code> modifier to add whitespace.<ref>{{cite web |url=http://perldoc.perl.org/perlstyle.html |title=perlstyle |work=Perl 5 version 18.0 documentation |publisher=Perl 5 Porters and perldoc.perl.org |access-date=2013-06-30 |archive-url=https://web.archive.org/web/20130626010707/http://perldoc.perl.org/perlstyle.html |archive-date=June 26, 2013 |url-status=dead}}</ref>

According to the ''Perl 6 FAQ'',<ref name="P6FAQ">{{cite web |url=http://www.perl6.org/archive/faq.html |title=Perl 6 FAQ |publisher=Perl 6 Project |access-date=2013-06-30 |archive-date=July 1, 2013 |archive-url=https://web.archive.org/web/20130701183900/http://www.perl6.org/archive/faq.html |url-status=dead}}</ref> Perl 6 was designed to mitigate "the usual suspects" that elicit the "line noise" claim from Perl 5 critics, including the removal of "the majority of the punctuation variables" and the sanitization of the regex syntax. The ''Perl 6 FAQ'' also states that what is sometimes referred to as Perl's line noise is "the actual syntax of the language" just as [[gerund]]s and [[Preposition and postposition|prepositions]] are a part of the [[English language]].<ref name="P6FAQ"/> In a December 2012 blog posting, despite claiming that "Rakudo Perl 6 has failed and will continue to fail unless it gets some adult supervision", [[chromatic (programmer)|chromatic]] stated that the design of Perl 6 has a "well-defined grammar", an {{qi|improved type system, a unified object system with an intelligent [[metamodel]], metaoperators, and a clearer system of context that provides for such niceties as pervasive laziness.<ref name="chromatic-blog">{{cite web |url=http://www.modernperlbooks.com/mt/2012/12/the-implementation-of-perl-5-versus-perl-6.html |title=The Implementation of Perl 5 versus Perl 6 |author1=chromatic |author1-link=chromatic (programmer) |date=2012-12-31 |access-date=2013-06-30 |archive-date=July 29, 2013 |archive-url=https://web.archive.org/web/20130729214209/http://www.modernperlbooks.com/mt/2012/12/the-implementation-of-perl-5-versus-perl-6.html |url-status=live}}</ref>|i=yes}} He also stated that {{qi|Perl 6 has a coherence and a consistency that Perl 5 lacks.<ref name="chromatic-blog"/>|i=yes}}

In Perl, one could write the [["Hello, World!" program]] as:

<syntaxhighlight lang="perl">
print "Hello, World!\n";
</syntaxhighlight>

Here is a more complex Perl program, that counts down seconds from a given starting value:

<syntaxhighlight lang="perl">
#!/usr/bin/env perl
use strict;
use warnings;

my ( $remaining, $total );

$remaining=$total=shift(@ARGV);

STDOUT->autoflush(1);

while ( $remaining ) {
    printf ( "Remaining %s/%s \r", $remaining--, $total );
    sleep 1;
}

print "\n";
</syntaxhighlight>

The Perl interpreter can also be used for [[One-liner program|one-off scripts]] on the [[command line]]. The following example (as invoked from an sh-compatible shell, such as [[Bash (Unix shell)|Bash]]) translates the string "Bob" in all files ending with .txt in the current directory to "Robert":

<syntaxhighlight lang="console">
$ perl -i.bak -lp -e 's/Bob/Robert/g' *.txt
</syntaxhighlight>