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For example, the following Perl one-liner will reverse all the bytes in a file: perl -0777e 'print scalar reverse <>' filename While most Perl one-liners are imperative, Perl's support for anonymous functions, closures, map, filter (grep) and fold (List::Util::reduce) allows the creation of 'functional' one-liners.
A module defines its source code to be in a package (much like a Java package), the Perl mechanism for defining namespaces, e.g. CGI or Net::FTP or XML::Parser; the file structure mirrors the namespace structure (e.g. the source code for Net::FTP is in Net/FTP.pm).
(Note that, on Microsoft Windows systems, Perl programs are typically invoked by associating the .pl extension with the Perl interpreter. In order to deal with such circumstances, perl detects the shebang line and parses it for switches. [4]) The second line in the canonical form includes a semicolon, which is used to separate statements in Perl.
In these languages, including the line __DATA__ (Perl) or __END__ (Ruby, old Perl) marks the end of the code segment and the start of the data segment. Only the contents prior to this line are executed, and the contents of the source file after this line are available as a file object: PACKAGE::DATA in Perl (e.g., main::DATA) and DATA in Ruby ...
#!usr/bin/perl – called the "shebang line", after the hash symbol (#) and ! (bang) at the beginning of the line. It is also known as the interpreter directive. # – the number sign, also called the hash symbol. In Perl, the # indicates the start of a comment. It instructs perl to ignore the rest of the line and not execute it as script code.
Perl Programming Documentation, also called perldoc, is the name of the user manual for the Perl 5 programming language. It is available in several different formats, including online in HTML and PDF. The documentation is bundled with Perl in its own format, known as Plain Old Documentation (pod).
Perl Compatible Regular Expressions (PCRE) is a library written in C, which implements a regular expression engine, inspired by the capabilities of the Perl programming language. Philip Hazel started writing PCRE in summer 1997. [ 3 ]
The placeholder may be a variable name, or in some languages an arbitrary expression, in either case evaluated in the current context. String interpolation is an alternative to building string via concatenation , which requires repeat quoting and unquoting; [ 2 ] or substituting into a printf format string , where the variable is far from where ...