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Raku rules are the regular expression, string matching and general-purpose parsing facility of the Raku programming language, and are a core part of the language. Since Perl's pattern-matching constructs have exceeded the capabilities of formal regular expressions for some time, Raku documentation refers to them exclusively as regexes, distancing the term from the formal definition.
In computing, command substitution is a facility that allows a command to be run and its output to be pasted back on the command line as arguments to another command. Command substitution first appeared in the Bourne shell , [ 1 ] introduced with Version 7 Unix in 1979, and has remained a characteristic of all later Unix shells .
The three-way comparison operator or "spaceship operator" for numbers is denoted as <=> in Perl, Ruby, Apache Groovy, PHP, Eclipse Ceylon, and C++, and is called the spaceship operator. [2] In C++, the C++20 revision adds the spaceship operator <=>, which returns a value that encodes whether the 2 values are equal, less, greater, or unordered ...
The regular-expression engine uses a backtracking algorithm, extending its capabilities from simple pattern matching to string capture and substitution. The regular-expression engine is derived from regex written by Henry Spencer. The Perl regular-expression syntax was originally taken from Unix Version 8 regular expressions.
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 ]
Here are examples in the Perl programming language: Look for duplicate words; perl -0777 -ne ' print "$.: doubled $_\n" while /\b(\w+)\b\s+\b\1\b/gi ' Find Palindromes in /usr/dict/words; perl -lne ' print if $_ eq reverse ' /usr/dict/words in-place edit of *.c files changing all foo to bar; perl -p -i.bak -e ' s/\bfoo\b/bar/g ' *.c Many one ...
Sed regular expressions, particularly those using the "s" operator, are much similar to Perl (sed is a predecessor to Perl). The default delimiter is "/", but any delimiter can be used; the default is s / regexp / replacement / , but s : regexp : replacement : is also a valid form.
Note that the C code under the CODE: section calls the _do_sv_catsv() pure-C function that was defined in the prior section. Perl’s documentation explains the meaning and purpose of all of the “special” symbols (e.g., aTHX_ and RETVAL) shown above. To make this module available to Perl it must be compiled.