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In the Perl programming language, grep is a built-in function that finds elements in a list that satisfy a certain property. [16] This higher-order function is typically named filter or where in other languages. The pcregrep command is an implementation of grep that uses Perl regular expression syntax. [17]
grep is a command-line utility for searching plain-text data sets for lines matching a regular expression and by default reporting matching lines on standard output. tree is a command-line utility that recursively lists files found in a directory tree, indenting the filenames according to their position in the file hierarchy.
The split function returns a list of strings, which are split from a string expression using a delimiter string or regular expression. @scores = split ( ',' , '32,45,16,5' ); Individual elements of a list are accessed by providing a numerical index in square brackets.
He later added this capability to the Unix editor ed, which eventually led to the popular search tool grep's use of regular expressions ("grep" is a word derived from the command for regular expression searching in the ed editor: g/re/p meaning "Global search for Regular Expression and Print matching lines"). [15]
Many Unix utilities are line-oriented. These may work with xargs as long as the lines do not contain ', ", or a space. Some of the Unix utilities can use NUL as record separator (e.g. Perl (requires -0 and \0 instead of \n), locate (requires using -0), find (requires using -print0), grep (requires -z or -Z), sort (requires using -z)).
/R Uses search strings as regular expressions. /S Searches for matching files in the current directory and all subdirectories. /I Specifies that the search is not to be case-sensitive. /X Prints lines that match exactly. /V Prints only lines that do not contain a match. /N Prints the line number before each line that matches.
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. This one-liner creates a function that can be used to return a list of primes up to the value of the first parameter:
where the output from the grep process (all lines containing 'blair') is piped to the more process (which allows a command line user to read through results one page at a time). The same "pipe" feature is also found in later versions of DOS and Microsoft Windows.