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grep is a command-line utility for searching plaintext datasets for lines that match a regular expression. Its name comes from the ed command g/re/p (global regular expression search and print), which has the same effect.
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.
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]
NOTE: An application using a library for regular expression support does not necessarily support the full set of features of the library, e.g., GNU grep uses PCRE, but supports no lookahead, though PCRE does.
In computing, tree is a recursive directory listing command or program that produces a depth-indented listing of files. Originating in PC- and MS-DOS, it is found in Digital Research FlexOS, [1] IBM/Toshiba 4690 OS, [2] PTS-DOS, [3] FreeDOS, [4] IBM OS/2, [5] Microsoft Windows, [6] and ReactOS.
PCRE can use a large recursive stack with corresponding high memory usage and result in exponential runtime on certain patterns. In contrast, RE2 uses a fixed stack size and guarantees that its runtime increases linearly (not exponentially) with the size of the input. The maximum memory allocated with RE2 is configurable.
This mutually recursive definition can be converted to a singly recursive definition by inlining the definition of a forest: t: v [t[1], ..., t[k]] A tree t consists of a pair of a value v and a list of trees (its children). This definition is more compact, but somewhat messier: a tree consists of a pair of one type and a list another, which ...
Sets the path to be searched for data files or displays the current search path. The APPEND command is similar to the PATH command that tells DOS where to search for program files (files with a .COM, .