What does “grep” stand for? (was: Regular expressions)

[Ben Finney]

Steven D'Aprano <steve+comp.lang.python at pearwood.info> writes:

> On Wednesday 04 November 2015 13:55, Dan Sommers wrote:
>
> > Its very name indicates that its default mode most certainly is
> > regular expressions.
>
> I don't even know what grep stands for. 

“grep” stands for ‘g/RE/p’.

The name is a mnemonic for a compound command in ‘ed’ [0], a text editor
that pre-dates extravagant luxuries like “presenting a full screen of
text at one time”.


In an ‘ed’ session, the user is obliged to keep mental track of the
current line in the text buffer, and even what that text contains during
the session.

Single-letter commands, with various terse parameters such as the range
of lines or some text to insert, are issued at a command prompt one
after another.

For these reasons, the manual page describes ‘ed’ as a “line-oriented
text editor”. Everything is done by specifying lines, blindly, to
commands which then operate on those lines.

The name of the ‘vi’ editor means “visual interface (to a text editor)”,
to proudly declare the innovation of a full screen of text that updates
content during the editing session. That was not available for users of
‘ed’.


A very common command to issue, then, is “actually show me the line of
text I just specified”; the ‘p’ (for “print”) command.

Another very common command is “find the text matching this pattern and
perform these commands on it”, which is ‘g’ (for “global”). The ‘g’
command addresses text matching a regular expression pattern, delimited
by slashes ‘/’.

So, for users with feeble human brains incapable of remembering
perfectly the entire content of the text while it changes and therefore
not always knowing exactly which lines they wanted to operate on without
seeing them all the time, a very frequent combination command is:

    g/RE/p

meaning “find lines forward from here that match the regular expression
pattern “RE”, and do nothing to those lines except print them to
standard output”.


Wikipedia has useful pages on both ‘grep’ and ‘ed’
<URL:https://en.wikipedia.org/wiki/Grep>
<URL:https://en.wikipedia.org/wiki/Ed_%28text_editor%29>.

You can see a full specification of how the ‘ed’ interface is to behave
as part of the “Open Group Base Specifications Issue 7”, which is the
specification for Unix.

    <URL:http://pubs.opengroup.org/onlinepubs/9699919799/utilities/ed.html>

See the manual for GNU ed which includes an example session to
appreciate just how far things have come.

    <URL:https://www.gnu.org/software/ed/manual/ed_manual.html#Introduction-to-line-editing>

Of course, if you yearn for the days of minimalist purity, nothing beats
Ed, man! !man ed


[0] The standard text editor.
    <URL:https://www.gnu.org/fun/jokes/ed-msg.txt>

-- 
 \     “If you can't annoy somebody there is little point in writing.” |
  `\                                                    —Kingsley Amis |
_o__)                                                                  |
Ben Finney