Date: Mon, 7 Jul 2014 10:44:03 +0200 From: Polytropon <freebsd@edvax.de> To: Arthur Chance <freebsd@qeng-ho.org> Cc: FreeBSD Questions <freebsd-questions@freebsd.org> Subject: Re: The name "grep" Message-ID: <20140707104403.5a0694ff.freebsd@edvax.de> In-Reply-To: <53BA4F77.60907@qeng-ho.org> References: <20140707075443.d47ca06a.freebsd@edvax.de> <53BA4F77.60907@qeng-ho.org>
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On Mon, 07 Jul 2014 08:42:47 +0100, Arthur Chance wrote:
> From ancient memory circa 1980, probably suffering from bit rot:
>
> Before grep existed, to use ed to print lines in a file that match a
> particular regular expression
>
> ed $file
> g/re/p
> q
>
> where the "re" stands for the regular expression and you're applying the
> "p" (print) command to each line that matches it.
Yes, I already thought this was related to ed (discussed in the
same book at a previous occassion, and refered to as "the editor",
prior to introducing vi). So "r" and "e" aren't acutual commands
(p is a command, "print", g a modifier, "global"), but
refers to "put regular expression here".
Having another seizure that forced me to read "man ed", I found
some "re" entries:
(.,.)s/re/replacement/
(.,.)s/re/replacement/g
(.,.)s/re/replacement/n
\(re\)
The two important entries are:
(1,$)g/re/command-list
Apply command-list to each of the addressed lines matching a reg-
ular expression re. The current address is set to the line cur-
rently matched before command-list is executed. At the end of
the g command, the current address is set to the last line
affected by command-list
and
(.,.)p Print the addressed lines. The current address is set to the
last line printed.
There is the "re" of "g/re/p", leading to the understanding what
"grep" basically means (even though it offers much more functionality
as a stand-alone tool, of course).
> When a newbie asked how to print matching lines in a file, you'd answer
> "grep" and show them the trick, and eventually the name got given to the
> grep program when it was written. I think the "global regular expression
> print" explanation is based on explaining what the original ed command did.
And I have actually _tried_ that with /bin/ed - it works! So
should the "grep" manpage (and maybe other manpages, too)
contain a hint on where the program name originates from?
In my opinion, this would be a good place to put such kind
of information because manpages are a "condensed form" of
wisdom, available locally, for reference, study, and overall
education. Global Real Education, Pal. ;-)
--
Polytropon
Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...
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