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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