Path: utzoo!utgpu!watserv1!watmath!att!att!pacbell.com!ucsd!sdd.hp.com!uakari.primate.wisc.edu!crdgw1!sixhub!davidsen
From: davidsen@sixhub.UUCP (Wm E. Davidsen Jr)
Newsgroups: comp.unix.questions
Subject: Re: edit first line of long file
Message-ID: <2164@sixhub.UUCP>
Date: 24 Oct 90 03:12:36 GMT
References: <27338@shamash.cdc.com> <568@inews.intel.com> <4597:Oct2321:44:2190@kramden.acf.nyu.edu>
Reply-To: davidsen@sixhub.UUCP (bill davidsen)
Organization: *IX Public Access UNIX, Schenectady NY
Lines: 53

In article <4597:Oct2321:44:2190@kramden.acf.nyu.edu> brnstnd@kramden.acf.nyu.edu (Dan Bernstein) writes:

| > sed is the way.
| 
| No, it's not. Try head -1 | sed 's/.../.../'; cat.

  Okay, results below.

|                                                            On this
| machine, sed is more than 12 times slower than cat.

results:

Script started [y.tmp] at Tue Oct 23 23:03:14 1990
$ ls -l x.tmp
-rw-r--r--   1 davidsen users     143405 Oct 23 23:01 x.tmp
$ time cat x.tmp > /dev/null

real	0m0.50s
user	0m0.00s
sys	0m0.36s
$ time sed '1s/foo/bar/' x.tmp > /dev/null

real	0m2.20s
user	0m1.42s
sys	0m0.40s
$ time { head -1; sed 's/foo/bar/'; cat; } < x.tmp > /dev/null

real	0m3.16s
user	0m1.86s
sys	0m0.70s
$ exit
Script ended [y.tmp] at Tue Oct 23 23:05:28 1990

  How 'bout that! The overhead of all the other stuff made it slower. I
guess I'll vote for using just plain sed, because it's easier, faster,
uses less memory, etc. I didn't create a multi-megabyte file, so there
may be a break even point, but I wouldn't bet on it.

Other points:

  Yes, this was ksh, so the time reported is for all processes.
/bin/time would not do as well unless you started a subshell.

  Your 12:1 slower surprised the hell out of me, but you are definitely
in the right order of magnitude, perhaps even being a little nice to
sed. I really would have expected sed to just bypass the stuff after
line 1.
-- 
bill davidsen - davidsen@sixhub.uucp (uunet!crdgw1!sixhub!davidsen)
    sysop *IX BBS and Public Access UNIX
    moderator of comp.binaries.ibm.pc and 80386 mailing list
"Stupidity, like virtue, is its own reward" -me