Re: a sed question

From	John-Paul Stewart <jpstewart@personalprojects.net>
Newsgroups	comp.unix.shell
Subject	Re: a sed question
Date	2024-12-18 15:12 -0500
Message-ID	<lsgokrFfuscU1@mid.individual.net> (permalink)
References	<874j304vv3.fsf@example.com>

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On 2024-12-18 2:46 p.m., Salvador Mirzo wrote:
> (*) Summary
> 
> I wrote a sed script that makes a line replacement after it finds the
> right spot.  So far so good.  Then I added quit command after the
> change, but the quit does not seem to take effect---violating my
> expectation.  I'll appreciate any help on understanding what's going on.
[snip]
> So far so good.  I decided to try it on longer files and I wanted to see
> the change more quickly (without long files scrolling past my terminal),
> so I decided to add a /q/ command right after the c commmand.  I
> thought---it will make sed quit right after making the change, so I can
> see it works as desired and then I remove the /q/ and release it to
> production.  But that did not happen.
[snip]
> I failed the exercise I gave myself.  Can you help me to understand why
> the q command isn't stopping sed as I thought it would?  I'd like to get
> a better intuition.

By default sed prints the "pattern space", i.e. all lines in the file.
You can suppress that with the "-n" option to sed.  (In other words, use
"sed -n" instead of plain "sed" in your script.)

The man page for GNU sed 4.9 says about the "q" command:

"Immediately quit the sed script without processing any more input,
except that if auto-print is not disabled the current pattern space will
be printed."

So the behaviour you're seeing without the "-n" option is to be
expected:  pattern space still gets auto-printed after the "q" command.

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a sed question Salvador Mirzo <smirzo@example.com> - 2024-12-18 16:46 -0300
  Re: a sed question John-Paul Stewart <jpstewart@personalprojects.net> - 2024-12-18 15:12 -0500
  Re: a sed question Ralf Damaschke <rwspam@gmx.de> - 2024-12-19 01:14 +0000
    Re: a sed question Salvador Mirzo <smirzo@example.com> - 2024-12-19 09:05 -0300
      Re: a sed question Ralf Damaschke <rwspam@gmx.de> - 2024-12-20 00:55 +0000
        Re: a sed question gazelle@shell.xmission.com (Kenny McCormack) - 2024-12-20 12:44 +0000
          Re: a sed question Ralf Damaschke <rwspam@gmx.de> - 2024-12-21 00:17 +0000
            Re: a sed question Kaz Kylheku <643-408-1753@kylheku.com> - 2024-12-21 03:09 +0000
              sed... (Was: a sed question) gazelle@shell.xmission.com (Kenny McCormack) - 2024-12-21 03:36 +0000
                Re: sed... (Was: a sed question) Kaz Kylheku <643-408-1753@kylheku.com> - 2024-12-21 03:57 +0000
                Re: sed... (Was: a sed question) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-21 15:38 +0100
                Re: sed... (Was: a sed question) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-21 17:29 +0100
                Re: sed... Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-12-21 14:23 -0800
                Re: sed... Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-22 00:33 +0100
                Re: sed... (Was: a sed question) Lars Poulsen <lars@cleo.beagle-ears.com> - 2024-12-21 21:46 +0000
                Re: sed... (Was: a sed question) Kaz Kylheku <643-408-1753@kylheku.com> - 2024-12-22 21:22 +0000
              Re: a sed question Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-21 15:35 +0100
              Re: a sed question Ralf Damaschke <rwspam@gmx.de> - 2024-12-22 00:43 +0000
  Re: a sed question Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-20 15:55 +0100
    Checking for right # of args in a shell script (Was: a sed question) gazelle@shell.xmission.com (Kenny McCormack) - 2024-12-20 15:11 +0000
      Re: Checking for right # of args in a shell script (Was: a sed question) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-20 16:49 +0100
        Re: Checking for right # of args in a shell script (Was: a sed question) gazelle@shell.xmission.com (Kenny McCormack) - 2024-12-20 17:43 +0000
    Re: a sed question Salvador Mirzo <smirzo@example.com> - 2024-12-21 09:17 -0300
      Re: a sed question Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-21 16:19 +0100
        Re: a sed question Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-12-21 13:41 -0800
          Re: a sed question Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-22 00:50 +0100
            Re: a sed question Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-12-21 16:26 -0800
              Re: a sed question Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-22 01:41 +0100
            Re: a sed question Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-12-22 00:31 +0000
              Re: a sed question Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-22 02:06 +0100
      Re: a sed question Andy Walker <anw@cuboid.co.uk> - 2024-12-21 15:34 +0000
        Re: a sed question Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-21 17:14 +0100
        Re: a sed question Salvador Mirzo <smirzo@example.com> - 2024-12-21 15:21 -0300
          Re: a sed question Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-21 20:48 +0100
      Re: a sed question Helmut Waitzmann <nn.throttle@xoxy.net> - 2024-12-21 19:20 +0100
    Re: a sed question Ordatious <order@order.invalid> - 2024-12-22 09:19 +0000
      Re: a sed question Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-22 19:23 +0100
  Re: a sed question Ed Morton <mortonspam@gmail.com> - 2024-12-21 08:13 -0600
    Re: a sed question Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-12-21 21:09 +0000
      Re: a sed question Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-22 01:02 +0100
        Re: a sed question Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-12-22 00:28 +0000
          Re: a sed question Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-12-21 16:36 -0800
            Re: a sed question Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-12-22 01:52 +0000
              Re: a sed question Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-12-21 21:09 -0800
                Re: a sed question Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-12-22 05:56 +0000
                Re: a sed question Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-12-21 22:55 -0800
                Re: a sed question Eric Pozharski <apple.universe@posteo.net> - 2024-12-23 10:09 +0000
                Re: a sed question gazelle@shell.xmission.com (Kenny McCormack) - 2024-12-23 12:41 +0000
                Re: a sed question Kaz Kylheku <643-408-1753@kylheku.com> - 2024-12-23 18:47 +0000
                Re: a sed question Eric Pozharski <apple.universe@posteo.net> - 2024-12-24 11:20 +0000
          Re: a sed question Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-22 02:22 +0100
      Re: a sed question gazelle@shell.xmission.com (Kenny McCormack) - 2024-12-22 01:09 +0000
      Re: a sed question Kaz Kylheku <643-408-1753@kylheku.com> - 2024-12-22 20:03 +0000
      Re: a sed question Ed Morton <mortonspam@gmail.com> - 2024-12-23 07:26 -0600
        How to solve The Miracle (was Re: a sed question) Janis Papanagnou <janis_papanagnou+ng@hotmail.com> - 2024-12-23 21:09 +0100
        Re: a sed question Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-12-23 22:57 +0000
          Re: a sed question Keith Thompson <Keith.S.Thompson+u@gmail.com> - 2024-12-23 15:06 -0800
            Re: a sed question Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-12-24 00:28 +0000
              Re: a sed question anthk <anthk@openbsd.home> - 2025-03-23 09:45 +0000
                Re: a sed question Lawrence D'Oliveiro <ldo@nz.invalid> - 2025-03-23 23:41 +0000
          Re: a sed question Ed Morton <mortonspam@gmail.com> - 2024-12-24 06:20 -0600
            Dealing with four-year-olds... (Was: a sed question) gazelle@shell.xmission.com (Kenny McCormack) - 2024-12-24 12:58 +0000
            Re: a sed question Lawrence D'Oliveiro <ldo@nz.invalid> - 2024-12-24 20:57 +0000
              Re: a sed question Kaz Kylheku <643-408-1753@kylheku.com> - 2024-12-24 21:46 +0000
                Arguing with a four-year-old (Was: a sed question) gazelle@shell.xmission.com (Kenny McCormack) - 2024-12-24 23:53 +0000

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