Re: a sed question

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Sujet : Re: a sed question
De : janis_papanagnou+ng (at) *nospam* hotmail.com (Janis Papanagnou)
Groupes : comp.unix.shell
Date : 20. Dec 2024, 15:55:12
Autres entêtes
Organisation : A noiseless patient Spider
Message-ID : <vk40gi$3g9sm$1@dont-email.me>
References : 1
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On 18.12.2024 20:46, 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.

First (before I forget it) change your string comparison '<' to the
numerical comparison operator '-lt' as in:   test $# -lt 2 && usage
Otherwise, if you get used to using the wrong operator, you may get
subtle errors in future if you continue that habit.

Also note that using  $*  may not work correctly (e.g. depending on
filenames [containing spaces] used). The safe form is a quoted  "$@"

(Then I was tempted to make a similar comment as Kenny. But...)

WRT your question I'd be interested to understand more about the
intention of your original question...

I mean if you don't trust your 'sed' command just pipe it though
'less'; there's no need to change the 'sed' program just for that.

Personally I'd try whether it works (by adding "something" before
and also after the desired place in your sample.txt to be sure the
other occurrences were not changed), and then just call

  sed -e '/<<Release>>=/,+1s/something/sth else/'  sample.txt

to see it working.

Janis

 
(*) A detailed description
 
I wrote this program:
 
--8<-------------------------------------------------------->8---
%cat make-release
#!/bin/sh
usage()
{
  printf '%s tag file\n' $0
  exit 1
}
test $# '<' 2 && usage
tag="$1"
shift
sed "/<<Release>>=/ {
 n;
 c\
$tag
}" $*
--8<-------------------------------------------------------->8---
 
Here's how I use it.  My objective with it is to replace that
/something/ in the text file with a new argument.
 
--8<-------------------------------------------------------->8---
%cat sample.txt
Lorem ipsum dolor...
 
<<Release>>=
something
@
 
... sit a met [...]
%
--8<-------------------------------------------------------->8---
 
Here's how I invoke it:
 
--8<-------------------------------------------------------->8---
%sh make-release release1 sample.txt
Lorem ipsum dolor...
 
<<Release>>=
release1
@
 
... sit a met [...]
--8<-------------------------------------------------------->8---
 
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.
 
--8<-------------------------------------------------------->8---
%cat make-release
#!/bin/sh
usage()
{
  printf '%s tag file\n' $0
  exit 1
}
test $# '<' 2 && usage
tag="$1"
shift
sed "/<<Release>>=/ {
 n;
 c\
$tag
q}" $*
--8<-------------------------------------------------------->8---
 
I still see the whole file:
 
--8<-------------------------------------------------------->8---
%sh make-release release1 sample.txt
Lorem ipsum dolor...
 
<<Release>>=
release1
@
 
... sit a met [...]
%
--8<-------------------------------------------------------->8---
 
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.
 
I've been reading Dale Dougherty and Arnold Robin's ``sed & awk'' book.
If you have any recommended sed-related bibliography, I'd appreciate it,
too.
 


Date Sujet#  Auteur
18 Dec20:46 * a sed question48Salvador Mirzo
18 Dec21:12 +- Re: a sed question1John-Paul Stewart
19 Dec02:14 +* Re: a sed question16Ralf Damaschke
19 Dec13:05 i`* Re: a sed question15Salvador Mirzo
20 Dec01:55 i `* Re: a sed question14Ralf Damaschke
20 Dec13:44 i  `* Re: a sed question13Kenny McCormack
21 Dec01:17 i   `* Re: a sed question12Ralf Damaschke
21 Dec04:09 i    `* Re: a sed question11Kaz Kylheku
21 Dec04:36 i     +* sed... (Was: a sed question)8Kenny McCormack
21 Dec04:57 i     i`* Re: sed... (Was: a sed question)7Kaz Kylheku
21 Dec15:38 i     i +* Re: sed... (Was: a sed question)4Janis Papanagnou
21 Dec17:29 i     i i`* Re: sed... (Was: a sed question)3Janis Papanagnou
21 Dec23:23 i     i i `* Re: sed...2Keith Thompson
22 Dec00:33 i     i i  `- Re: sed...1Janis Papanagnou
21 Dec22:46 i     i `* Re: sed... (Was: a sed question)2Lars Poulsen
22 Dec22:22 i     i  `- Re: sed... (Was: a sed question)1Kaz Kylheku
21 Dec15:35 i     +- Re: a sed question1Janis Papanagnou
22 Dec01:43 i     `- Re: a sed question1Ralf Damaschke
20 Dec15:55 +* Re: a sed question18Janis Papanagnou
20 Dec16:11 i+* Checking for right # of args in a shell script (Was: a sed question)3Kenny McCormack
20 Dec16:49 ii`* Re: Checking for right # of args in a shell script (Was: a sed question)2Janis Papanagnou
20 Dec18:43 ii `- Re: Checking for right # of args in a shell script (Was: a sed question)1Kenny McCormack
21 Dec13:17 i+* Re: a sed question13Salvador Mirzo
21 Dec16:19 ii+* Re: a sed question7Janis Papanagnou
21 Dec22:41 iii`* Re: a sed question6Keith Thompson
22 Dec00:50 iii `* Re: a sed question5Janis Papanagnou
22 Dec01:26 iii  +* Re: a sed question2Keith Thompson
22 Dec01:41 iii  i`- Re: a sed question1Janis Papanagnou
22 Dec01:31 iii  `* Re: a sed question2Lawrence D'Oliveiro
22 Dec02:06 iii   `- Re: a sed question1Janis Papanagnou
21 Dec16:34 ii+* Re: a sed question4Andy Walker
21 Dec17:14 iii+- Re: a sed question1Janis Papanagnou
21 Dec19:21 iii`* Re: a sed question2Salvador Mirzo
21 Dec20:48 iii `- Re: a sed question1Janis Papanagnou
21 Dec19:20 ii`- Re: a sed question1Helmut Waitzmann
22 Dec19:23 i`- Re: a sed question1Janis Papanagnou
21 Dec15:13 `* Re: a sed question12Ed Morton
21 Dec22:09  `* Re: a sed question11Lawrence D'Oliveiro
22 Dec01:02   +* Re: a sed question8Janis Papanagnou
22 Dec01:28   i`* Re: a sed question7Lawrence D'Oliveiro
22 Dec01:36   i +* Re: a sed question5Keith Thompson
22 Dec02:52   i i`* Re: a sed question4Lawrence D'Oliveiro
22 Dec06:09   i i `* Re: a sed question3Keith Thompson
22 Dec06:56   i i  `* Re: a sed question2Lawrence D'Oliveiro
22 Dec07:55   i i   `- Re: a sed question1Keith Thompson
22 Dec02:22   i `- Re: a sed question1Janis Papanagnou
22 Dec02:09   +- Re: a sed question1Kenny McCormack
22 Dec21:03   `- Re: a sed question1Kaz Kylheku

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