Re: grep: add option for better usability in pipelines
On Thu, Feb 17, 2022 at 3:27 PM Ulrich Eckhardt
wrote:
> >
> > Why do we need to implement a workaround in grep while you can
> > do this in shell to ignore the exit code of grep?
> >
> > { grep issue
> `grep -p ...` rather replaces `grep ... || test $? = 1`. The advantage
> is that it is explicit about what it does. Understanding the intent of
> `-p` or `--pipe` is easier than understanding the alternative.
>
Unless you can propose the '-p' option to POSIX will busybox implement it as
you say.
The problem here is portability. FreeBSD grep
(https://www.freebsd.org/cgi/man.cgi?query=grep) has a different meaning with
'-p' so it won't be portable to use '-p' in shell scripts. And the long option
'--pipe' isn't quite helpful either as it would end up being a GNU-only
extension and so is discouraged to use in shell scripts (which defeats the
purpose of your '--pipe' option in the first place).
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Re: grep: add option for better usability in pipelines
On Thu, Feb 17, 2022 at 12:50 PM Michael Conrad wrote:
>
> On 2/16/22 19:32, Kang-Che Sung wrote:
> >
> >> Now, for an example where it makes a difference. Consider a Bash script
> >> like this:
> >>
> >># enable automatic error handling
> >>set -eo pipefail
> >># check for string "issues" in a logfile
> >>cat logfile | grep issue | sort --unique
> >>
> >> If there are no issues in the logs, grep return exit code 1 and the
> >> shell interprets this as an error and exits itself.
> >>
> > Why do we need to implement a workaround in grep while you can
> > do this in shell to ignore the exit code of grep?
> >
> > { grep issue
> In order to implement his suggestion, you need to only ignore exit code
> 1, while still allowing other exit codes to abort the script. (like a
> system error while reading the file)
{ grep issue But also, I've never seen ":" used as a command... where is that
> documented? Is it equivalent to 'true'?
https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.71/html_node/Limitations-of-Builtins.html
Look for the "true" section.
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Re: grep: add option for better usability in pipelines
On Thu, 17 Feb 2022 08:32:06 +0800
Kang-Che Sung wrote:
> On Thu, Feb 17, 2022 at 8:01 AM Ulrich Eckhardt
> wrote:
> > Now, for an example where it makes a difference. Consider a Bash
> > script like this:
> >
> > # enable automatic error handling
> > set -eo pipefail
> > # check for string "issues" in a logfile
> > cat logfile | grep issue | sort --unique
> >
> > If there are no issues in the logs, grep return exit code 1 and the
> > shell interprets this as an error and exits itself.
> >
>
> Why do we need to implement a workaround in grep while you can
> do this in shell to ignore the exit code of grep?
>
> { grep issue > I've implemented that feature here, though it lacks tests yet:
> > https://github.com/UlrichEckhardt/busybox/tree/grep-pipe-option
> > Also, I'm currently trying to get the same feature into GNU grep as
> > well, the long form `--pipe` is used there. I've also considered
> > `--filter` (because it only filters) as alternative. I'm not fully
> > happy with either one, maybe someone here comes up with a better
> > suggestion.
>
> I don't see the '--pipe' option in GNU grep manual
>
Misunderstanding: It's not in there! I have it implemented already and
I'm trying to get it incorporated there, which takes time due to FSF
paperwork.
Cheers!
Uli
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Re: grep: add option for better usability in pipelines
On 2/16/22 19:32, Kang-Che Sung wrote:
Now, for an example where it makes a difference. Consider a Bash script
like this:
# enable automatic error handling
set -eo pipefail
# check for string "issues" in a logfile
cat logfile | grep issue | sort --unique
If there are no issues in the logs, grep return exit code 1 and the
shell interprets this as an error and exits itself.
Why do we need to implement a workaround in grep while you can
do this in shell to ignore the exit code of grep?
{ grep issue
In order to implement his suggestion, you need to only ignore exit code
1, while still allowing other exit codes to abort the script. (like a
system error while reading the file)
But also, I've never seen ":" used as a command... where is that
documented? Is it equivalent to 'true'?
-Mike C
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Re: grep: add option for better usability in pipelines
On Thu, Feb 17, 2022 at 8:01 AM Ulrich Eckhardt
wrote:
>
> I've implemented a `-p` flag for grep, which disables a behaviour that
> the exit status is used (abused?) to signal whether any match
> occurred.
The behaviour is POSIX.
> Now, for an example where it makes a difference. Consider a Bash script
> like this:
>
> # enable automatic error handling
> set -eo pipefail
> # check for string "issues" in a logfile
> cat logfile | grep issue | sort --unique
>
> If there are no issues in the logs, grep return exit code 1 and the
> shell interprets this as an error and exits itself.
>
Why do we need to implement a workaround in grep while you can
do this in shell to ignore the exit code of grep?
{ grep issue I've implemented that feature here, though it lacks tests yet:
> https://github.com/UlrichEckhardt/busybox/tree/grep-pipe-option
> Also, I'm currently trying to get the same feature into GNU grep as
> well, the long form `--pipe` is used there. I've also considered
> `--filter` (because it only filters) as alternative. I'm not fully
> happy with either one, maybe someone here comes up with a better
> suggestion.
I don't see the '--pipe' option in GNU grep manual
and I don't think it would be needed considering that you can tell the
shell to ignore an exit code already.
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grep: add option for better usability in pipelines
Greetings! I've implemented a `-p` flag for grep, which disables a behaviour that the exit status is used (abused?) to signal whether any match occurred. In many cases, you won't notice this. Also, in many cases, shell scripts don't check for errors. Now, for an example where it makes a difference. Consider a Bash script like this: # enable automatic error handling set -eo pipefail # check for string "issues" in a logfile cat logfile | grep issue | sort --unique If there are no issues in the logs, grep return exit code 1 and the shell interprets this as an error and exits itself. I've implemented that feature here, though it lacks tests yet: https://github.com/UlrichEckhardt/busybox/tree/grep-pipe-option Also, I'm currently trying to get the same feature into GNU grep as well, the long form `--pipe` is used there. I've also considered `--filter` (because it only filters) as alternative. I'm not fully happy with either one, maybe someone here comes up with a better suggestion. If you want, grab the first commit in there, it just fixes a small typo. I'd be happy to hear any suggestions! Cheers! Uli ___ busybox mailing list busybox@busybox.net http://lists.busybox.net/mailman/listinfo/busybox
