# How to access current selection by reference in shell?

**URL:** <https://discuss.kakoune.com/t/how-to-access-current-selection-by-reference-in-shell/2602>\
**Category:** Help\
**Created:** [December 13, 2024, 10:41pm UTC](https://discuss.kakoune.com/t/how-to-access-current-selection-by-reference-in-shell/2602 "2024-12-13T22:41:18Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![gregk](https://discuss.kakoune.com/letter_avatar_proxy/v4/letter/g/958977/32.png) [@gregk](https://discuss.kakoune.com/u/gregk)\
**Post date:** [December 13, 2024, 10:41pm UTC](https://discuss.kakoune.com/t/how-to-access-current-selection-by-reference-in-shell/2602/1 "2024-12-13T22:41:18Z")

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I’m editing a document with paragraph numbers and cross references. I’ve written an awk script to maintain the numbers and references as paragraphs are added or deleted. As far as I can tell this requires reading the document once to establish the index and a second time to update the indices.

The bash shell will only pass stdin to awk ONCE. In the shell the solution is awk filename filename, i.e. pass the filename (reference) twice to awk.

Under Kakoune the pipe commands will also pass the current selection to the script by reference only ONCE. I can’t find the syntax to pass the current selection to the script explicitly by reference to allow me to do it twice. $kak\_reg\_dot expands to the VALUE of the selection, not a REFERENCE. e.g.  
:echo %sh{echo $kak\_reg\_dot}  
works. My standard shell solution to pass by reference  
:echo %sh{cat \<(echo $kak\_reg\_dot)}  
leads Kakoune to seem to object to \<(echo $kak\_reg\_dot)  
Am I missing something basic?

There are workarounds like

- passing variables to awk by value
- saving the buffer and passing the filename twice to awk as in the shell
- splitting the script into two pipe steps and passing the index between the 2 scripts in a temp file or named pipe

This is mostly to help me and others understand the fine points of the Kakoune design for communication with the shell.

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**Author:** ![krobelus](https://discuss.kakoune.com/user_avatar/discuss.kakoune.com/krobelus/32/616_2.png) [@krobelus](https://discuss.kakoune.com/u/krobelus)\
**Post date:** [December 14, 2024, 3:12am UTC](https://discuss.kakoune.com/t/how-to-access-current-selection-by-reference-in-shell/2602/2 "2024-12-14T03:12:34Z")

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you can use the value multiple times

```auto
nop %sh{
  printf %s "$kak_selection" | foo
  printf %s "$kak_selection" | bar
}

```

> %sh{cat \<(echo $kak\_reg\_dot)}

process substitutions are not (yet?) POSIX so this may depend on which shell you’re using

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**Author:** ![gregk](https://discuss.kakoune.com/letter_avatar_proxy/v4/letter/g/958977/32.png) [@gregk](https://discuss.kakoune.com/u/gregk)\
**Post date:** [December 14, 2024, 6:32am UTC](https://discuss.kakoune.com/t/how-to-access-current-selection-by-reference-in-shell/2602/3 "2024-12-14T06:32:51Z")

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Great catch!  
According to ps -p $$, bash is running at the terminal command prompt  
However :echo %sh{ps -p $$} shows sh running under Kakoune.  
man sh indicates it is dash and the process substitution error also occurs at a dash prompt outside kakoune.

:echo %sh{echo “cat \<(echo hello)”|bash}  
successfully returns hello which is a workaround

Unlinking /bin/sh and /usr/bin/sh results in Kakoune refusing to start because it can’t find a Posix compliant shell. Kakoune did start with /bin/sh and /usr/bin/sh symlinked to bash and process substitution ran successfully under Kakoune, but I assume that is unsupported. I understand that it might be difficult to support the multitude of \*nix shells. If I were better at C++ I would try running bash to find out what breaks…

I will split the script into two Posix compliant steps. The first step will rewrite stdin to the second step as well as writing the change indexes to a named pipe for step 2 to also process. This also has the benefit of playing nice with the Kakoune pipe commands.

Now I know to test Kakoune scripts under dash. thanks

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**Author:** ![Screwtapello](https://discuss.kakoune.com/user_avatar/discuss.kakoune.com/screwtapello/32/12_2.png) [@Screwtapello](https://discuss.kakoune.com/u/Screwtapello)\
**Post date:** [December 14, 2024, 6:44am UTC](https://discuss.kakoune.com/t/how-to-access-current-selection-by-reference-in-shell/2602/4 "2024-12-14T06:44:53Z")

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> [@gregk](#):
>
> Kakoune did start with /bin/sh and /usr/bin/sh symlinked to bash and process substitution ran successfully under Kakoune, but I assume that is unsupported.

When bash is started as `sh` (such as via a symlink) it tries to start up in a POSIX-compatible mode, and many Linux distributions _do_ use bash as `/bin/sh`, so it’s supported by bash and probably by other tools too.

However, if your `/bin/sh` defaults to dash, you’re probably on a Debian-derived distribution, and tinkering with `/bin/sh` is not supported by Debian.

Kakoune will use the `$KAKOUNE_POSIX_SHELL` environment variable to locate a POSIX shell, if it’s set, so you can try Kakoune with different shells without having to mess with system-managed parts of the filesystem.

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<div class="post-metadata">

**Author:** ![gregk](https://discuss.kakoune.com/letter_avatar_proxy/v4/letter/g/958977/32.png) [@gregk](https://discuss.kakoune.com/u/gregk)\
**Post date:** [December 14, 2024, 7:08am UTC](https://discuss.kakoune.com/t/how-to-access-current-selection-by-reference-in-shell/2602/5 "2024-12-14T07:08:16Z")

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> [@Screwtapello](#):
>
> However, if your `/bin/sh` defaults to dash, you’re probably on a Debian-derived distribution, and tinkering with `/bin/sh` is not supported by Debian.

Yes, Debian 12 Bookworm. I see the warnings on Reddit etc about tampering with /bin/sh Thanks for the heads up.