Shell parameter expansion in nix configuration file

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1

Hi there !
I want to add a function to be available in my shell:

iain_nr() {
      output="${1%%.*}_iain_nr.${1##*.}"
      echo $output
      gmic -input $1 iain_nr_2019 1,0,0,0,0.5,1,0,30,3,0,5,2,0.5,4,0 -output "${output}"
    }

So I add this to environment.shellInit as such:

environment.shellInit = ''
     iain_nr() {
       output="${1%%.*}_iain_nr.${1##*.}"
       echo $output
       gmic -input $1 iain_nr_2019 1,0,0,0,0.5,1,0,30,3,0,5,2,0.5,4,0 -output "${output}"
     }
  '';

But I get this error:

error: syntax error, unexpected invalid token, expecting '}'

       at /etc/nixos/aliases.nix:29:18:

           28|     iain_nr() {
           29|       output="${1%%.*}_iain_nr.${1##*.}"
             |                  ^
           30|       echo $output
(use '--show-trace' to show detailed location information)

What is the correct way to use shell parameter expansion in a nix string?

2

Use two single quotes to escape a dollar sign in multi-line strings, see Data Types - Nix Reference Manual

2 Likes
3

Perfect, it worked as expected. Thank you.

environment.shellInit = ''
    iain_nr() {
      output="''${1%%.*}_iain_nr.''${1##*.}"
      echo $output
      gmic -input $1 iain_nr_2019 1,0,0,0,0.5,1,0,30,3,0,5,2,0.5,4,0 -output "''${output}"
    }
  '';
1 Like