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Shell scripts: Difference between revisions

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the package <code>writeShellScript</code> can be used to add shell scripts to nix expressions
The package <code>writeShellScript</code> can be used to add shell scripts to nix expressions


<syntaxHighlight lang="nix">
<syntaxHighlight lang="nix">
  someBuildHelper = { name, sha256 }:
someBuildHelper = { name, sha256 }:
    stdenv.mkDerivation {
  stdenv.mkDerivation {
      inherit name;
    inherit name;
      outputHashMode = "recursive";
    outputHashMode = "recursive";
      outputHashAlgo = "sha256";
    outputHashAlgo = "sha256";
      outputHash = sha256;
    outputHash = sha256;
      builder = writeShellScript "builder.sh" ''
    builder = writeShellScript "builder.sh" ''
        echo "hi, my name is ''${0}" # escape bash variable
      echo "hi, my name is ''${0}" # escape bash variable
        echo "hi, my hash is ${sha256}" # use nix variable
      echo "hi, my hash is ${sha256}" # use nix variable
        echo "hello world" >output.txt
      echo "hello world" >output.txt
      '';
    '';
    };
  };
</syntaxHighlight>
</syntaxHighlight>


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Longer bash scripts are usually stored as external script files, and called from Nix:
Longer bash scripts are usually stored as external script files, and called from Nix:


<syntaxHighlight lang="nix">
{{file|default.nix|nix|3=
# default.nix
{
{
   outputTxtPath = stdenv.mkDerivation rec {
   outputTxtDrv = stdenv.mkDerivation rec {
     name = "output.txt";
     name = "output.txt";
     # disable unpackPhase etc
     # disable unpackPhase etc
Line 36: Line 35:
   };
   };
}
}
</syntaxHighlight>
}}


<syntaxHighlight lang="bash">
{{file|builder.sh|sh|3=
# builder.sh
echo "$someString $(echo "$someJson" | jq -r '.dst') $someNumber" >$out
echo "$someString $(echo "$someJson" | jq -r '.dst') $someNumber" >$out
</syntaxHighlight>
}}


See also
See also
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Instead of <code>stdenv.mkDerivation</code>, we can also use <code>runCommand</code> to call an external bash script:
Instead of <code>stdenv.mkDerivation</code>, we can also use <code>runCommand</code> to call an external bash script:


<syntaxHighlight lang="nix">
{{file|default.nix|nix|3=
# default.nix
{
{
   outputTxtPath = runCommand "output.txt" {
   outputTxtDrv = runCommand "output.txt" {
     nativeBuildInputs = [ coreutils jq ];
     nativeBuildInputs = [ coreutils jq ];
     # only strings can be passed to builder
     # only strings can be passed to builder
Line 63: Line 60:
   } (builtins.readFile ./builder.sh);
   } (builtins.readFile ./builder.sh);
}
}
</syntaxHighlight>
}}


== Packaging ==
== Packaging ==


example:
Example:


<syntaxHighlight lang="nix">
<syntaxHighlight lang="nix">
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         --prefix PATH : ${lib.makeBinPath [ bash subversion ]}
         --prefix PATH : ${lib.makeBinPath [ bash subversion ]}
     '';
     '';
   };
   }
</syntaxHighlight>
</syntaxHighlight>


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=== Command not found ===
=== Command not found ===


for example, the script throws the error <code>svn: command not found</code>, because the dependency <code>subversion</code> is missing.
For example, the script throws the error <code>svn: command not found</code>, because the dependency <code>subversion</code> is missing.


when a command is missing, you can use <code>nix-locate</code> to find the package name. for example, the <code>stat</code> command:
When a command is missing, you can use <code>nix-locate</code> to find the package name. for example, the <code>stat</code> command:


<syntaxHighlight lang="console">
<syntaxHighlight lang="console">
$ nix-locate bin/stat | grep 'bin/stat$'
$ nix-locate bin/stat | grep 'bin/stat$'
coreutils.out                                         0 s /nix/store/vr96j3cxj75xsczl8pzrgsv1k57hcxyp-coreutils-8.31/bin/stat
coreutils.out       0 s /nix/store/vr96j3cxj75xsczl8pzrgsv1k57hcxyp-coreutils-8.31/bin/stat
</syntaxHighlight>
 
== Debugging embedded scripts ==
 
When a bash script fails, it prints only an error message, but no code location.
 
To trace commands and line numbers, we can use
 
{{file|test-trace.nix|nix|3=
{ runCommand, coreutils }:
runCommand "output.txt" { nativeBuildInputs = [ coreutils ]; } ''
  # line 5 in nix file = line 1 in bash script -> offset 4
  PS4='+ Line $(expr $LINENO + 4): '
  set -o xtrace # print commands
 
  echo hello >$out # line 9 in nix file
 
  set +o xtrace # hide commands
''
 
}}
 
<syntaxHighlight lang="console">
$ nix-build -E 'with import <nixpkgs> { }; callPackage ./test-trace.nix { }'
this derivation will be built:
  /nix/store/2v5biwny8plpyk2bv6cfr41ppp0a1i4k-output.txt.drv
building '/nix/store/2v5biwny8plpyk2bv6cfr41ppp0a1i4k-output.txt.drv'...
++ Line 9: echo hello
++ Line 11: set +o xtrace
/nix/store/ppidmnpd5m762x9kqj8jd3g7df7dknrz-output.txt
</syntaxHighlight>
</syntaxHighlight>


== Posix Shell ==
== Posix Shell ==


some environments (like OpenWRT, via <code>busybox</code>) offer only a "limited" shell (<code>sh</code> instead of <code>bash</code>).
Some environments (like OpenWRT, via <code>busybox</code>) offer only a "limited" shell (<code>sh</code> instead of <code>bash</code>).


on nixos, posix shells are provided by the packages <code>dash</code> and <code>posh</code>
On NixOS, posix shells are provided by the packages <code>dash</code> and <code>posh</code>.


== See also ==
== See also ==


* [[Nix-shell shebang]]
* [https://nixos.org/manual/nixpkgs/stable/#ssec-stdenv-functions Shell functions section in the Nixpkgs manual]
* [https://nixos.org/manual/nixpkgs/stable/#ssec-stdenv-functions Shell functions section in the Nixpkgs manual]
* [https://gist.github.com/travisbhartwell/f972aab227306edfcfea nix-shell and Shebang Lines]
* [https://ertt.ca/nix/shell-scripts/ Shell Scripts with Nix]
[[Category:Development]]
[[Category:Shell]]
Retrieved from "https://wiki.nixos.org/wiki/Shell_scripts"