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Shell Scripts: Difference between revisions
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imported>Milahu (+ demo for writeShellScript) |
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<syntaxHighlight lang="nix"> | <syntaxHighlight lang="nix"> | ||
someBuildHelper = { name, sha256 }: | someBuildHelper = { name, sha256 }: | ||
stdenv.mkDerivation { | stdenv.mkDerivation { | ||
| Line 16: | Line 15: | ||
}; | }; | ||
</syntaxHighlight> | </syntaxHighlight> | ||
== External builder.sh script == | |||
Longer bash scripts are usually stored as external script files, and called from Nix: | |||
<syntaxHighlight lang="nix"> | |||
# default.nix | |||
{ | |||
outputTxtDrv = stdenv.mkDerivation rec { | |||
name = "output.txt"; | |||
# disable unpackPhase etc | |||
phases = "buildPhase"; | |||
builder = ./builder.sh; | |||
nativeBuildInputs = [ coreutils jq ]; | |||
PATH = lib.makeBinPath nativeBuildInputs; | |||
# only strings can be passed to builder | |||
someString = "hello"; | |||
someNumber = builtins.toString 42; | |||
someJson = builtins.toJSON { dst = "world"; }; | |||
}; | |||
} | |||
</syntaxHighlight> | |||
<syntaxHighlight lang="bash"> | |||
# builder.sh | |||
echo "$someString $(echo "$someJson" | jq -r '.dst') $someNumber" >$out | |||
</syntaxHighlight> | |||
See also | |||
* [https://github.com/NixOS/nixpkgs/issues/23099 make a derivation with no source] | |||
* [https://nixos.org/guides/nix-pills/working-derivation.html Nix Pills: Chapter 7. Working Derivation] | |||
=== runCommand + builder.sh === | |||
Instead of <code>stdenv.mkDerivation</code>, we can also use <code>runCommand</code> to call an external bash script: | |||
<syntaxHighlight lang="nix"> | |||
# default.nix | |||
{ | |||
outputTxtDrv = runCommand "output.txt" { | |||
nativeBuildInputs = [ coreutils jq ]; | |||
# only strings can be passed to builder | |||
someString = "hello"; | |||
someNumber = builtins.toString 42; | |||
someJson = builtins.toJSON { dst = "world"; }; | |||
} (builtins.readFile ./builder.sh); | |||
} | |||
</syntaxHighlight> | |||
== Packaging == | |||
example: | |||
<syntaxHighlight lang="nix"> | |||
# nix-build -E 'with import <nixpkgs> { }; callPackage ./default.nix { }' | |||
{ stdenv | |||
, lib | |||
, fetchFromGitHub | |||
, bash | |||
, subversion | |||
, makeWrapper | |||
}: | |||
stdenv.mkDerivation { | |||
pname = "github-downloader"; | |||
version = "08049f6"; | |||
src = fetchFromGitHub { | |||
# https://github.com/Decad/github-downloader | |||
owner = "Decad"; | |||
repo = "github-downloader"; | |||
rev = "08049f6183e559a9a97b1d144c070a36118cca97"; | |||
sha256 = "073jkky5svrb7hmbx3ycgzpb37hdap7nd9i0id5b5yxlcnf7930r"; | |||
}; | |||
buildInputs = [ bash subversion ]; | |||
nativeBuildInputs = [ makeWrapper ]; | |||
installPhase = '' | |||
mkdir -p $out/bin | |||
cp github-downloader.sh $out/bin/github-downloader.sh | |||
wrapProgram $out/bin/github-downloader.sh \ | |||
--prefix PATH : ${lib.makeBinPath [ bash subversion ]} | |||
''; | |||
} | |||
</syntaxHighlight> | |||
<code>wrapProgram</code> will move the original script to <code>.github-downloader.sh-wrapped</code> | |||
=== Command not found === | |||
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: | |||
<syntaxHighlight lang="console"> | |||
$ nix-locate bin/stat | grep '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 | |||
<syntaxHighlight lang="nix"> | |||
# test-trace.nix | |||
{ 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> | |||
<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> | |||
== Posix Shell == | |||
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> | |||
== See also == | |||
* [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] | |||