Shell Scripts: Difference between revisions

← Older edit Newer edit →

VisualWikitext

@@ Line 23: / Line 23: @@
 # default.nix
 {
-   outputTxtPath = stdenv.mkDerivation rec {
+   outputTxtDrv = stdenv.mkDerivation rec {
      name = "output.txt";
      # disable unpackPhase etc
@@ Line 55: / Line 55: @@
 # default.nix
 {
-   outputTxtPath = runCommand "output.txt" {
+   outputTxtDrv = runCommand "output.txt" {
      nativeBuildInputs = [ coreutils jq ];
      # only strings can be passed to builder
@@ Line 111: / Line 111: @@
 $ 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>