Execline: Difference between revisions

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 </syntaxHighlight>
+== Blocks ==
+Some execline programs take code blocks as their arguments. Blocks are delimited by <code>{}</code> in execlineb scripts. In the following example the <code>pipeline</code> program executes a block of commands in the background with a pipe connecting the stdin of that block to the stdout of the command-line following the block.
+<syntaxHighlight lang="nix">
+{ pkgs ? import <nixpkgs> { } }:
+pkgs.execline.passthru.writeScript "wrap-cowsay" "-s0" ''
+  pipeline -w { ${pkgs.lib.getExe pkgs.cowsay} }
+  $@
+''
+</syntaxHighlight>
+=== Block quoting ===
+execlineb parses <code>{}</code> blocks and constructs a command-line where each block item is prepended with a whitespace (\x20) and terminated with an empty string. This quoting can be done in pure Nix.
+Given the function <code>quoteExecline</code> as
+<syntaxHighlight lang="nix">
+builtins.foldl' (acc: arg: acc ++ (
+  if builtins.isList arg
+    then map (_: " ${_}") (quoteExecline arg) ++ [ "" ]
+    else [ arg ]
+  )) [ ];
+</syntaxHighlight>
+then the expression
+<syntaxHighlight lang="nix">
+args: lib.escapeShellArgs (quoteExecline [ "pipeline" "-w" [ (lib.getExe pkgs.cowsay) ] ] ++ args)
+</syntaxHighlight>
+would produce the command-line executed by <code>execlineb</code> in the previous "wrap-cowsay" example when given the same arguments.
 [[Category:Cookbook]]