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diff --git a/nix/runExecline/runExecline.nix b/nix/runExecline/runExecline.nix
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+++ b/nix/runExecline/runExecline.nix
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+{ pkgs, stdenv, lib, getBins, escapeExecline }:
+
+# runExecline is a primitive building block
+# for writing non-kitchen sink builders.
+#
+# It’s conceptually similar to `runCommand`,
+# but instead of concatenating bash scripts left
+# and right, it actually *uses* the features of
+# `derivation`, passing things to `args`
+# and making it possible to overwrite the `builder`
+# in a sensible manner.
+#
+# Additionally, it provides a way to pass a nix string
+# to `stdin` of the build script.
+#
+# Similar to //nix/writeExecline, the passed script is
+# not a string, but a nested list of nix lists
+# representing execline blocks. Escaping is
+# done by the implementation, the user can just use
+# normal nix strings.
+#
+# Example:
+#
+#  runExecline "my-drv" { stdin = "hi!"; } [
+#    "importas" "out" "out"
+#    # this pipes stdout of s6-cat to $out
+#    # and s6-cat redirects from stdin to stdout
+#    "redirfd" "-w" "1" "$out" bins.s6-cat
+#  ]
+#
+# which creates a derivation with "hi!" in $out.
+#
+# See ./tests.nix for more examples.
+
+
+let
+  bins = getBins pkgs.execline [
+    "execlineb"
+    { use = "if"; as = "execlineIf"; }
+    "redirfd"
+    "importas"
+    "exec"
+  ]
+  // getBins pkgs.s6-portable-utils [
+    "s6-cat"
+    "s6-grep"
+    "s6-touch"
+    "s6-test"
+    "s6-chmod"
+  ];
+
+in
+
+# TODO: move name into the attrset
+name:
+{
+  # a string to pass as stdin to the execline script
+  stdin ? ""
+  # a program wrapping the acutal execline invocation;
+  # should be in Bernstein-chaining style
+, builderWrapper ? bins.exec
+  # additional arguments to pass to the derivation
+, derivationArgs ? { }
+}:
+# the execline script as a nested list of string,
+# representing the blocks;
+# see docs of `escapeExecline`.
+execline:
+
+# those arguments can’t be overwritten
+assert !derivationArgs ? system;
+assert !derivationArgs ? name;
+assert !derivationArgs ? builder;
+assert !derivationArgs ? args;
+
+derivation (derivationArgs // {
+  # TODO(Profpatsch): what about cross?
+  inherit (stdenv) system;
+  inherit name;
+
+  # okay, `builtins.toFile` does not accept strings
+  # that reference drv outputs. This means we need
+  # to pass the script and stdin as envvar;
+  # this might clash with another passed envar,
+  # so we give it a long & unique name
+  _runExeclineScript =
+    let
+    in escapeExecline execline;
+  _runExeclineStdin = stdin;
+  passAsFile = [
+    "_runExeclineScript"
+    "_runExeclineStdin"
+  ] ++ derivationArgs.passAsFile or [ ];
+
+  # the default, exec acts as identity executable
+  builder = builderWrapper;
+
+  args = [
+    bins.importas # import script file as $script
+    "-ui" # drop the envvar afterwards
+    "script" # substitution name
+    "_runExeclineScriptPath" # passed script file
+
+    bins.importas # do the same for $stdin
+    "-ui"
+    "stdin"
+    "_runExeclineStdinPath"
+
+    bins.redirfd # now we
+    "-r" # read the file
+    "0" # into the stdin of execlineb
+    "$stdin" # that was given via stdin
+
+    bins.execlineb # the actual invocation
+    # TODO(Profpatsch): depending on the use-case, -S0 might not be enough
+    # in all use-cases, then a wrapper for execlineb arguments
+    # should be added (-P, -S, -s).
+    "-S0" # set $@ inside the execline script
+    "-W" # die on syntax error
+    "$script" # substituted by importas
+  ];
+})