nix-bundle.sh: Modernize CLI

TODOs:

* [ ] Update `README.md`
* [ ] What about `nix2appimage.sh`?

nix-bundle.sh

@@ -1,56 +1,165 @@
 #!/usr/bin/env sh
 
-if [ "$#" -lt 2 ]; then
-    cat <<EOF
+fail() {
+    echo "Try '$0 --help'." >&2
+    exit 2
+}
 
-Usage: $0 TARGET EXECUTABLE
+build() {
+    linkdir=$(mktemp -d)
+    nix build "$@" --out-link "$linkdir/result"
+    readlink "$linkdir/result"
+}
 
-Create a single-file bundle from the nixpkgs attribute "TARGET".
-EXECUTABLE should be relative to the TARGET's output path.
-
-For example:
-
-$ $0 hello /bin/hello
-$ ./hello
-Hello, world!
-
-EOF
-
-    exit 1
-fi
+check_arg() {
+    if [ $# -le 1 ]
+    then
+        echo "error: flag '$1' requires an argument" >&2
+        fail
+    fi
+}
 
 nix_file=`dirname $0`/default.nix
 
-target="$1"
-shift
+# Read arguments
 
-extraTargets=
-if [ "$#" -gt 1 ]; then
-    while [ "$#" -gt 1 ]; do
-        extraTargets="$extraTargets $1"
-        shift
-    done
+build_flags=()
+unset bin
+targets=()
+
+while [ $# -ne 0 ]
+do
+    case "$1" in
+        -f|--file|-I|--include)
+            check_arg "$@"
+            build_flags+=("$1")
+            shift
+            build_flags+=("$1")
+            shift
+            ;;
+        --arg|--argstr)
+            if [ $# -le 2 ]
+            then
+                echo "error: flag '$1' requires two arguments" >&2
+                fail
+            fi
+            build_flags+=("$1")
+            shift
+            build_flags+=("$1")
+            shift
+            build_flags+=("$1")
+            shift
+            ;;
+        --bin)
+            check_arg "$@"
+            shift
+            bin="$1"
+            shift
+            ;;
+        -h|--help)
+            cat <<EOF >&2
+Usage: $0 <FLAGS>... [<TARGET>] <targets>...
+
+Summary: Similar to nix build, but creates a single-file bundle.
+
+Flags:
+      --arg <NAME> <EXPR>       argument to be passed to Nix functions
+      --argstr <NAME> <STRING>  string-valued argument to be passed to Nix functions
+  -f, --file <FILE>             evaluate FILE rather than the default
+  -I, --include <PATH>          add a path to the list of locations used to look up <...> file names
+      --bin <BINARY>            the binary to bundle, relative to TARGET's output path
+
+Examples:
+
+  To bundle GNU Hello from NixOS 19.03:
+  $ $0 -f channel:nixos-19.03 hello --bin /bin/hello
+
+  To bundle the executable from within a project that has a default.nix for build:
+  $ $0 --bin /bin/name-of-the-executable
+EOF
+            exit 0
+            ;;
+        --)
+            shift
+            break
+            ;;
+        -*)
+            echo "error: unrecognized flag '$1'" >&2
+            fail
+            ;;
+        *)
+            targets+=("$1")
+            shift
+            ;;
+    esac
+done
+
+while [ $# -ne 0 ]
+do
+    targets+=("$1")
+    shift
+done
+
+# Check if all required arguments were passed
+
+if [ -z ${bin+x} ]
+then
+    echo "error: flag '--bin' is required" >&2
+    fail
 fi
 
-exec="$1"
-shift
+# Create tmp directory for the links produced by `nix build`
+
+linkdir=$(mktemp -d)
+build_flags+=("--out-link")
+build_flags+=("$linkdir/result")
+
+# Build targets
+
+target_path=
+extra_target_paths=
+
+for target in "${targets[@]}"
+do
+    nix build "${build_flags[@]}" "$target" || exit $?
+    if [ -z "$target_path" ]
+    then
+        target_path="$(readlink "$linkdir/result")"
+    else
+        extra_target_paths="$extra_target_paths $(readlink "$linkdir/result")"
+    fi
+done
+
+if [ -z "$target_path" ]
+then
+    nix build "${build_flags[@]}" || exit $?
+    target_path="$(readlink "$linkdir/result")"
+fi
+
+# Determine bootstrap function -- This seems like a total hack!
 
 bootstrap=nix-bootstrap
-if [ "$target" = "nix-bundle" ] || [ "$target" = "nixStable" ] || [ "$target" = "nixUnstable" ] || [ "$target" = "nix" ]; then
+if [ "${targets[0]}" = "nix-bundle" ] || [ "${targets[0]}" = "nixStable" ] || [ "${targets[0]}" = "nixUnstable" ] || [ "${targets[0]}" = "nix" ]; then
     bootstrap=nix-bootstrap-nix
-elif ! [ -z "$extraTargets" ]; then
+elif ! [ -z "$extra_target_paths" ]; then
     bootstrap=nix-bootstrap-path
 fi
 
-expr="with import <nixpkgs> {}; with import $nix_file {}; $bootstrap { target = $target; extraTargets = [ $extraTargets ]; run = \"$exec\"; }"
+# Run bootstrap function
+
+expr="(with import $nix_file {}; $bootstrap { target = $target_path; extraTargets = [$extra_target_paths ]; run = \"$bin\"; })"
+
+echo $expr
 
 out=$(nix-store --no-gc-warning -r $(nix-instantiate --no-gc-warning -E "$expr"))
 
+# Copy the created bundle to the working directory
+
 if [ -z "$out" ]; then
   >&2 echo "$0 failed. Exiting."
   exit 1
 elif [ -t 1 ]; then
-  filename=$(basename $exec)
+  filename=$(basename $bin)
   echo "Nix bundle created at $filename."
   cp -f $out $filename
 else