rpg-unpack for extracting gems and gemspecs

Makefile

@@ -33,14 +33,14 @@ SOURCES = \
 	rpg-install.sh rpg-list.sh rpg-version-test.sh rpg-uninstall.sh \
 	rpg-build.sh rpg-env.sh rpg-update.sh rpg-resolve.sh rpg-upgrade.sh \
 	rpg-steal.sh rpg-fsck.sh rpg-status.sh rpg-outdated.sh \
-	rpg-package-register.sh rpg-package-install.sh rpg-solve.sh
+	rpg-package-register.sh rpg-package-install.sh rpg-solve.sh rpg-unpack.sh
 
 PROGRAMS = \
 	rpg-sh-setup rpg rpg-config rpg-deps rpg-fetch \
 	rpg-install rpg-list rpg-version-test rpg-uninstall \
 	rpg-build rpg-env rpg-update rpg-resolve rpg-upgrade \
 	rpg-steal rpg-fsck rpg-status rpg-outdated rpg-parse-package-list \
-	rpg-package-register rpg-package-install rpg-solve
+	rpg-package-register rpg-package-install rpg-solve rpg-unpack
 
 DOCHTML = \
 	rpg-sh-setup.html rpg.html rpg-config.html rpg-deps.html rpg-fetch.html \

rpg-package-install.sh

@@ -90,7 +90,7 @@ then notice "sources already exist. bypassing fetch and unpack."
 else gemfile=$(rpg-fetch "$package" "$version")
      notice "unpacking $gemfile into $RPGPACKS"
      mkdir -p "$RPGPACKS"
-     (cd "$RPGPACKS" && gem unpack "$gemfile" >/dev/null)
+     rpg-unpack -p "$RPGPACKS" "$gemfile"
 fi
 
 # If the package already has an active/installed version, check if its
@@ -204,7 +204,6 @@ test -d man && {
     done
 }
 
-
 # Mark this package as active
 unlink "$packagedir/installing"
 ln -sf "$version" "$packagedir/active"

rpg-status.sh

@@ -31,7 +31,7 @@ do
     a)   joiner="-a2";;
     u)   update=true;;
     p)   parsey=true;;
-    ?)   echo "$usage"
+    ?)   helpthem;
          exit 2;;
     esac
 done

rpg-unpack.sh

@@ -0,0 +1,75 @@
+#!/bin/sh
+# The `rpg-unpack` program reads the gem file's internal tar-based structure
+# and either untars into a new directory or writes the data segment's tar
+# stream to stdout.
+#
+# Gem files are more or less normal tarballs that looks like this:
+#
+#     $ tar tv < sinatra-0.9.6.gem
+#     -rw-r--r-- wheel/wheel  117190 1969-12-31 16:00:00 data.tar.gz
+#     -rw-r--r-- wheel/wheel    1225 1969-12-31 16:00:00 metadata.gz
+#
+# The `metadata.gz` file is a gzip compressed YAML gemspec. The
+# `data.tar.gz` holds the unprefixed files.
+#
+# There's also an older gem format apparently, but I'm hoping to not have to
+# deal with it.
+set -e
+. rpg-sh-setup
+
+USAGE '${PROGNAME} [-p <path>] <gem>
+       ${PROGNAME} -c [-m] <gem>
+Unpack a gem file to disk or as a tar stream on stdout.
+
+Options
+  -p <path>        Unpack under <path> instead of the working directory
+  -c               Write gem data tar stream to stdout. Do not create any files.
+  -m               Change the behavior of the -c option. Write gem metadata
+                   segment instead of the data segment.'
+workdir=.
+filter=untar
+segment=data.tar.gz
+while getopts cmp: opt
+do
+    case $opt in
+    p)   workdir="$OPTARG";;
+    c)   filter=cat;;
+    m)   segment=metadata.gz;;
+    ?)   helpthem
+         exit 2;;
+    esac
+done
+shift $(( $OPTIND - 1 ))
+
+# Piping the gemspec through tar isn't going to help anyone. Fail fast.
+if test $segment = "metadata.gz" -a $filter = "untar"
+then warn "illegal argument: -m must be used with -c"
+     exit 2
+fi
+
+# Make sure a gem file was given.
+name=$(basename "$1" .gem)
+test "$name" || { helpthem; exit 2; }
+
+# Quickly check that the gem file is readable.
+test -r "$1" || {
+    warn "gem file can not be read: $1"
+    exit 1
+}
+
+# This takes the gem's `data.tar` stream on stdin and untars it into a
+# newly created directory after the gem name. When the `-c` option is not
+# given, the gem tar stream is piped through here.
+untar () {
+    mkdir "$workdir/$name"
+    tar -xom -C "$workdir/$name" -f - 2>/dev/null
+}
+
+# Pipe the gem directly into `tar` and extract only the file/segment we're
+# interested in (the `-O` option causes the file to be written to stdout
+# instead of to disk). Next, pipe that thing through gzip to decompress and
+# finally into whatever filter was configured (`cat` with the `-c` option or
+# our `untar` function above otherwise).
+tar -xOmf - $segment < "$1" 2>/dev/null |
+gzip -dc                                |
+$filter