From edb12501bde8baed7b6ed6c786dac15f065c40d5 Mon Sep 17 00:00:00 2001
From: Dorian Pula <dorian.pula@amber-penguin-software.ca>
Date: Mon, 18 Nov 2013 07:44:03 -0500
Subject: [PATCH] Added a quick but useful script to compare the state of one
 Debian system against another.

---
 debian_dpkg_compare.py | 57 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)
 create mode 100644 debian_dpkg_compare.py

diff --git a/debian_dpkg_compare.py b/debian_dpkg_compare.py
new file mode 100644
index 0000000..c31e875
--- /dev/null
+++ b/debian_dpkg_compare.py
@@ -0,0 +1,57 @@
+import re
+import subprocess
+import sys
+
+
+def main():
+    """Get information about the Debian packages in an older system and the current system or another system."""
+
+    if len(sys.argv) > 2:
+        new_file_info = read_in_dpkg_listing_output_file(sys.argv[2])
+        new_pkgs = parse_package_listing(new_file_info)
+    else:
+        packager_output, _ = gather_dpkg_package_listing()
+        new_pkgs = parse_package_listing(packager_output.splitlines())
+
+    old_file_info = read_in_dpkg_listing_output_file(sys.argv[1])
+    old_pkgs = parse_package_listing(old_file_info)
+
+    # Cause dicts are great, but never are they sorted
+    old_pkg_names = old_pkgs.keys()
+    old_pkg_names.sort()
+
+    print("Old packages not in new system...")
+    for pkg in old_pkg_names:
+        if pkg not in new_pkgs:
+            print("{}\n\t\t\t\t{}".format(pkg, old_pkgs[pkg]))
+
+
+def parse_package_listing(listing):
+    """Parse the package listing from the given list."""
+    pkg = {}
+    counter = 0
+    for pkg_info_line in listing:
+        counter += 1
+        if counter > 5:
+            pkg_info = pkg_info_line.split()
+            pkg_name = pkg_info[1]
+            pkg_version = pkg_info[2]
+            pkg[pkg_name] = pkg_version
+    return pkg
+
+
+def gather_dpkg_package_listing():
+    """Run dpkg -l and gather in input."""
+    list_pkgs_process = subprocess.Popen(["dpkg", "-l"], stdout=subprocess.PIPE)
+    return list_pkgs_process.communicate()
+
+
+def read_in_dpkg_listing_output_file(filename):
+    """Reads in a text file with output from dpkg -l."""
+    with open(filename, "r") as input_file:
+            file_contents = input_file.readlines()
+    return file_contents
+
+
+if __name__ == '__main__':
+    main()