Add postgresql.get_version() function

rattail_fabric2/postgresql.py

@@ -25,6 +25,7 @@ Fabric Library for PostgreSQL
 """
 
 import os
+import re
 
 from rattail_fabric2 import apt
 
@@ -36,6 +37,16 @@ def install(c):
     apt.install(c, 'postgresql')
 
 
+def get_version(c):
+    """
+    Fetch the version of PostgreSQL running on the target system
+    """
+    result = c.run('psql --version', warn=True)
+    if not result.failed:
+        match = re.match(r'^psql \(PostgreSQL\) (\d+\.\d+)(?:\.\d+)?', result.stdout.strip())
+        if match:
+            return float(match.group(1))
+
 def restart(c):
     """
     Restart the PostgreSQL database service