diff --git a/IPython/Extensions/ipy_which.py b/IPython/Extensions/ipy_which.py
new file mode 100644
index 0000000..73de12c
--- /dev/null
+++ b/IPython/Extensions/ipy_which.py
@@ -0,0 +1,70 @@
+r""" %which magic command
+
+%which <cmd> => search PATH for files matching PATH. Also scans aliases
+
+"""
+
+import IPython.ipapi
+ip = IPython.ipapi.get()
+
+import os,sys
+from fnmatch import fnmatch
+def which(fname):
+    fullpath = filter(os.path.isdir,os.environ['PATH'].split(os.pathsep))
+    
+    if '.' not in fullpath:
+        fullpath = ['.'] + fullpath
+    fn = fname
+    for p in fullpath:
+        for f in os.listdir(p):
+            head, ext = os.path.splitext(f)
+            if f == fn or fnmatch(head, fn):
+                yield os.path.join(p,f)
+    return
+
+def which_alias(fname):
+    for al, tgt in ip.IP.alias_table.items():
+        if not (al == fname or fnmatch(al, fname)):
+            continue
+        trg = tgt[1]
+        
+        trans = ip.expand_alias(trg)
+        cmd = trans.split(None,1)[0]
+        print al,"->",trans
+        for realcmd in which(cmd):
+            print "  ==",realcmd
+        
+def which_f(self, arg):
+    r""" %which <cmd> => search PATH for files matching cmd. Also scans aliases.
+
+    Traverses PATH and prints all files (not just executables!) that match the
+    pattern on command line. Probably more useful in finding stuff
+    interactively than 'which', which only prints the first matching item.
+    
+    Also discovers and expands aliases, so you'll see what will be executed
+    when you call an alias.
+    
+    Example:
+    
+    [~]|62> %which d
+    d -> ls -F --color=auto
+      == c:\cygwin\bin\ls.exe
+    c:\cygwin\bin\d.exe
+    
+    [~]|64> %which diff*
+    diff3 -> diff3
+      == c:\cygwin\bin\diff3.exe
+    diff -> diff
+      == c:\cygwin\bin\diff.exe
+    c:\cygwin\bin\diff.exe
+    c:\cygwin\bin\diff3.exe
+
+    """
+    
+    which_alias(arg)
+
+    for e in which(arg):
+        print e
+    
+ip.expose_magic("which",which_f)        
+        
diff --git a/IPython/UserConfig/ipy_profile_sh.py b/IPython/UserConfig/ipy_profile_sh.py
index 876709a..3722b2a 100644
--- a/IPython/UserConfig/ipy_profile_sh.py
+++ b/IPython/UserConfig/ipy_profile_sh.py
@@ -31,6 +31,7 @@ def main():
     
     # beefed up %env is handy in shell mode
     import envpersist
+    import ipy_which
     
     
     ip.ex('import os')
diff --git a/IPython/ipapi.py b/IPython/ipapi.py
index 7595c68..5f54e82 100644
--- a/IPython/ipapi.py
+++ b/IPython/ipapi.py
@@ -300,6 +300,7 @@ class IPApi:
         
         pre,fn,rest = self.IP.split_user_input(line)
         res = pre + self.IP.expand_aliases(fn,rest)
+        return res
 
     def defalias(self, name, cmd):
         """ Define a new alias
diff --git a/doc/ChangeLog b/doc/ChangeLog
index ad463a9..f328793 100644
--- a/doc/ChangeLog
+++ b/doc/ChangeLog
@@ -1,3 +1,12 @@
+2007-04-25  Ville Vainio  <vivainio@gmail.com>
+
+	* Extensions/ipy_which.py: added extension for %which magic, works
+	a lot like unix 'which' but also finds and expands aliases, and
+	allows wildcards.
+
+	* ipapi.py (expand_alias): Now actually *return* the expanded alias,
+	as opposed to returning nothing.
+
 2007-04-22  Jörgen Stenarson  <jorgen.stenarson@bostream.nu>
 
 	* Fix bug in iplib.py/safe_execfile when launching ipython with a script like ipython.py foo.py