adding a
adding b
Only in a: a
Only in a: b
diffing a.000000000000 a
hg falabala [OPTION]... [FILE]...

use 'echo' to diff repository (or selected files)

    Show differences between revisions for the specified files, using the
    'echo' program.

    When two revision arguments are given, then changes are shown between
    those revisions. If only one revision is specified then that revision is
    compared to the working directory, and, when no revisions are specified,
    the working directory files are compared to its parent.

options:

 -o --option   pass option to comparison program
 -r --rev      revision
 -c --change   change made by revision
 -I --include  include names matching the given patterns
 -X --exclude  exclude names matching the given patterns

use "hg -v help falabala" to show global options
diffing a.8a5febb7f867/a a.34eed99112ab/a
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
created new head
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
(branch merge, don't forget to commit)
diffing a.2a13a4d2da36/a [tmp]/test-extdiff/a/a
diffing a.8a5febb7f867/a a.34eed99112ab/a
diffing a.2a13a4d2da36/a a.46c0e4daeb72/a
diff-like tools yield a non-zero exit code

% test extdiff of multiple files in tmp dir:
% diff in working directory, before
diff --git a/a b/a
--- a/a
+++ b/a
@@ -1,1 +1,1 @@
-a
+changed
diff --git a/b b/b
old mode 100644
new mode 100755
--- a/b
+++ b/b
@@ -1,1 +1,1 @@
-b
+changed
% edit with extdiff -p
% diff in working directory, after
diff --git a/a b/a
--- a/a
+++ b/a
@@ -1,1 +1,2 @@
-a
+changed
+edited
diff --git a/b b/b
old mode 100644
new mode 100755
--- a/b
+++ b/b
@@ -1,1 +1,2 @@
-b
+changed
+edited

% test extdiff with --option
this a.8a5febb7f867/a a.34eed99112ab/a
diffing this a.8a5febb7f867/a a.34eed99112ab/a