Eskil can compare versions in revision control systems.
Currently RCS, CVS and ClearCase are supported.

If you specify only one file on the command line to Eskil, it will
automatically detect if the file is under revision control and enter
revision control mode.

By default the local file is compared against the latest checked in version,
which is the simple case when you just want to know what you have changed
before checking in.

You can use the -r option to select which version to compare.  It works
like it does in "cvs diff". Examples:

eskil file.txt
  Compare file.txt with the latest checked in version.
eskil -r rev file.txt
  Compare file.txt with the specified version.
eskil -r rev1 -r rev2 file.txt
  Compare the two revisions. This does not involve the local copy of file.txt.


For RCS and CVS version numbers to -r are rather straightforward since they
work just like for -r to them.

For ClearCase there are more possibilities.
ClearCase stream names are build like file paths and in -r you can access the
streams similar to how you find files.
Your current stream is the "current directory".
-r 5                    : Version 5 in current stream.
-r .                    : Latest version in current stream.
-r /full/path/stream/4  : The identified version.
-r /full/path/stream    : Latest version in that stream.
-r ../5                 : Version in parent stream.
-r ..                   : Latest in parent stream.
-r stream/5             : Version in stream, anywhere in tree.
-r stream               : Latest in stream, anywhere in tree.

