Any way to use a custom diff tool with cleartool/clearcase?

I'd like to use my own diff when working in a clearcase snapshot view.

As far as I can see, there is no way to specify a diff tool when running "cleartool diff", so I was thinking I could run something like "mydiff <predecessor file> <modified file in my view>", but I don't know enough about ClearCase to be able to find the "predecessor file" to diff against.

Any way to do this?

Forgot to mention (until now, after reading the first two responses dealing with windows) that this is on Unix, and I am not allowed to muck with the ClearCase configuration.

How to change default diff tools

You can specify an external diff tool by modifying the file map, in "c:\program files\rational\ClearCase\lib\mgrs"

The WinMerge suggested by Paul actually modifies that file.

Each map line has 3 parts: the CC filetype, the CC action, and the application.

Find the section in the map file for text_file_delta file types. There you will find lines for CC actions compare, xcompare, merge, and xmerge which look like this:

text_file_delta   compare          ..\..\bin\cleardiff.exe
text_file_delta   xcompare         ..\..\bin\cleardiffmrg.exe
text_file_delta   merge            ..\..\bin\cleardiff.exe
text_file_delta   xmerge           ..\..\bin\cleardiffmrg.exe

You can replace them by the executable of your diff tool choice.

Or, a simple diff script

If you want to go full command-line on this (which I like ;-) ), a little ccperl can help:

#!/bin/perl
my ($file, $switches) = @ARGV;
$switches ||= '-ubBw';

my ($element, $version, $pred) 
    = split(/;/,`cleartool describe -fmt '%En;%Vn;%PVn' $file`);

unless ($pred) { die "ctdiff: $file has no predecessor\n"; }

exec "mydiff $switches $element\@\@$pred $file";

Warning: extended pathname (@@\...) is only accessible in dynamic view (M:\..., not snapshot view (c:\...).

The script has nothing to do with the mapfile presented above:

• that file defines 'Type Merge Managers'.
• This script allows you to run any merge manager on any file you want, without reading any map file to look for the right diff exe to use for a given file.

Here, you provide to the script both informations: the file (as a parameter) and the diff exe to run (within the script implementation: replace mydiff by whatever diff exe you want).

Or, improved diff script (works in static/snapshot views too)

Here is a version of this script which works for both snapshot and dynamic view.

For snapshot view, I use the chacmool's suggestion: cleartool get.

Again, you can replace the diff command included in this script by the tool of your choosing.

#!/bin/perl
my ($file, $switches) = @ARGV;
$switches ||= '-u';

my ($element, $version, $pred) 
    = split(/;/,`cleartool describe -fmt '%En;%Vn;%PVn' $file`);

unless ($pred) { die "ctdiff: $file has no predecessor\n"; }

# figure out if view is dynamic or snapshot
my $str1 = `cleartool lsview -long -cview`;
if($? == 0) { dodie("pred.pl must be executed within a clearcase view"); }
my @ary1 = grep(/Global path:/, split(/\n/, $str1));
if($str1 =~ /View attributes: snapshot/sm) { $is_snapshot = 1; }

my $predfile = "$element\@\@$pred";
$predfile =~ s/\'//g;#'
#printf("$predfile\n");
if ($is_snapshot) { 
  my $predtemp = "c:\\temp\\pred.txt";
  unlink($predtemp);
  my $cmd = "cleartool get -to $predtemp $predfile"; printf("$cmd\n");
  my $str2 = `$cmd`;
  $predfile = $predtemp;
}
sub dodie {
    my $message = $_[0];
    print($message . "\n");
    exit 1;
}

exec "diff $switches $predfile $file";

Another option is to use Git+ClearCase (or see this or this) and just diff with Git.

This is remarkably easy to set up and, in my experience, it actually hurts your brain less to use two VCS systems at once than to try to beat CC into being a 21st century tool.

Just think of Git as a bridge between CC and diff :-)

It seems someone already thought about it on snip2code!
Here a tcsh bash script that does exactly what you want.

Custom-diff-tool-for-clearcase-object

As you can see the following is the key code to get the previous version of a given file:

cleartool descr -pred -short $1

Where $1 is the file name to compare.

#!/bin/tcsh -e
set _CLEARCASE_VIEW = `cleartool pwv -short -setview`
echo Set view: "$_CLEARCASE_VIEW"
set my_firstversion = ""
set my_secondversion = ""
set my_difftool = kdiff3

# check clearcase view
if ( "$_CLEARCASE_VIEW" == "** NONE **" ) then
  echo "Error: ClearCase view not set, aborted."
  exit -1
endif

if ( "$1" == "" ) then
  echo "Error: missing 1st file argument!"
  echo "Eg: `basename $0` file1.txt -> This will diff file1.txt with its previous version"
  echo "Eg: `basename $0` file1.txt file2.txt -> This will diff file1.txt and file2.txt"
  exit -1
endif  

set my_firstversion = "$1"
echo "my_firstversion=$my_firstversion"

if ( "$2" == "" ) then
  echo "No 2nd file passed, calculating previous version of $my_firstversion"
  set my_secondversion = $my_firstversion@@`cleartool descr -pred -short $my_firstversion`
else
  echo "Setting 2nd file to $2"
  set my_secondversion = "$2"
endif
echo "my_secondversion=$my_secondversion"

${my_difftool} ${my_firstversion} ${my_secondversion} &