These variables specify the programs to use to produce differences and do patching.

These variables specify the options to pass to the above utilities.

In ediff-diff-options, it may be useful to specify options such as `-w' that ignore certain kinds of changes. However, Ediff does not let you use the option `-c', as it doesn't recognize this format yet.

The program to use to apply patches. Since there are certain incompatibilities between the different versions of the patch program, the best way to stay out of trouble is to use a GNU-compatible version. Otherwise, you may have to tune the values of the variables ediff-patch-options, ediff-backup-specs, and ediff-backup-extension as described below.

Note: the `-b' and `-z' options should be specified in `ediff-backup-specs', not in ediff-patch-options.

It is recommended to pass the `-f' option to the patch program, so it won't ask questions. However, some implementations don't accept this option, in which case the default value of this variable should be changed.

Backup extension used by the patch program. Must be specified, even if ediff-backup-specs is given.

Some versions of the patch program let the user specify `-b backup-extension'. Other versions only permit `-b', which (usually) assumes the extension `.orig'. Yet others force you to use `-z<backup-extension>'.

Note that both `ediff-backup-extension' and `ediff-backup-specs' must be properly set. If your patch program takes the option `-b', but not `-b extension', the variable `ediff-backup-extension' must still be set so Ediff will know which extension to use.

Because Ediff limits the options you may want to pass to the diff program, it partially makes up for this drawback by letting you save the output from diff in your preferred format, which is specified via the above two variables.

The output generated by ediff-custom-diff-program (which doesn't even have to be a standard-style `diff'!) is not used by Ediff. It is provided exclusively so that you can refer to it later, send it over email, etc. For instance, after reviewing the differences, you may want to send context differences to a colleague. Since Ediff ignores the `-c' option in ediff-diff-program, you would have to run diff -c separately just to produce the list of differences. Fortunately, ediff-custom-diff-program and ediff-custom-diff-options eliminate this nuisance by keeping a copy of a difference list in the desired format in a buffer that can be displayed via the command D.

Specifies the default directory to look for patches.