The "diff" command:

Usage: fossil diff|gdiff ?OPTIONS? ?FILE1? ?FILE2 ...?

Show the difference between the current version of each of the FILEs specified (as they exist on disk) and that same file as it was checked out. Or if the FILE arguments are omitted, show the unsaved changes currently in the working check-out.

If the "--from VERSION" or "-r VERSION" option is used it specifies the source check-in for the diff operation. If not specified, the source check-in is the base check-in for the current check-out.

If the "--to VERSION" option appears, it specifies the check-in from which the second version of the file or files is taken. If there is no "--to" option then the (possibly edited) files in the current check-out are used.

The "--checkin VERSION" option shows the changes made by check-in VERSION relative to its primary parent.

The "-i" command-line option forces the use of the internal diff logic rather than any external diff program that might be configured using the "setting" command. If no external diff program is configured, then the "-i" option is a no-op. The "-i" option converts "gdiff" into "diff".

The "-v" or "--verbose" option causes the complete text of added or deleted files to be displayed. -N and --new-file are aliases for verbose mode.

The "--diff-binary" option enables or disables the inclusion of binary files when using an external diff program.

The "--binary" option causes files matching the glob PATTERN to be treated as binary when considering if they should be used with external diff program. This option overrides the "binary-glob" setting.

Options:

--binary PATTERN
Treat files that match the glob PATTERN as binary
--branch BRANCH
Show diff of all changes on BRANCH
--brief
Show filenames only
-b|--browser
Show the diff output in a web-browser
--by
Shorthand for "--browser -y"
--checkin VERSION
Show diff of all changes in VERSION
--command PROG
External diff program. Overrides "diff-command"
-c|--context N
Use N lines of context
--diff-binary BOOL
Include binary files with external commands
--exec-abs-paths
Force absolute path names on external commands
--exec-rel-paths
Force relative path names on external commands
-r|--from VERSION
Select VERSION as source for the diff
-w|--ignore-all-space
Ignore white space when comparing lines
-i|--internal
Use internal diff logic
-N|--new-file
Alias for --verbose
--numstat
Show only the number of lines delete and added
-y|--side-by-side
Side-by-side diff
--strip-trailing-cr
Strip trailing CR
--tclsh PATH
Tcl/Tk used for --tk (default: "tclsh")
--tk
Launch a Tcl/Tk GUI for display
--to VERSION
Select VERSION as target for the diff
--undo
Diff against the "undo" buffer
--unified
Unified diff
-v|--verbose
Output complete text of added or deleted files
--webpage
Format output as a stand-alone HTML webpage
-W|--width N
Width of lines in side-by-side diff
-Z|--ignore-trailing-space
Ignore changes to end-of-line whitespace