Show the difference between two text files (or all files with the same names in two directories).
diff [options] from_file to_file
-a treats all files as text even if they aren’t text files.
-b ignores blank lines and repeated blanks.
-c produces output in a different format.
-d tries to find a smaller set of changes (this makes diff slower).
-e produces a script for the ed editor to convert from_file to to_file.
-f produces output similar to that of -e, but in reverse order.
-i ignores case.
-l passes the output to the pr command to paginate it.
-n works like -f, but counts the number of changed lines.
-r recursively compares files with the same name in all subdirectories.
-s reports when two files are the same.
-t expands tabs to spaces in the output.
-u uses the unified output format.
-v displays the version of diff.
-w ignores spaces and tabs when comparing lines.
The diff command compares from_file with to_file and displays the lines that differ. The output is in a format the patch command can use to convert from_file to to_file.