The specification for "diff" is as specified in the SUS but with the following differences as listed below.
If an argument is the absolute file name of a disk device node containing a mounted filesystem, df shows the space available on that filesystem rather than on the filesystem containing the device node (which is always the root filesystem)
Treat all files as text and compare them line-by- line, even if they do not seem to be text.
Ignore changes that just insert or delete blank lines.
Report only whether the files differ, not the details of the differences.
Equivalent to the -C option as specified in the SUS.
Change the algorithm to perhaps find a smaller set of changes. This makes diff slower (sometimes much slower).
Make merged if-then-else output, conditional on the preprocessor macro name.
Equivalent to the -e option as specified in the SUS
When comparing directories, ignore files and subdirectories whose basenames match pattern.
When comparing directories, ignore files and subdirectories whose basenames match any pattern contained in file.
Expand tabs to spaces in the output, to preserve the alignment of tabs in the input files.
In context and unified , for each hunk of differences, show some of the last preceding line that matches regexp.
Make output that looks vaguely like an ed script but has changes in the order they appear in the file.
Use heuristics to speed handling of large files that have numerous scattered small changes.
Do not discard the last lines lines of the common prefix and the first lines lines of the common suffix.
Ignore changes in case; consider upper and lower case letters equivalent.
Ignore changes that just insert or delete lines that match regexp.
Make merged if-then-else output, conditional on the preprocessor macro name.
Ignore white space when comparing lines.
Ignore changes in case; consider upper and lower case to be the same.
Ignore changes that just insert or delete lines that match regexp.
Ignore changes in amount of white space.
Output a tab rather than a space before the text of a line in normal or context . This causes the alignment of tabs in the line to look normal.
Pass the output through pr to paginate it.
Ignore changes in case; consider upper and lower case to be the same.