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Comparing and Merging Files with GNU diff and patch
by David MacKenzie, Paul Eggert, and Richard Stallman
Paperback (6"x9"), 120 pages
ISBN 0954161750
RRP £12.95 ($19.95)

"Well packaged... the quality of information is excellent" --- Linux User and Developer Magazine (Issue 36, Feb 2004) Get a printed copy>>> Detailed Description of Unified Format

The unified output format starts with a two-line header, which looks like this:

--- from-file from-file-modification-time
+++ to-file to-file-modification-time

The time stamp looks like ‘2002-02-21 23:30:39.942229878 -0800’ to indicate the date, time with fractional seconds, and time zone.

You can change the header's content with the --label=label option; see See section 2.3.4 Showing Alternate File Names.

Next come one or more hunks of differences; each hunk shows one area where the files differ. Unified format hunks look like this:

@@ from-file-range to-file-range @@

The lines common to both files begin with a space character. The lines that actually differ between the two files have one of the following indicator characters in the left print column:

A line was added here to the first file.
A line was removed here from the first file.
ISBN 0954161750Comparing and Merging Files with GNU diff and patchSee the print edition