+This directory contains the GNU DIFF and DIFF3 utilities, version 1.15.
+See file COPYING for copying conditions. To compile and install on
+system V, you must edit the makefile according to comments therein.
+
+Report bugs to bug-gnu-utils@prep.ai.mit.edu
+
+Version 1.15 has the following new features; please see below for details.
+
+ -L (+file-label) option
+ -u (+unified) option
+ -a and -m options for diff3
+ Most output styles can represent incomplete input lines.
+ `Text' is defined by ISO 8859.
+ diff3 exit status 0 means success, 1 means overlaps, 2 means trouble.
+
+
+This version of diff provides all the features of BSD's diff.
+It has these additional features:
+
+ An input file may end in a non-newline character. If so, its last
+ line is called an incomplete line and is distinguished on output
+ from a full line. In the default, -c, and -u output styles, an
+ incomplete output line is followed by a diagnostic line that starts
+ with \. With -n, an incomplete line is output without a trailing
+ newline. Other output styles (-D, -e, -f) cannot represent an
+ incomplete line, so they pretend that there was a newline, and -e and -f
+ also print an error message. For example, suppose F and G are one-byte
+ files that contain just ``f'' and ``g'', respectively.
+
+ Then ``diff F G'' outputs
+
+ 1c1
+ < f
+ \ No newline at end of file
+ ---
+ > g
+ \ No newline at end of file
+
+ (The exact diagnostic message may differ, e.g. for non-English locales.)
+ ``diff -n F G'' outputs the following without a trailing newline:
+
+ d1 1
+ a1 1
+ g
+
+ ``diff -e F G'' sends two diagnostics to stderr and the following to stdout:
+
+ 1c
+ g
+ .
+
+ A file is considered to be text if its first characters are all in the
+ ISO 8859 character set; BSD's diff uses Ascii.
+
+ GNU DIFF has the following additional options:
+
+ -a Always treat files as text and compare them line-by-line,
+ even if they do not appear to be text.
+
+ -B ignore changes that just insert or delete blank lines.
+
+ -C #
+ request -c format and specify number of context lines.
+
+ -F regexp
+ in context format, for each unit of differences, show some of
+ the last preceding line that matches the specified regexp.
+
+ -H use heuristics to speed handling of large files that
+ have numerous scattered small changes. The algorithm becomes
+ asymptotically linear for such files!
+
+ -I regexp
+ ignore changes that just insert or delete lines that
+ match the specified regexp.
+
+ -L label
+ Use the specified label in file header lines output by the -c option.
+ This option may be given zero, one, or two times,
+ to affect neither label, just the first file's label, or both labels.
+ A file's default label is its name, a tab, and its modification date.
+
+ -N in directory comparison, if a file is found in only one directory,
+ treat it as present but empty in the other directory.
+
+ -p equivalent to -c -F'^[_a-zA-Z]'. This is useful for C code
+ because it shows which function each change is in.
+
+ -T print a tab rather than a space before the text of a line
+ in normal or context format. This causes the alignment
+ of tabs in the line to look normal.
+
+ -u[#]
+ produce unified style output with # context lines (default 3).
+ This style is like -c, but it is more compact because context
+ lines are printed only once. Lines from just the first file
+ are marked '-'; lines from just the second file are marked '+'.
+
+This version of diff3 has all of BSD diff3's features, with the following
+additional features.
+
+ An input file may end in a non-newline character. With the -m option,
+ an incomplete last line stays incomplete. Other output styles treat
+ incomplete lines like diff.
+
+ The file name '-' denotes the standard input. It can appear at most once.
+
+ diff3 has the following additional options:
+
+ -a Always treat files as text and compare them line-by-line,
+ even if they do not appear to be text.
+
+ -i Include 'w' and 'q' commands at the end of the output, to write out
+ the changed file, thus emulating system V behavior. One of the edit
+ script options -e, -E, -x, -X, -3 must also be specified.
+
+ -m Apply the edit script to the first file and send the result to
+ standard output. Unlike piping diff3's output to ed(1), this works
+ even for binary files and incomplete lines. -E is assumed if no edit
+ script option is specified. This option is incompatible with -i.
+
+ -L label
+ Use the specified label for lines output by the -E and -X options,
+ one of which must also be specified. This option may be given zero,
+ one, or two times; the first label marks <<<<<<< lines and the second
+ marks >>>>>>> lines. The default labels are the names of the first and
+ third files on the command line. Thus ``diff3 -L X -L Z -E A B C''
+ acts like ``diff3 -E A B C'', except that the output looks like it
+ came from files named X and Z rather than from files named A and C.
+
+ Exit status 0 means success, 1 means overlaps were found and -E or -X was
+ specified, and 2 means trouble.
+
+
+
+GNU DIFF was written by Mike Haertel, David Hayes, Richard Stallman
+and Len Tower. The basic algorithm is described in: "An O(ND)
+Difference Algorithm and its Variations", Eugene Myers, Algorithmica
+Vol. 1 No. 2, 1986, p 251.
+
+Many bugs were fixed by Paul Eggert. The unified diff idea and format
+are from Wayne Davison.
+
+Suggested projects for improving GNU DIFF:
+
+* Handle very large files by not keeping the entire text in core.
+
+One way to do this is to scan the files sequentally to compute hash
+codes of the lines and put the lines in equivalence classes based only
+on hash code. Then compare the files normally. This will produce
+some false matches.
+
+Then scan the two files sequentially again, checking each match to see
+whether it is real. When a match is not real, mark both the
+"matching" lines as changed. Then build an edit script as usual.
+
+The output routines would have to be changed to scan the files
+sequentially looking for the text to print.
projects / unix-history / commitdiff