NAME
diff - differential file and directory comparator

SYNOPSIS
diff [ -l ] [ -r ] [ -s ] [ -cefhn ] [ -biwt ] dir1 dir2
diff [ -cefhn ] [ -biwt ] file1 file2
diff [ -Dstring ] [ -biw ] file1 file2

DESCRIPTION
If both arguments are directories, diff sorts the contents of the
directories by name, and then runs the regular file diff algorithm
(described below) on text files which are different. Binary files
which differ, common subdirectories, and files which appear in only
one directory are listed. Options when comparing directories are:

-l long output format; each text file diff is piped through pr(1)
to paginate it, other differences are remembered and
summarized after all text file differences are reported.

-r causes application of diff recursively to common
subdirectories encountered.

-s causes diff to report files which are the same, which are
otherwise not mentioned.

-Sname
starts a directory diff in the middle beginning with file
name.

When run on regular files, and when comparing text files which
differ during directory comparison, diff tells what lines must be
changed in the files to bring them into agreement. Except in rare
circumstances, diff finds a smallest sufficient set of file
differences. If neither file1 nor file2 is a directory, then
either may be given as ‘-’, in which case the standard input is
used. If file1 is a directory, then a file in that directory whose
file-name is the same as the file-name of file2 is used (and vice
versa).

There are several options for output format; the default output
format contains lines of these forms:

n1 a n3,n4
n1,n2 d n3
n1,n2 c n3,n4

These lines resemble ed commands to convert file1 into file2. The
numbers after the letters pertain to file2. In fact, by exchanging
‘a’ for ‘d’ and reading backward one may ascertain equally how to
convert file2 into file1. As in ed, identical pairs where n1 = n2
or n3 = n4 are abbreviated as a single number.

Following each of these lines come all the lines that are affected
in the first file flagged by ‘<’, then all the lines that are
affected in the second file flagged by ‘>’.

Except for -b, -w, -i or -t which may be given with any of the
others, the following options are mutually exclusive:

-e produces a script of a, c and d commands for the editor
ed, which will recreate file2 from file1. In connection
with -e, the following shell program may help maintain
multiple versions of a file. Only an ancestral file ($1)
and a chain of version-to-version ed scripts ($2,$3,...)
made by diff need be on hand. A ‘latest version’ appears
on the standard output.

(shift; cat $*; echo ’1,$p’) | ed - $1

Extra commands are added to the output when comparing
directories with -e, so that the result is a sh(1) script
for converting text files which are common to the two
directories from their state in dir1 to their state in
dir2.

-f produces a script similar to that of -e, not useful with
ed, and in the opposite order.

-n produces a script similar to that of -e, but in the
opposite order and with a count of changed lines on each
insert or delete command. This is the form used by
rcsdiff(1).

-c produces a diff with lines of context. The default is to
present 3 lines of context and may be changed, e.g to 10,
by -c10. With -c the output format is modified slightly:
the output beginning with identification of the files
involved and their creation dates and then each change is
separated by a line with a dozen *’s. The lines removed
from file1 are marked with ‘- ’; those added to file2 are
marked ‘+ ’. Lines which are changed from one file to the
other are marked in both files with with ‘! ’.

Changes which lie within <context> lines of each other are
grouped together on output. (This is a change from the
previous "diff -c" but the resulting output is usually
much easier to interpret.)

-h does a fast, half-hearted job. It works only when changed
stretches are short and well separated, but does work on
files of unlimited length.

-Dstring causes diff to create a merged version of file1 and file2
on the standard output, with C preprocessor controls
included so that a compilation of the result without
defining string is equivalent to compiling file1, while
defining string will yield file2.

-b causes trailing blanks (spaces and tabs) to be ignored,
and other strings of blanks to compare equal.

-w is similar to -b but causes whitespace (blanks and tabs)
to be totally ignored. E.g., "if ( a == b )" will
compare equal to "if(a==b)".

-i ignores the case of letters. E.g., "A" will compare
equal to "a".

-t will expand tabs in output lines. Normal or -c output
adds character(s) to the front of each line which may
screw up the indentation of the original source lines and
make the output listing difficult to interpret. This
option will preserve the original source’s indentation.

FILES
/tmp/d?????
/usr/lib/diffh for -h
/bin/diff for directory diffs
/bin/pr

SEE ALSO
cmp(1), cc(1), comm(1), ed(1), diff3(1)

DIAGNOSTICS
Exit status is 0 for no differences, 1 for some, 2 for trouble.

BUGS
Editing scripts produced under the -e or -f option are naive about
creating lines consisting of a single ‘.’.

When comparing directories with the -b, -w or -i options specified,
diff first compares the files ala cmp, and then decides to run the
diff algorithm if they are not equal. This may cause a small
amount of spurious output if the files then turn out to be
identical because the only differences are insignificant blank
string or case differences.