diff(1) diff(1)
NAME
diff - differential file and directory comparator
SYNOPSIS
diff [-l] [-r] [-s] [-Sname] [-cefh] [-b] dir1 dir2
diff [-cefh] [-b] file1 file2
diff [-Dstring] [-b] 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. Flag 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 filename
is the same as the filename of file2 is used (and vice
versa).
There are several flag 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
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diff(1) diff(1)
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, which may be given with any of the others,
the following flag options are mutually exclusive:
-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
``!''.
-e producing 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. Since such a shell
script is useful only in a file that you may run on
other files, it is best to redirect the output of
this command into a file.
-f produces a script similar to that of -e, not useful
with ed, and in the opposite order.
-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.
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-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.
FILES
/usr/bin/diff
/tmp/d?????
/usr/lib/diffh for -h
/bin/pr
SEE ALSO
cmp(1), cc(1), comm(1), ed(1), diff3(1),
``Other tools'' in Oreo Programming Languages and Tools,
Volume 2.
DIAGNOSTICS
Exit status is 0 for no differences, 1 for some, 2 for
trouble.
BUGS
Editing scripts produced under the -e or -f flag option are
naive about creating lines consisting of a single `.'.
When comparing directories with the -b flag option
specified, diff first compares the files as with 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 differences.
If an unrecognized flag option is specified, diff performs
the default operation anyway.
diff may not work if files contain very long lines, of if
files are very long.
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