diff(1) General Commands Manual diff(1)
diff - differential file comparator
diff [options] dir1 dir2
diff [options] file1 file2
The command compares the contents of files or groups of files, and lists any differences it finds. When run on regular files, and when com-
paring text files that differ during directory comparison, tells what lines must be changed in the files to bring them into agreement.
Except in rare circumstances, finds a smallest sufficient set of file differences. If neither file1 nor file2 is a directory, then either
can be specified 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 likewise if file2 is a directory.
If both arguments are directories, sorts the contents of the directories by name, and then runs the regular file algorithm on text files
that are different. Binary files that differ, common subdirectories, and files that appear in only one directory are listed.
The following options are used when comparing directories:
-l Displays the output in long format. Each text file is piped through to paginate it; other differences are summarized after all
text file differences are reported.
-n Produces a script similar to that of -e, but in reverse order and with a count of changed lines on each insert or delete command.
-r Recursively checks files in common subdirectories.
-s Displays names of files that are the same.
-Sname Starts a directory in the middle beginning with the specified file.
Except for the -b, i, t, and w options, which may be given with any of the others, the following formatting options are mutually exclusive:
-b Ignores trailing blanks and other strings of blanks and treats such portions as equal.
-c Displays three context lines with each output line. For backwards compatibility, -cn causes n number of context lines.
-C n Displays specified number of context lines with each output line. With -c or -C the output format is modified slightly: the out-
put begins with identification of the files involved and their creation dates and then each change is separated by a line with a
dozen asterisks (*). The lines removed from file1 are marked with minus sign (-); those added to file2 are marked plus sign (+).
Lines that are changed from one file to the other are marked in both files with an exclamation point (!).
Changes within n context lines of each other are grouped together in the output. This results in output that is usually much
easier to interpret.
-Dstring Causes to create a merged version of file1 and file2 on the standard output. With C preprocessor controls included, a compila-
tion of the result without defining string is equivalent to compiling file1, while defining string will yield file2.
-e Writes output to an script. In connection with -e, the following shell program can help maintain multiple versions of a file.
Only an ancestral file ($1) and a chain of version-to-version scripts ($2,$3,...) made by need be available. A latest version
message appears on the standard output.
(shift; cat $*; echo '1,$p') | ed - $1
If you specify -e when comparing directories the result is a script for converting text files that are common to the two directo-
ries from their state in dir1 to their state in dir2.
-f Writes the output in reverse order to a script.
-h Makes a hasty comparison. It works only when changed portions are short and well separated, but does work on files of unlimited
-i Ignores the case of letters. For example 'A' will compare equal to `a'.
-t Expand tabs in output lines. Normal or -c output adds character(s) to the front of each line which may affect the indentation of
the original source lines and make the output listing difficult to interpret. This option will preserves the original indenta-
-w Causes whitespace (blanks and tabs) to be totally ignored. For example, `if ( a == b )' will compare equal to `if(a==b)'.
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 commands to convert file1 into file2. The numbers after the letters pertain to file2. In fact, by exchanging `a' for
`d' and reading backward you can tell how to convert file2 into file1. As in identical pairs where n1 = n2 or n3 = n4 are abbreviated as a
Following each of these lines come all the lines that are affected in the first file flagged by a left angle bracket (<). Then all the
lines that are affected in the second file are listed, flagged by a right angle bracket (>).
Editing scripts produced under the -e or -f option have trouble creating lines consisting of a single period (.).
When comparing directories with the -b, i, t, or w options specified, first compares the files as does, and then runs the algorithm if they
are not equal. If the only differences are in the blank strings, may report these as differences.
Exit status is 0 for no differences, 1 for some differences,and 2 if the specified file cannot be found.
cc(1), cmp(1), comm(1), diff3(1), ed(1)