diff - Compares text files
diff [-c | -C number | -e | -f | -h | -n] [-bilrstw] [-Sfile] direc-
diff [-c | -C number | -e | -f | -h | -n] [-bitw] file1 file2
diff [-Dstring] [-bitw] file1 file2
Interfaces documented on this reference page conform to industry standards
Refer to the standards(5) reference page for more information about indus-
try standards and associated tags.
The -c, -C, -e, -f, -h, and -n options are mutually exclusive.
The -r, -s, and -S options can be specified with directory comparisons
The -b, -i, -l, -t, and -w options can be used in combination with any oth-
ers and in both file and directory comparisons.
-b Causes trailing white space at the end of a line to be treated as a
single newline character.
-c Produces a listing with the default number of lines of context (3
lines). The output lists the files being compared and their last
modification dates, then lists the differing lines. Lines that are
changed from one file to the other are marked in both files with an !
(exclamation point). Changes that lie within the specified number of
lines of each other are grouped together on output.
Produces output that provides number lines of context (where number is
a positive decimal integer).
[Tru64 UNIX] Causes diff to create a merged version of file1 and file2
on the standard output, with C preprocessor controls included. Thus, a
compilation of the result without defining string is equivalent to com-
piling file1, while defining string yields file2.
-e Produces a script of a, c, d, and s commands for the editor ed, which
can recreate file2 from file1. 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 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
[Tru64 UNIX] Extra commands are added to the output when comparing
directories with -e; the result is a sh script for converting text
files common to the directories from their state in directory1 to their
state in directory2.
-f Produces a script similar to that of -e, not useful with ed, and in the
-h [Tru64 UNIX] Performs a faster comparison. This option only works
when the changed sections are short and well separated, but it does
work on files of any length. The -e and -f options are not available
when you use the -h option.
-i [Tru64 UNIX] Ignores the case of letters. For example, A is con-
sidered identical to a.
-l [Tru64 UNIX] Specifies long output format; each text file diff listing
is piped through pr to paginate it, other differences are remembered
and summarized after all text file differences are reported. (Direc-
tory comparisons only.)
-n [Tru64 UNIX] Produces a script similar to that of -e, but in the oppo-
site order and with a count of changed lines on each insert or delete
command. This is the form used by the revision control system (RCS).
-r Checks files in common subdirectories recursively.
-s [Tru64 UNIX] Reports identical files, which are otherwise not men-
[Tru64 UNIX] Starts a directory diff in the middle, beginning with
file. (Directory comparisons only.)
-t [Tru64 UNIX] Expands tabs in output lines. Normal or -c output adds
characters to the front of each line that can affect the indentation of
the original source lines and make the output listing difficult to
interpret. This option preserves the original source's indentation.
-w [Tru64 UNIX] Is similar to -b, but causes whitespace (spaces and tabs)
to be ignored. For example, if ( a == b ) is considered identical to
The path names of files or directories to be compared. See the DESCRIP-
TION section for the permissible combinations. If any operand is
specified as - (hyphen), standard input is read at that point.
If neither file1 nor file2 is a directory, then either can be given as -
(dash), in which case the standard input is used. If file1 is a directory
and file2 is a file, or vice versa, a file in the specified directory with
the same name as the specified file is used.
If both arguments are directories, diff sorts the contents of the direc-
tories by name, and then runs the regular diff file algorithm on text files
that are different. Binary files that differ, common subdirectories, and
files that appear in only one directory are also listed.
There are several choices for output format. The default output format
contains lines of these forms:
number1 a number2,number3
number1,number2 d number3
number1,number2 c number3,number4
These lines resemble ed commands to convert file1 into file2. In these
lines, the command a indicates that a line or lines were added to one of
the files; d indicates that a line or lines were deleted; and c indicates
that a line or lines were changed. The numbers after the letters pertain
to file2. In fact, by exchanging a for d and reading backward one can
ascertain equally how to convert file2 into file1. As in ed, identical
pairs where number1 = number2 or number3 = number4 are abbreviated as a
Following each of these lines come all the lines that are affected in the
first file, flagged by << (left angle bracket), then all the lines that are
affected in the second file, flagged by >> (right angle bracket).
Except in rare circumstances, diff finds the smallest sufficient set of
1. [Tru64 UNIX] Editing scripts produced by the -e or -f options cannot
create lines consisting of a single . (dot) character.
2. [Tru64 UNIX] Block, character, or FIFO special files cannot be used
with diff because they cause the command to exit.
3. [Tru64 UNIX] If lines at the end of a file are changed and other
lines added, diff output may show this as a delete and add, as a
change, or as a change and add. That is, diff is not expected to know
The following exit values are returned:
0 No differences.
1 Differences found.
>>1 An error occurred.
1. To compare two files, enter:
diff chap1.bak chap1
This displays the differences between the files chap1.bak and chap1.
2. To compare two files, ignoring differences in the amount of white
diff -b prog.c.bak prog.c
If two lines differ only in the number of spaces and tabs between
words, then the diff command considers them to be the same.
3. To create a file containing commands that the ed command can use to
reconstruct one file from another, enter:
diff -e ch2 ch2.old >> new.old.ed
This creates a file named new.to.old.ed that contains the ed subcom-
mands to change chap2 back into the version of the text found in
chap2.old. In most cases, new.to.old.ed is a much smaller file than
4. You can save disk space by deleting chap2.old, and you can reconstruct
it at any time by entering:
(cat new.old.ed ; echo '1,$p') | ed - ch2 >> ch2.old
The commands in parentheses add 1,$p to the end of the editing com-
mands sent to the ed editor. The 1,$p causes the ed command to write
the file to standard output after editing it. This modified command
sequence is then piped to the ed command ( | ed ), and the editor
reads it as standard input. The - option causes the ed command not to
display the file size and other extra information, since it would be
mixed with the text of chap2.old.
The following environment variables affect the execution of diff:
Provides a default value for the internationalization variables that
are unset or null. If LANG is unset or null, the corresponding value
from the default locale is used. If any of the internationalization
variables contain an invalid setting, the utility behaves as if none of
the variables had been defined.
If set to a non-empty string value, overrides the values of all the
other internationalization variables.
Determines the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to multi-
byte characters in arguments).
Determines the locale for the format and contents of diagnostic mes-
sages written to standard error.
Determines the location of message catalogues for the processing of
TZ Determines the locale for affecting the time zone used for calculating
the timestamps written with the -c and -C options.
For the -h option.
For the -l option.
Commands: bdiff(1), cmp(1), comm(1), diff3(1), ed(1), pr(1)