diff(1) General Commands Manual diff(1)
diff - Compares text files
diff [-c | -C number | -e | -f | -h | -n] [-bilrstw] [-Sfile] directory1 directory2
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 as follows:
Refer to the standards(5) reference page for more information about industry 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 only.
The -b, -i, -l, -t, and -w options can be used in combination with any others and in both file and directory comparisons. Causes trailing
white space at the end of a line to be treated as a single newline character. Produces a listing with the default number of lines of con-
text (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 num-
ber of lines of each other are grouped together on output. Produces output that provides number lines of context (where number is a posi-
tive 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 compiling file1, while defining string
yields file2. 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. Produces a script similar to that
of -e, not useful with ed, and in the opposite order. [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. [Tru64 UNIX] Ignores the case of letters. For example, A is considered identical to a. [Tru64
UNIX] Specifies long output format; each text file diff listing is piped through pr to paginate it, other differences are remem-
bered and summarized after all text file differences are reported. (Directory comparisons only.) [Tru64 UNIX] 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 the revision control system (RCS). Checks files in common subdirectories recursively. [Tru64 UNIX] Reports identical
files, which are otherwise not mentioned. [Tru64 UNIX] Starts a directory diff in the middle, beginning with file. (Directory
comparisons only.) [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. [Tru64 UNIX] Is similar to -b, but causes whitespace (spaces and tabs) to be ignored. For
example, if ( a == b ) is considered identical to if(a==b).
The path names of files or directories to be compared. See the DESCRIPTION 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 directories 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
There are several choices for output format. The default output format contains lines of these forms: number1 a number2,number3 num-
ber1,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 single number.
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 file differences.
[Tru64 UNIX] Editing scripts produced by the -e or -f options cannot create lines consisting of a single . (dot) character. [Tru64
UNIX] Block, character, or FIFO special files cannot be used with diff because they cause the command to exit. [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 what happened.
The following exit values are returned: No differences. Differences found. An error occurred.
To compare two files, enter: diff chap1.bak chap1
This displays the differences between the files chap1.bak and chap1. To compare two files, ignoring differences in the amount of
white space, enter: 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. To
create a file containing commands that the ed command can use to reconstruct one file from another, enter: diff -e ch2 ch2.old >
This creates a file named new.to.old.ed that contains the ed subcommands 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 chap2.old. 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,$p to the end of the editing commands sent to the ed editor. The 1,$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 vari-
ables 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 multibyte characters in arguments). Determines the locale for the for-
mat and contents of diagnostic messages written to standard error. Determines the location of message catalogues for the processing of
LC_MESSAGES. 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)