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Man Page for DIFFNAME
diff - Compares text files
SYNOPSIS
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
FLAGS
The -c, -C, -e, -f, -h, and -n flags are mutually exclu-
sive.
The -r, -s, and -S flags can be specified with directory
comparisons only.
The -b, -i, -l, -t, and -w flags can be used in combina-
tion with any others and in both file and directory com-
parisons.
-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.
-C number
Produces output that provides number lines of context
(where number is a positive decimal integer).
-Dstring
Causes diff to create a merged version of file1 and
file2 on the standard output, with C preprocessor con-
trols included. Thus, a compilation of the result
without defining string is equivalent to compiling
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
Extra commands are added to the output when compar-
ing 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 opposite order.
-h Performs a faster comparison. This flag only works
when the changed sections are short and well sepa-
rated, but it does work on files of any length. The
-e and -f flags are not available when you use the -h
flag.
-i Ignores the case of letters. For example, A is con-
sidered identical to a.
-l Specifies long output format; each text file diff
listing is piped through pr to paginate it, other dif-
ferences are remembered and summarized after all text
file differences are reported. (Directory comparisons
only.)
-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 the revision control system (RCS).
-r Checks files in common subdirectories recursively.
-s Reports identical files, which are otherwise not men-
tioned.
-Sfile
Starts a directory diff in the middle, beginning with
file. (Directory comparisons only.)
-t 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 flag preserves the original source's indentation.
-w 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).
DESCRIPTION
Input Options
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 spec-
ified 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 listed.
Output Options
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. 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 let-
ters 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 small-
est sufficient set of file differences.
EXAMPLES
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 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 con-
siders them to be the same.
3. To create a file containing commands that the ed com-
mand 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 con-
tains 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.
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,$p to the end of
the editing commands sent to the ed editor. The
1,$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 - flag 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.
FILES
/usr/lbin/diffh
For the -h flag.
/usr/bin/pr
For the -l flag.
NOTES
1. Editing scripts produced by the -e or -f flags cannot
create lines consisting of a single . (dot) charac-
ter.
2. Block, character, or FIFO special files cannot be
used with diff because they cause the command to
exit.
3. 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.
EXIT VALUES
An exit value of 0 (zero) indicates no differences, 1
indicates differences found, and a number greater than 1
indicates an error.
RELATED INFORMATION
Commands: bdiff(1), cmp(1), comm(1), diff3(1),
ed(1)/red(1), pr(1). delim off
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