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diff - display line-by-line differences between pairs of text files
diff [ -# ] [ -abBcdefhHilnNprstTuvw ] [ -C lines ] [ -F regexp ] [ -I regexp ] [ -L label [ -L label ] ] [ -S file ] [ -D symbol ] path1 path2
diff is a differential file comparator. The GNU version provides all the features of BSD's diff with some additional features added. When run on regular files, and when comparing text files that differ during directory comparison (see the notes below on comparing directories), 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 differences. If neither filename1 nor filename2 is a directory, either may be given as `-', in which case the standard input is used. If filename1 is a directory, a file in that directory whose filename is the same as the filename of filename2 is used (and vice versa). 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 ed(1) commands to convert filename1 into filename2. The numbers after the letters pertain to filename2. In fact, by exchanging a for d and reading backward one may ascertain equally how to convert filename2 into filename1. As in ed(1), 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 `>'. If both arguments are directories, diff sorts the contents of the directories by name, and then runs the regular file diff program as described above on text files which are different. Binary files which differ, common subdirectories, and files which appear in only one directory are listed. GNU diff has these additional features: An input file may end in a non-newline character. If so, its last line is called an incomplete line and is distinguished on output from a full line. In the default, -c, and -u output styles, an incomplete output line is followed by a diagnostic line that starts with `\'. With -n, an incomplete line is output without a trailing newline. Other output styles (-D, -e, -f) cannot represent an incomplete line, so they pretend that there was a newline, and -e and -f also print an error message. For example, suppose F and G are one-byte files that contain just ``f'' and ``g'', respectively. Then ``diff F G'' outputs: 1c1 < f \ No newline at end of file --- > g \ No newline at end of file (The exact diagnostic message may differ, e.g. for non- English locales.) ``diff -n F G'' outputs the following without a trailing newline: d1 1 a1 1 g ``diff -e F G'' sends two diagnostics to stderr and the following to stdout: 1c g A file is considered to be text if its first characters are all in the ISO 8859 character set; BSD's diff uses Ascii.
-b Ignore trailing blanks (SPACE and TAB characters) and treat all other strings of blanks as equivalent. -i Ignore the case of letters; for example, `A' will compare equal to `a'. -t Expand TAB characters in output lines. Normal or -c output adds character(s) to the front of each line which may alter the indentation of the original source lines and make the output listing difficult to interpret. This option will preserve the original source's indentation. -w Ignore all blanks (SPACE and TAB characters); for example, `if ( a == b )' will compare equal to `if(a==b)'. The following four options are mutually exclusive: -c Produce a listing of differences with lines of context. -e Produce a script of a, c, and d commands for the editor ed, which will recreate filename2 from filename1. 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. 9 (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 script for converting text files which are common to the two directories from their state in directory1 to their state in directory2. -f Produce a script similar to that of -e, not useful with ed, which is in the opposite order. -n Produce 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. -h Do a fast, half-hearted job. It works only when changed stretches are short and well separated, but does work on files of unlimited length. Options for the second form of diff are as follows: -D symbol Create a merged version of filename1 and filename2 on the standard output, with C preprocessor controls included so that a compilation of the result without defining string is equivalent to compiling filename1, while defining string will yield filename2. Options when comparing directories are: -l Long output format; each text file diff is piped through pr(1V) to paginate it, other differences are remembered and summarized after all text file differences are reported. -r Apply diff recursively to common subdirectories encountered. -s Report files which are the same, which are otherwise not mentioned. Start a directory diff in the middle, beginning with file name. GNU DIFF has the following additional options: -a Always treat files as text and compare them line-by- line, even if they do not appear to be text. -B Ignore changes that just insert or delete blank lines. -C [#] Request the -c format and specify the number of context lines. -F regexp In context format, for each unit of differences, show some of the last preceding line that matches the specified regexp. -H Use heuristics to speed handling of large files that have numerous scattered small changes. The algorithm becomes asymptotically linear for such files! -I regexp Ignore changes that just insert or delete lines that match the specified regexp. -L label Use the specified label in file header lines output by the -c option. This option may be given zero, one, or two times, to affect neither label, just the first file's label, or both labels. A file's default label is its name, a tab, and its modification date. -N In directory comparison, if a file is found in only one directory, treat it as present but empty in the other directory. -T Print a tab rather than a space before the text of a line in normal or context format. This causes the alignment of tabs in the line to look normal. -u[#] Produce unified style output with # context lines (default 3). This style is like -c , but it is more compact because context lines are printed only once. Lines from just the first file are marked '-'; lines from just the second file are marked '+'.
cc(1V), cmp(1), comm(1), cpp(1), diff3(1V), ed(1), pr(1V), locale(5), iso_8859_1(7)
Exit status is 0 for no differences, 1 for some differences, 2 for trouble.
Editing scripts produced under the -e or -f option are naive about creating lines consisting of a single `.'. When comparing directories with the -b, -w, or -i options specified, diff first compares the files (as in cmp(1), and then runs the regular 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 or case differences. The -D option ignores existing preprocessor controls in the source files, and can generate #ifdefs's with overlapping scope. The output should be checked by hand, or run through `cc -E' (see cc(1V)) and then diffed with the original source files. Discrepancies revealed should be corrected before compilation.
GNU DIFF was written by Mike Haertel, David Hayes, Richard Stallman and Len Tower. The basic algorithm is described in: "An O(ND) Difference Algorithm and its Variations", Eugene Myers, Algorithmica Vol. 1 No. 2, 1986, p 251. Many bugs were fixed by Paul Eggert. The unified diff idea and format are from Wayne Davison.