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diff - differential file comparator

diff [-efbwr] file1... file2

Description

The diff command tells what lines must be changed in two files to bring them into agreement.

If one file is a directory	then a file in that directory with a basename the same as that of the other file is used
If both files are directories	similarly named files in the two directories are compared by the method of diff for text files and cmp otherwise
If more than two file names are given	then each argument is compared to the last argument as above

The normal output contains lines of these forms:

• n1 a n3, n4

• n1, n2 d n3

• n1, n2 c n3, n4

These lines resemble commands of the Unix system editor ed to convert file1 into file2. The numbers after the letters pertain to file2. In fact, by exchanging 'a' for 'd' and reading backward, it can be determined how to convert file2 into file1. As in ed, identical pairs where n1 = n2 or n3 = n4 are abbreviated as a single number.
Following each of these lines are the lines that are affected in the first file flagged by '<', then all the lines that are affected in the second file flagged by '>'.
Except in rare circumstances, diff finds a smallest sufficient set of file differences.

Options

-e	The -e option produces a script of a, c and d commands for the Unix system editor ed, which will recreate file2 from file1.
-f	The -f option produces a similar script, not useful with ed, in the opposite order. It may, however, be useful as input to a stream-oriented post-processor.
-b	The -b option causes trailing blanks (spaces and tabs) to be ignored and other strings of blanks to compare equal.
-w	The -w option causes all white space to be removed from input lines before applying the difference algorithm.
-r	The -r option causes diff to process similarly named subdirectories recursively.

Files

/tmp/diff[12]

Caveat

Editing scripts produced under the -e or -f option are naive about creating lines consisting of a single '.'. When running diff on directories, the notion of what is a text file is open to debate.

See Also

cmp - compare files

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