NAME

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 exclusive. 

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 combination with any others and in both file and directory comparisons. 

-bCauses trailing white space at the end of a line to be treated as a single newline character. 

-cProduces 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). 

-DstringCauses 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. 

-eProduces 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 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. 

-fProduces a script similar to that of -e, not useful with ed, and in the opposite order. 

-hPerforms a faster comparison.  This flag only works when the changed sections are short and well separated, but it does work on files of any length.  The -e and -f flags are not available when you use the -h flag. 

-iIgnores the case of letters.  For example, A is considered identical to a. 

-lSpecifies 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.  (Directory comparisons only.) 

-nProduces 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). 

-rChecks files in common subdirectories recursively. 

-sReports identical files, which are otherwise not mentioned. 

-SfileStarts a directory diff in the middle, beginning with file.  (Directory comparisons only.) 

-tExpands 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. 

-wIs 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 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 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 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. 

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 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 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/diffhFor the -h flag. 

/usr/bin/prFor the -l flag. 

NOTES

     1.Editing scripts produced by the -e or -f flags cannot create lines consisting of a single . (dot) character. 

     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).