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diff

Display the differences between two files, or each corresponding file in two directories.
Each set of differences is called a "diff" or "patch". For files that are identical, `diff' normally produces no output; for binary (non-text) files, `diff' normally reports only that they are different.

SYNTAX
      diff [options] from-file to-file
OPTIONS
   Multiple single letter options (unless they take an argument) can be combined into a single command 
line word: so `-ac' is equivalent to `-a -c'.
-lines Show lines lines of context. This option is obsolete. -a Treat all files as text and compare them line-by- line, even if they do not seem to be text. -b Ignore changes in amount of white space. -B Ignore changes that just insert or delete blank lines. --brief Report only whether the files differ, not the details of the differences. -c Use the context output format. -C lines --context[=lines] Use the context output format, showing lines (an integer) lines of context, or three if lines is not given. For proper operation, patch typically needs at least two lines of context. --changed-group-format=format Use format to output a line group containing dif- fering lines from both files in if-then-else for- mat. -d Change the algorithm to perhaps find a smaller set of changes. This makes diff slower (sometimes much slower). -D name Make merged if-then-else format output, conditional on the preprocessor macro name. -e --ed Make output that is a valid ed script. --exclude=pattern When comparing directories, ignore files and subdi- rectories whose basenames match pattern. --exclude-from=file When comparing directories, ignore files and subdi- rectories whose basenames match any pattern con- tained in file. --expand-tabs Expand tabs to spaces in the output, to preserve the alignment of tabs in the input files. -f Make output that looks vaguely like an ed script but has changes in the order they appear in the file. -F regexp In context and unified format, for each hunk of differences, show some of the last preceding line that matches regexp. --forward-ed Make output that looks vaguely like an ed script but has changes in the order they appear in the file. -h This option currently has no effect; it is present for Unix compatibility. -H Use heuristics to speed handling of large files that have numerous scattered small changes. --horizon-lines=lines Do not discard the last lines lines of the common prefix and the first lines lines of the common suf- fix. -i Ignore changes in case; consider upper- and lower- case letters equivalent. -I regexp Ignore changes that just insert or delete lines that match regexp. --ifdef=name Make merged if-then-else format output, conditional on the preprocessor macro name. --ignore-all-space Ignore white space when comparing lines. --ignore-blank-lines Ignore changes that just insert or delete blank lines. --ignore-case Ignore changes in case; consider upper- and lower- case to be the same. --ignore-matching-lines=regexp Ignore changes that just insert or delete lines that match regexp. --ignore-space-change Ignore changes in amount of white space. --initial-tab Output 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. -l Pass the output through pr to paginate it. -L label --label=label Use label instead of the file name in the context format and unified format headers. --left-column Print only the left column of two common lines in side by side format. --line-format=format Use format to output all input lines in in-then- else format. --minimal Change the algorithm to perhaps find a smaller set of changes. This makes diff slower (sometimes much slower). -n Output RCS-format diffs; like -f except that each command specifies the number of lines affected. -N --new-file In directory comparison, if a file is found in only one directory, treat it as present but empty in the other directory. --new-group-format=format Use format to output a group of lines taken from just the second file in if-then-else format. --new-line-format=format Use format to output a line taken from just the second file in if-then-else format. --old-group-format=format Use format to output a group of lines taken from just the first file in if-then-else format. --old-line-format=format Use format to output a line taken from just the first file in if-then-else format. -p Show which C function each change is in. -P When comparing directories, if a file appears only in the second directory of the two, treat it as present but empty in the other. --paginate Pass the output through pr to paginate it. -q Report only whether the files differ, not the details of the differences. -r When comparing directories, recursively compare any subdirectories found. --rcs Output RCS-format diffs; like -f except that each command specifies the number of lines affected. --recursive When comparing directories, recursively compare any subdirectories found. --report-identical-files -s Report when two files are the same. -S file When comparing directories, start with the file file. This is used for resuming an aborted compar- ison. --sdiff-merge-assist Print extra information to help sdiff. sdiff uses this option when it runs diff. This option is not intended for users to use directly. --show-c-function Show which C function each change is in. --show-function-line=regexp In context and unified format, for each hunk of differences, show some of the last preceding line that matches regexp. --side-by-side Use the side by side output format. --speed-large-files Use heuristics to speed handling of large files that have numerous scattered small changes. --starting-file=file When comparing directories, start with the file file. This is used for resuming an aborted compar- ison. --suppress-common-lines Do not print common lines in side by side format. -t Expand tabs to spaces in the output, to preserve the alignment of tabs in the input files. -T Output 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. --text Treat all files as text and compare them line-by- line, even if they do not appear to be text. -u Use the unified output format. --unchanged-group-format=format Use format to output a group of common lines taken from both files in if-then-else format. --unchanged-line-format=format Use format to output a line common to both files in if-then-else format. --unidirectional-new-file When comparing directories, if a file appears only in the second directory of the two, treat it as present but empty in the other. -U lines --unified[=lines] Use the unified output format, showing lines (an integer) lines of context, or three if lines is not given. For proper operation, patch typically needs at least two lines of context. -v --version Output the version number of diff. -w Ignore white space when comparing lines. -W columns --width=columns Use an output width of columns in side by side for- mat. -x pattern When comparing directories, ignore files and subdi- rectories whose basenames match pattern. -X file When comparing directories, ignore files and subdi- rectories whose basenames match any pattern con- tained in file. -y Use the side by side output format.

In the simplest case, diff compares the contents of the two files from-file and to-file. A file name of - stands for text read from the standard input.

If from-file is a directory and to-file is not, diff compares the file in from-file whose file name is that of to-file, and vice versa. The non-directory file must not be -.

If both from-file and to-file are directories, diff compares corresponding files in both directories, in alphabetical order; this comparison is not recursive unless the -r or --recursive option is given.

GNU `diff' can show whether files are different without detailing the differences.
It also provides ways to suppress certain kinds of differences that are not important to you.

Most commonly, such differences are changes in the amount of white space between words or lines. `diff' also provides ways to suppress differences in alphabetic case or in lines that match a regular expression that you provide.

These options can accumulate; for example, you can ignore changes in both white space and alphabetic case.

End -of-Line markers

In operating systems that distinguish between text and binary files, `diff' normally reads and writes all data as text.

Use the `--binary' option to force `diff' to read and write binary data instead. This option has no effect on a Posix-compliant system like GNU or traditional Unix. However, many personal computer operating systems represent the end of a line with a carriage return followed by a newline.

On such systems, `diff' normally ignores these carriage returns on input and generates them at the end of each output line, but with the `--binary' option `diff' treats each carriage return as just another input character, and does not generate a carriage return at the end of each output line.

This can be useful when dealing with non-text files that are meant to be interchanged with Posix-compliant systems.

Suppressing Differences in Blank and Tab Spacing

The `-b' and `--ignore-space-change' options ignore white space at line end, and considers all other sequences of one or more white space characters to be equivalent.
With these options, `diff' considers the following two lines to be equivalent, where `$' denotes the line end:

Here lyeth muche rychnesse in lytell space. -- John Heywood$
Here lyeth muche rychnesse in lytell space. -- John Heywood $

The `-w' and `--ignore-all-space' options are stronger than `-b'. They ignore difference even if one file has white space where the other file has none. "White space" characters include tab, newline, vertical tab, form feed, carriage return, and space; some locales may define additional characters to be white space.
With these options, `diff' considers the following two lines to be equivalent, where `$' denotes the line end and `^M' denotes a carriage return:

Here lyeth muche rychnesse in lytell space.-- John Heywood$
He relyeth much erychnes seinly tells pace. --John Heywood

GNU `diff' can treat lowercase letters as equivalent to their uppercase counterparts, so that, for example, it considers `Funky Stuff', `funky STUFF', and `fUNKy stuFf' to all be the same.
To request this, use the `-i' or `--ignore-case' option.

Suppressing Lines Matching a Regular Expression
To ignore insertions and deletions of lines that match a regular expression, use the `-I REGEXP' or `--ignore-matching-lines=REGEXP' option.
You should escape regular expressions that contain shell metacharacters to prevent the shell from expanding them.

For example, `diff -I '^[0-9]'' ignores all changes to lines beginning with a digit.

However, `-I' only ignores the insertion or deletion of lines that contain the regular expression if every changed line in the hunk--every insertion and every deletion--matches the regular expression.

In other words, for each nonignorable change, `diff' prints the complete set of changes in its vicinity, including the ignorable ones. You can specify more than one regular expression for lines to ignore by using more than one `-I' option. `diff' tries to match each line against each regular expression, starting with the last one given.

Summarizing Which Files Differ
When you only want to find out whether files are different, and you don't care what the differences are, you can use the summary output format.
In this format, instead of showing the differences between the files, `diff' simply reports whether files differ.
The `-q' and `--brief' options select this output format.
This format is especially useful when comparing the contents of two directories. It is also much faster than doing the normal line by line comparisons, because `diff' can stop analyzing the files as soon as it knows that there are any differences.
You can also get a brief indication of whether two files differ by using `cmp'.

Using diff to patch a file
To show context around the differing lines GNU `diff' provides these output formats

Normal Format: An output format that shows each hunk of differences without any surrounding context
Context Format:: An output format that shows surrounding lines.
Unified Format:: A more compact output format that shows context.

`patch' can apply diffs by searching in the files for the lines of context around the differing lines; if those lines are actually a few lines away from where the diff says they are, `patch' can adjust the line numbers accordingly and still apply the diff correctly.

For more on patching files and producing commands that direct the `ed' text editor to edit a file - see `info diff'

# Oh lord won't you buy me a Mercedes Benz, my friends all drive Porsches, I must make amends # - Janice Joplin

Related commands:

cmp - Compare two files
dircmp - Compare 2 directories
diff3 - Show differences among three files
sdiff - Merge two files interactively