Editing Diff (section)

== Usage ==
The <code>diff</code> command is invoked from the command line, passing it the names of two files: <code>diff ''original'' ''new''</code>. The output of the command represents the changes required to transform the ''original'' file into the ''new'' file.

If ''original'' and ''new'' are directories, then {{Mono|diff}} will be run on each file that exists in both directories. An option, <code>-r</code>, will recursively descend any matching subdirectories to compare files between directories.

Any of the examples in the article use the following two files, ''original'' and ''new'':
{{Col-begin}}
{{Col-break|width=33%}}
''original'':
<syntaxhighlight lang="text" line>
This part of the
document has stayed the
same from version to
version.  It shouldn't
be shown if it doesn't
change.  Otherwise, that
would not be helping to
compress the size of the
changes.

This paragraph contains
text that is outdated.
It will be deleted in the
near future.

It is important to spell
check this dokument. On
the other hand, a
misspelled word isn't
the end of the world.
Nothing in the rest of
this paragraph needs to
be changed. Things can
be added after it.
</syntaxhighlight>
{{col-break}}
''new'':
<syntaxhighlight lang="text" line>
This is an important
notice! It should
therefore be located at
the beginning of this
document!

This part of the
document has stayed the
same from version to
version.  It shouldn't
be shown if it doesn't
change.  Otherwise, that
would not be helping to
compress the size of the
changes.

It is important to spell
check this document. On
the other hand, a
misspelled word isn't
the end of the world.
Nothing in the rest of
this paragraph needs to
be changed. Things can
be added after it.

This paragraph contains
important new additions
to this document.
</syntaxhighlight>
{{col-break|width=33%}}
The command '''<code>diff original new</code>''' produces the following ''normal diff output'':
{{pre|
0a1,6
{{font color|darkgreen|> This is an important
> notice! It should
> therefore be located at
> the beginning of this
> document!
>}}
11,15d16
{{font color|darkred|< This paragraph contains
< text that is outdated.
< It will be deleted in the
< near future.
<}}
17c18
{{font color|darkred|< check this dokument. On}}
---
{{font color|darkgreen|> check this document. On}}
24a26,29
{{font color|darkgreen|>
> This paragraph contains
> important new additions
> to this document.}}}}

'''Note''': ''Here, the diff output is shown with colors to make it easier to read. The diff utility does not produce colored output; its output is [[plain text]]. However, many tools can show the output with colors by using [[syntax highlighting]].''
{{col-end}}
In this traditional output format, '''<samp>a</samp>''' stands for ''added'', '''<samp>d</samp>''' for ''deleted'' and '''<samp>c</samp>''' for ''changed''. Line numbers of the original file appear before <samp>a</samp>/<samp>d</samp>/<samp>c</samp> and those of the new file appear after. The [[Less-than sign|less-than]] and [[Greater-than sign|greater-than]] signs (at the beginning of lines that are added, deleted or changed) indicate which file the lines appear in. Addition lines are added to the original file to appear in the new file. Deletion lines are deleted from the original file to be missing in the new file.

By default, lines common to both files are not shown. Lines that have moved are shown as added at their new location and as deleted from their old location.<ref>{{cite book|title=Comparing and Merging Files with GNU Diff and Patch|url=https://www.gnu.org/software/diffutils/manual/|author1=David MacKenzie|author2=Paul Eggert|author3=Richard Stallman|isbn=978-0-9541617-5-0|publisher=Network Theory|year=1997|location=Bristol|access-date=2015-03-17|archive-date=2015-03-31|archive-url=https://web.archive.org/web/20150331031946/http://www.gnu.org/software/diffutils/manual/|url-status=live}}</ref> However, some diff tools highlight moved lines.