(diffutils.info)Comparison

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1 What Comparison Means
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There are several ways to think about the differences between two files.
One way to think of the differences is as a series of lines that were
deleted from, inserted in, or changed in one file to produce the other
file.  'diff' compares two files line by line, finds groups of lines
that differ, and reports each group of differing lines.  It can report
the differing lines in several formats, which have different purposes.

   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.

   Another way to think of the differences between two files is as a
sequence of pairs of bytes that can be either identical or different.
'cmp' reports the differences between two files byte by byte, instead of
line by line.  As a result, it is often more useful than 'diff' for
comparing binary files.  For text files, 'cmp' is useful mainly when you
want to know only whether two files are identical, or whether one file
is a prefix of the other.

   To illustrate the effect that considering changes byte by byte can
have compared with considering them line by line, think of what happens
if a single newline character is added to the beginning of a file.  If
that file is then compared with an otherwise identical file that lacks
the newline at the beginning, 'diff' will report that a blank line has
been added to the file, while 'cmp' will report that almost every byte
of the two files differs.

   'diff3' normally compares three input files line by line, finds
groups of lines that differ, and reports each group of differing lines.
Its output is designed to make it easy to inspect two different sets of
changes to the same file.

   These commands compare input files without necessarily reading them.
For example, if 'diff' is asked simply to report whether two files
differ, and it discovers that the files have different sizes, it need
not read them to do its job.

Hunks

Groups of differing lines.

White Space

Suppressing differences in white space.

Blank Lines

Suppressing differences whose lines are all blank.

Specified Lines

Suppressing differences whose lines all match a pattern.

Case Folding

Suppressing differences in alphabetic case.

Brief

Summarizing which files are different.

Binary

Comparing binary files or forcing text comparisons.