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(diff.info)Comparison

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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 characters that can be either identical or
different.  `cmp' reports the differences between two files character
by character, instead of line by line.  As a result, it is 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.

   To illustrate the effect that considering changes character by
character 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 character 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.

Hunks

Groups of differing lines.

White Space

Suppressing differences in white space.

Blank Lines

Suppressing differences in blank lines.

Case Folding

Suppressing differences in alphabetic case.

Specified Folding

Suppressing differences that match regular expressions.

Brief

Summarizing which files are different.

Binary

Comparing binary files or forcing text comparisons.