Compare Files or Directories
Usage: diff [-bBeEfhiNqrsvw!-] [-m minmatch] [-n maxbest] [-o maxwindow]
[-Dstring] [-dstring] oldpath newpath
diff produces a list of differences between two files or
directories. The working assumption is that newpath is a
newer version of whatever's in oldpath. If they're files,
diff assumes they contain ascii text but if it encounters a
file containing lots of binary data, it switches to a binary
comparison mode to avoid dumping gibberish to the screen.
Comparing files, diff looks for minimal sections of change.
Each difference is shown as an add, delete or change with the
appropriate line numbers or line number ranges for each file.
Following are texts of the differing section. Lines that have
been deleted are flagged with '<'; lines that have been added
are flagged with '>'. Alternately, diff can be used to produce
merged listings with #ifdefs for the C compiler or highlighting
for quick visual scanning.
The algorithm for comparing files is to maintain sliding
windows into each of the two files, adding new lines to each
window until there is a matching sequence of some minimal
number of lines at the bottom of each window. That minimum
can be configured via the -m option.
Once that minimal match is found, diff begins to compare the
two windows in an attempt to minimize the number of lines in
each that cannot be matched against the other. If the combined
total number of lines in the two windows is less than some
heuristic limit, set via the -n option, diff will do this
comparison with a recursive algorithm guaranteed to find the
absolute best solution. But because the computation involved
in this approach grows very quickly as the number of lines
increases, diff switches to a heuristic approach for more
complex window comparisons, breaking the windows down into
smaller segments against which the exhaustive approach can
be used.
Comparing directories, diff builds lists of all the files
they contain, searching all the way down through the tree.
The lists are sorted, then compared. If the same filename
exists in each directory tree, a quick binary comparison is
normally made of whether they contain the same or different
data. If -r is specified, the diff text comparison is done
recursively the whole way down the two trees.
If one of the arguments to diff is a file and the other is a
directory, diff will look for and compare against a file of
that same name in the directory.
Options:
-b Blank spaces of any length compare equal. Ignore
any leading or trailing white space on each line.
-B Binary comparison even on text files.
-Dstring Produce a merged #ifdef'ed listing, with the string
being defined meaning use the older version. (Newer
version is intentionally the default.)
-dstring Same as -Dstring, but add comments of the form
/* string */ to the #else and #endif directives
that are generated.
-e Produce an ed script which, when a w (the write
command) is appended to it, can be used to
transform the first file into the second.
-E Turn off highlighting of empty lines. By default,
if highlighting is used to show areas of change,
even empty lines will have ANSI sequences at the
beginning and end so that if more is used to display
the output with the default color stretch mode on,
empty lines will still be highlighted.
-f Force diff-style comparison to continue even on files
that appear to contain binary data.
-h Help. (This screen.)
-i Ignore character case.
-m minmatch Minimum match length to insist on before resynchro-
nizing two files. (Default is 20 lines.)
-n maxbest Maximum total number of lines in the two windows
against which diff will attempt an absolute best
match. If the total is larger, it will attempt
to break the problem down with heuristics.
(Default is 15 lines.)
-N Ignore differences in line endings. NewLine and
CarriageReturn-NewLine endings will be considered
equal.
-o maxwindow Maximum total number of lines that diff will
allow to be collected into the two windows before
it gives up looking for a resynchronizing match.
(Default is 4000 lines.)
-q Quiet: suppress warnings about files containing
binary data.
-r Recursively diff the contents of any subdirectories.
-s Add spaces to separate the a (add), c (change) or d
(delete) characters from the line numbers in a diff
report for better readability.
-v Verbose listing of all the contents of any entire
subdirectory added or deleted.
-w White space is ignored totally.
-! Produce merged, highlighted version. Text that's
unchanged is normal, deleted text is red, new text
is green.
-- End of options.
Colors:
You may set your own choices for screen colors using these
environmental variables:
Name Use Default
COLORS Normal screen colors <null string>
ADDITIONS Lines added Bright White on Green
DELETIONS Lines deleted Bright White on Red
Colors recognized are black, red, green, yellow, blue, magenta
(or red blue), cyan (or blue green) or white. Foreground and
background colors may also be bright, dim or reverse. The names
of the colors and the words bright, dim, reverse and on may be
in either upper or lower or mixed case.
Either or both the foreground and background colors may be
specified; if you don't specify a value, it's considered
transparent and inherits the color underneath it. ADDITIONS
and DELETIONS inherit from COLORS. If COLORS is null, diff
uses the current screen colors it finds at startup.
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