GNU Info

(diff.info)Binary

---

Prev: Brief Up: Comparison

---

Enter node , (file) or (file)node

Binary Files and Forcing Text Comparisons
=========================================

   If `diff' thinks that either of the two files it is comparing is
binary (a non-text file), it normally treats that pair of files much as
if the summary output format had been selected (Note: Brief), and
reports only that the binary files are different.  This is because line
by line comparisons are usually not meaningful for binary files.

   `diff' determines whether a file is text or binary by checking the
first few bytes in the file; the exact number of bytes is system
dependent, but it is typically several thousand.  If every character in
that part of the file is non-null, `diff' considers the file to be
text; otherwise it considers the file to be binary.

   Sometimes you might want to force `diff' to consider files to be
text.  For example, you might be comparing text files that contain null
characters; `diff' would erroneously decide that those are non-text
files.  Or you might be comparing documents that are in a format used
by a word processing system that uses null characters to indicate
special formatting.  You can force `diff' to consider all files to be
text files, and compare them line by line, by using the `-a' or
`--text' option.  If the files you compare using this option do not in
fact contain text, they will probably contain few newline characters,
and the `diff' output will consist of hunks showing differences between
long lines of whatever characters the files contain.

   You can also force `diff' to consider all files to be binary files,
and report only whether they differ (but not how).  Use the `--brief'
option for this.

   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.

   If you want to compare two files byte by byte, you can use the `cmp'
program with the `-l' option to show the values of each differing byte
in the two files.  With GNU `cmp', you can also use the `-c' option to
show the ASCII representation of those bytes.  Note: Invoking cmp,
for more information.

   If `diff3' thinks that any of the files it is comparing is binary (a
non-text file), it normally reports an error, because such comparisons
are usually not useful.  `diff3' uses the same test as `diff' to decide
whether a file is binary.  As with `diff', if the input files contain a
few non-text characters but otherwise are like text files, you can
force `diff3' to consider all files to be text files and compare them
line by line by using the `-a' or `--text' options.