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 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 ( 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 byte 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 `-q' or
 `--brief' option for this.
 
    Differing binary files are considered to cause trouble because the
 resulting `diff' output does not capture all the differences.  This
 trouble causes `diff' to exit with status 2.  However, this trouble
 cannot occur with the `--a' or `--text' option, or with the `-q' or
 `--brief' option, as these options both cause `diff' to treat binary
 files like text files.
 
    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.
 
    The `--strip-trailing-cr' causes `diff' to treat input lines that
 end in carriage return followed by newline as if they end in plain
 newline.  This can be useful when comparing text that is imperfectly
 imported from many personal computer operating systems.  This option
 affects how lines are read, which in turn affects how they are compared
 and output.
 
    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 `-b' option to
 show the ASCII representation of those bytes.   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 bytes 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.
 

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