diff -- Command

Compare two files
diff [-bdefh] [-c symbol] file1 file2

diff compares file1 with file2, and  prints a summary of the changes needed
to turn file1 into file2.

Two options  involve input file  specification.  First, the  standard input
may be  specified in place of  a file by entering a hyphen  `-' in place of
file1 or  file2. Second, if  file1 is a  directory, diff looks  within that
directory for a  file that has the same name  as file2, then compares file2
with the file of the same name in directory file1.

The default output script has lines in the following format:

    1,2 c 3,4

The numbers 1,2 refer to line  ranges in file1, and 3,4 to ranges in file2.
The range is abbreviated to a single number if the first number is the same
as the  second.  The command c  was chosen from among  the ed commands `a',
`c', and `d'.  diff then prints  the text from each of the two files.  Text
associated with file1 is preceded by `< ', whereas  text associated with
file2 is preceded by `>'.

The following summarizes diff's options.

-b Ignore trailing blanks and treat more than one blank in an input line as
   a single  blank.  Spaces and tabs  are considered to be  blanks for this
   comparison.

-c symbol
   Produce output suitable for  the C preprocessor cpp; the output contains
   #ifdef, #ifndef, #else,  and #endif lines.  symbol is the string used to
   build the #ifdef statements.  If you define symbol to the C preprocessor
   cpp, it  will produce  file2 as its  output; otherwise, it  will produce
   file1. This option does not  work for files that already contain #ifdef,
   #ifndef, #else, and #endif statements.

-e Create an ed script that will convert file1 into file2.

-f Produce a  script in  the same  manner as the  -e option, but  with line
   numbers  taken  directly  from the  two  input  files.   This will  work
   properly  only if  applied  from end  to  beginning; it  cannot be  used
   directly by ed.

-h Compare large  files that  have a  minimal number of  differences.  This
   option uses an algorithm that is not limited by file length, but may not
   discover all differences.

-d Select  the  -h  algorithm only  for  files  larger  than 25,000  bytes;
   otherwise, use the normal algorithm.

Example

For an  example of a script  that uses this command,  see the Lexicon entry
for trap.

See Also

ed,
egrep,
commands,
zdiff

Diagnostics

diff's exit status is zero when  the files are identical, one when they are
different, and  two if a  problem was encountered  (e.g., could not  open a
file).

Notes

diff cannot handle files with more  than 32,000 lines.  Handing diff a file
that  exceeds that  limit will  cause it to  fail, with  unpredictable side
effects.

© 2012 by Stephen A. Ness