Info Catalog diffutils: Example If-then-else diffutils: If-then-else

diffutils: Detailed If-then-else

 
 2.6.4 Detailed Description of If-then-else Format
 -------------------------------------------------
 
 For lines common to both files, 'diff' uses the unchanged line group
 format.  For each hunk of differences in the merged output format, if
 the hunk contains only lines from the first file, 'diff' uses the old
 line group format; if the hunk contains only lines from the second file,
 'diff' uses the new group format; otherwise, 'diff' uses the changed
 group format.
 
    The old, new, and unchanged line formats specify the output format of
 lines from the first file, lines from the second file, and lines common
 to both files, respectively.
 
    The option '--ifdef=NAME' is equivalent to the following sequence of
 options using shell syntax:
 
      --old-group-format='#ifndef NAME
      %<#endif /* ! NAME */
      ' \
      --new-group-format='#ifdef NAME
      %>#endif /* NAME */
      ' \
      --unchanged-group-format='%=' \
      --changed-group-format='#ifndef NAME
      %<#else /* NAME */
      %>#endif /* NAME */
      '
 
    You should carefully check the 'diff' output for proper nesting.  For
 example, when using the '-D NAME' or '--ifdef=NAME' option, you should
 check that if the differing lines contain any of the C preprocessor
 directives '#ifdef', '#ifndef', '#else', '#elif', or '#endif', they are
 nested properly and match.  If they don't, you must make corrections
 manually.  It is a good idea to carefully check the resulting code
 anyway to make sure that it really does what you want it to; depending
 on how the input files were produced, the output might contain duplicate
 or otherwise incorrect code.
 
    The 'patch' '-D NAME' option behaves like the 'diff' '-D NAME'
 option, except it operates on a file and a diff to produce a merged
 file.  ⇒patch Options.
 

Info Catalog diffutils: Example If-then-else diffutils: If-then-else