# ifdef(1)

    NAME
         ifdef - remove #ifdefs from a file

    SYNOPSIS
         ifdef [-t] [-dsymbol] [-Dsymbol] [-Usymbol] [-Isymbol] [file]

    OPTIONS

         -D   Define symbol permanently

         -I   Ignore symbol

         -U   Undefine symbol permanently

         -d   Define symbol. It may be #undef'ed later

         -t   Produce a table of the symbols on stdout

    EXAMPLES

         ifdef -DUNIX file.c >newfile.c
                             # Define UNIX

         ifdef -D_MINIX -UDOS <x.c >y.c
                             # Define

    DESCRIPTION

         Ifdef allows conditional code [ #ifdef ... #endif  ]  to  be  selectively
         removed  from  C  files,  but  at  the  same  time  leaving  all  other C
         preprocessor commands intact such as #define,  #include  etc.   Input  to
         ifdef  is either the file named as the last argument, or stdin if no file
         is named.  Output goes to stdout.

         Symbols may be defined with the -d or -D flags just like cpp, except that
         the  latter  option  ignores  subsequent #undefs.  It is not permitted to
         give values to symbols.  Similarly, -U undefines  a  symbol  and  ignores
         subsequent  #definess.   Symbols  defined with -I are ignored; any #ifdef
         using an ignored symbol will be left intact.