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UNIFDEF(1)                BSD General Commands Manual               UNIFDEF(1)

     unifdef, unifdefall -- remove preprocessor conditionals from code

     unifdef [-ceklst] [-Ipath] [-Dsym[=val]] [-Usym] [-iDsym[=val]] [-iUsym]
             ... [-o output] [file]
     unifdefall [-Ipath] ... file

     The unifdef utility selectively processes conditional cpp(1) directives.
     It removes from a file both the directives and any additional text that
     they specify should be removed, while otherwise leaving the file alone.

     The unifdef utility acts on #if, #ifdef, #ifndef, #elif, #else, and
     #endif lines, and it understands only the commonly-used subset of the
     expression syntax for #if and #elif lines.  It handles integer values of
     symbols defined on the command line, the defined() operator applied to
     symbols defined or undefined on the command line, the operators !, <, >,
     <=, >=, ==, !=, &&, ||, and parenthesized expressions.  Anything that it
     does not understand is passed through unharmed.  It only processes #ifdef
     and #ifndef directives if the symbol is specified on the command line,
     otherwise they are also passed through unchanged.  By default, it ignores
     #if and #elif lines with constant expressions, or they may be processed
     by specifying the -k flag on the command line.

     The unifdef utility also understands just enough about C to know when one
     of the directives is inactive because it is inside a comment, or affected
     by a backslash-continued line.  It spots unusually-formatted preprocessor
     directives and knows when the layout is too odd to handle.

     A script called unifdefall can be used to remove all conditional cpp(1)
     directives from a file.  It uses unifdef -s and cpp -dM to get lists of
     all the controlling symbols and their definitions (or lack thereof), then
     invokes unifdef with appropriate arguments to process the file.

     Available options:
             Specify that a symbol is defined, and optionally specify what
             value to give it for the purpose of handling #if and #elif
     -Usym   Specify that a symbol is undefined.  If the same symbol appears
             in more than one argument, the last occurrence dominates.
     -c      If the -c flag is specified, then the operation of unifdef is
             complemented, i.e., the lines that would have been removed or
             blanked are retained and vice versa.
     -e      Because unifdef processes its input one line at a time, it cannot
             remove preprocessor directives that span more than one line.  The
             most common example of this is a directive with a multi-line
             comment hanging off its right hand end.  By default, if unifdef
             has to process such a directive, it will complain that the line
             is too obfuscated.  The -e option changes the behaviour so that,
             where possible, such lines are left unprocessed instead of
             reporting an error.
     -k      Process #if and #elif lines with constant expressions.  By
             default, sections controlled by such lines are passed through
             unchanged because they typically start "#if 0" and are used as a
             kind of comment to sketch out future or past development.  It
             would be rude to strip them out, just as it would be for normal
     -l      Replace removed lines with blank lines instead of deleting them.
     -o output
             The argument given is the name of an output file to be used
             instead of the standard output.  This file can be the same as the
             input file.
     -s      Instead of processing the input file as usual, this option causes
             unifdef to produce a list of symbols that appear in expressions
             that unifdef understands.  It is useful in conjunction with the
             -dM option of cpp(1) for creating unifdef command lines.
     -t      Disables parsing for C comments and line continuations, which is
             useful for plain text.
     -iUsym  Ignore #ifdefs.  If your C code uses #ifdefs to delimit non-C
             lines, such as comments or code which is under construction, then
             you must tell unifdef which symbols are used for that purpose so
             that it will not try to parse comments and line continuations
             inside those #ifdefs.  One specifies ignored symbols with
             -iDsym[=val] and -iUsym similar to -Dsym[=val] and -Usym above.
     -Ipath  Specifies to unifdefall an additional place to look for #include
             files.  This option is ignored by unifdef for compatibility with
             cpp(1) and to simplify the implementation of unifdefall.

     The unifdef utility copies its output to stdout and will take its input
     from stdin if no file argument is given.

     The unifdef utility works nicely with the -Dsym option of diff(1).

     Too many levels of nesting.

     Inappropriate #elif, #else or #endif.

     Obfuscated preprocessor control line.

     Premature EOF (with the line number of the most recent unterminated #if).

     EOF in comment.

     The unifdef utility exits 0 if the output is an exact copy of the input,
     1 if not, and 2 if in trouble.

     cpp(1), diff(1)

     The unifdef command appeared in 4.3BSD.  ANSI C support was added in
     FreeBSD 4.7.

     Expression evaluation is very limited.

     Preprocessor control lines split across more than one physical line
     (because of comments or backslash-newline) cannot be handled in every

     Trigraphs are not recognized.

     There is no support for symbols with different definitions at different
     points in the source file.

     The text-mode and ignore functionality does not correspond to modern
     cpp(1) behaviour.

BSD                              June 5, 2009                              BSD