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UNIFDEF(1)              FreeBSD General Commands Manual             UNIFDEF(1)

     unifdef, unifdefall - remove preprocessor conditionals from code

     unifdef [-bBcdeKknsStV] [-Ipath] [-Dsym[=val]] [-Usym] [-iDsym[=val]]
             [-iUsym] ... [-o outfile] [infile]
     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.  A directive is only processed if the symbols specified on
     the command line are sufficient to allow unifdef to get a definite value
     for its control expression.  If the result is false, the directive and
     the following lines under its control are removed.  If the result is
     true, only the directive is removed.  An #ifdef or #ifndef directive is
     passed through unchanged if its controlling symbol is not specified on
     the command line.  Any #if or #elif control expression that has an
     unknown value or that unifdef cannot parse is passed through unchanged.
     By default, unifdef ignores #if and #elif lines with constant
     expressions; it can be told to process them by specifying the -k flag on
     the command line.

     It understands a commonly-used subset of the expression syntax for #if
     and #elif lines: integer constants, integer values of symbols defined on
     the command line, the defined() operator, the operators !, <, >, <=, >=,
     ==, !=, &&, ||, and parenthesized expressions.  A kind of ``short
     circuit'' evaluation is used for the && operator: if either operand is
     definitely false then the result is false, even if the value of the other
     operand is unknown.  Similarly, if either operand of || is definitely
     true then the result is true.

     In most cases, the unifdef utility does not distinguish between object-
     like macros (without arguments) and function-like arguments (with
     arguments).  If a macro is not explicitly defined, or is defined with the
     -D flag on the command-line, its arguments are ignored.  If a macro is
     explicitly undefined on the command line with the -U flag, it may not
     have any arguments since this leads to a syntax error.

     The unifdef utility 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 for it 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.

             Specify that a symbol is defined to a given value which is used
             when evaluating #if and #elif control expressions.

     -Dsym   Specify that a symbol is defined to the value 1.

     -Usym   Specify that a symbol is undefined.  If the same symbol appears
             in more than one argument, the last occurrence dominates.

     -b      Replace removed lines with blank lines instead of deleting them.
             Mutually exclusive with the -B option.

     -B      Compress blank lines around a deleted section.  Mutually
             exclusive with the -b option.

     -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.

     -d      Turn on printing of debugging messages.

     -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      Always treat the result of && and || operators as unknown if
             either operand is unknown, instead of short-circuiting when
             unknown operands can't affect the result.  This option is for
             compatibility with older versions of unifdef.

     -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

     -n      Add #line directives to the output following any deleted lines,
             so that errors produced when compiling the output file correspond
             to line numbers in the input file.

     -o outfile
             Write output to the file outfile instead of the standard output.
             If outfile is the same as the input file, the output is written
             to a temporary file which is renamed into place when unifdef
             completes successfully.

     -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.

     -S      Like the -s option, but the nesting depth of each symbol is also
             printed.  This is useful for working out the number of possible
             combinations of interdependent defined/undefined symbols.

     -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.  You can specify 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.

     -V      Print version details.

     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).

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

     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.

     cpp(1), diff(1)

     The unifdef command appeared in 2.9BSD.  ANSI C support was added in
     FreeBSD 4.7.

     The original implementation was written by Dave Yost <>.
     Tony Finch <> rewrote it to support ANSI C.

     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.

FreeBSD 11.0-PRERELEASE         March 11, 2010         FreeBSD 11.0-PRERELEASE


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