Ubuntu Manpage: unifdef, unifdefall — remove preprocessor conditionals from code

NAME

     unifdef, unifdefall — remove preprocessor conditionals from code

SYNOPSIS

     unifdef [-bBcdehKkmnsStV] [-Ipath] [-[i]Dsym[=val]] [-[i]Usym] ... [-f defile] [-x {012}]
             [-M backext] [-o outfile] [infile ...]
     unifdefall [-Ipath] ... file

DESCRIPTION

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, using
macros specified in -D and -U command line options or in -f definitions files. A directive
is processed if the macro specifications are sufficient to provide 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 macro is not specified.
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 macros 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.

When evaluating an expression, unifdef does not expand macros first. The value of a macro
must be a simple number, not an expression. A limited form of indirection is allowed, where
one macro's value is the name of another.

In most cases, unifdef does not distinguish between object-like macros (without arguments)
and function-like macros (with arguments). A function-like macro invocation can appear in
#if and #elif control expressions. If the macro is not explicitly defined, or is defined
with the -D flag on the command-line, or with #define in a -f definitions file, its
arguments are ignored. If a macro is explicitly undefined on the command line with the -U
flag, or with #undef in a -f definitions file, 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 macros and their
definitions (or lack thereof), then invokes unifdef with appropriate arguments to process
the file.

OPTIONS

-Dsym=val
Specify that a macro is defined to a given value.

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

-Usym Specify that a macro is undefined.

If the same macro appears in more than one argument, the last occurrence dominates.

-iDsym[=val]
-iUsym C strings, comments, and line continuations are ignored within #ifdef and #ifndef
blocks controlled by macros specified with these options.

-f defile
The file defile contains #define and #undef preprocessor directives, which have the
same effect as the corresponding -D and -U command-line arguments. You can have
multiple -f arguments and mix them with -D and -U arguments; later options override
earlier ones.

Each directive must be on a single line. Object-like macro definitions (without
arguments) are set to the given value. Function-like macro definitions (with
arguments) are treated as if they are set to 1.

-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 Complement, i.e., lines that would have been removed or blanked are retained and
vice versa.

-d Turn on printing of debugging messages.

-e By default, unifdef will report an error if it needs to remove a preprocessor
directive that spans more than one line, for example, if it has a multi-line comment
hanging off its right hand end. The -e flag makes it ignore the line instead.

-h Print help.

-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.

-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 comments.

-m Modify one or more input files in place.

-M backext
Modify input files in place, and keep backups of the original files by appending the
backext to the input filenames.

-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 when processing a
single file.

-s Instead of processing an input file as usual, this option causes unifdef to produce
a list of macros that are used in preprocessor directive controlling expressions.

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

-t Disables parsing for C strings, comments, and line continuations, which is useful
for plain text. This is a blanket version of the -iD and -iU flags.

-V Print version details.

-x {012}
Set exit status mode to zero, one, or two. See the EXIT STATUS section below for
details.

The unifdef utility takes its input from stdin if there are no file arguments. You must use
the -m or -M options if there are multiple input files. You can specify inut from stdin or
output to stdout with ‘-’.

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

EXIT STATUS

     In normal usage the unifdef utility's exit status depends on the mode set using the -x
     option.

     If the exit mode is zero (the default) then unifdef exits with status 0 if the output is an
     exact copy of the input, or with status 1 if the output differs.

     If the exit mode is one, unifdef exits with status 1 if the output is unmodified or 0 if it
     differs.

     If the exit mode is two, unifdef exits with status zero in both cases.

     In all exit modes, unifdef exits with status 2 if there is an error.

     The exit status is 0 if the -h or -V command line options are given.

DIAGNOSTICS

     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.

HISTORY

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

AUTHORS

     The original implementation was written by Dave Yost <Dave@Yost.com>.
     Tony Finch <dot@dotat.at> rewrote it to support ANSI C.

BUGS

     Expression evaluation is very limited.

     Handling one line at a time means preprocessor directives split across more than one
     physical line (because of comments or backslash-newline) cannot be handled in every
     situation.

     Trigraphs are not recognized.

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

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

                                         January 7, 2014