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unifdef appeared in 4.1c before 2.9
dates checked in CSRG archives and already changed upstream in unifdef3

.\"	$OpenBSD: unifdef.1,v 1.31 2023/08/13 02:20:23 jsg Exp $
.\" Copyright (c) 1985, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\" Copyright (c) 2002 - 2013 Tony Finch <dot@dotat.at>.  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" Dave Yost. It was rewritten to support ANSI C by Tony Finch.
.\"
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.\" modification, are permitted provided that the following conditions
.\" are met:
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.\"    notice, this list of conditions and the following disclaimer.
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.\"    may be used to endorse or promote products derived from this software
.\"    without specific prior written permission.
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.Dd $Mdocdate: August 13 2023 $
.Dt UNIFDEF 1
.Os
.Sh NAME
.Nm unifdef
.Nd remove preprocessor conditionals from code
.Sh SYNOPSIS
.Nm
.Op Fl BbcdehKkmnSstV
.Op Fl Oo Cm i Oc Ns Cm D Ns Ar sym Ns Op = Ns Ar val
.Op Fl Oo Cm i Oc Ns Cm U Ns Ar sym
.Op Fl f Ar defile
.Op Fl M Ar backext
.Op Fl o Ar outfile
.Op Fl x Cm 0 | 1 | 2
.Ar
.Sh DESCRIPTION
The
.Nm
utility selectively processes conditional
.Xr 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.
.Pp
The
.Nm
utility acts on
.Ic #if , #ifdef , #ifndef ,
.Ic #elif , #else ,
and
.Ic #endif
lines,
using macros specified in
.Fl D
and
.Fl U
command line options or in
.Fl f
definition 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
.Ic #ifdef
or
.Ic #ifndef
directive is passed through unchanged
if its controlling macro is not specified.
Any
.Ic #if
or
.Ic #elif
control expression that has an unknown value or that
.Nm
cannot parse is passed through unchanged.
By default,
.Nm
ignores
.Ic #if
and
.Ic #elif
lines with constant expressions;
it can be told to process them by specifying the
.Fl k
flag on the command line.
.Pp
It understands a commonly-used subset
of the expression syntax for
.Ic #if
and
.Ic #elif
lines:
integer constants,
integer values of macros defined on the command line,
the
.Fn defined
operator,
the operators
.Ic \&! , < , > ,
.Ic <= , >= , == , != ,
.Ic && , || ,
and parenthesized expressions.
A kind of
.Dq "short circuit"
evaluation is used for the
.Ic &&
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
.Ic ||
is definitely true then the result is true.
.Pp
When evaluating an expression,
.Nm
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.
.Pp
In most cases,
.Nm
does not distinguish between object-like macros
(without arguments) and function-like macros (with arguments).
A function-like macro invocation can appear in
.Ic #if
and
.Ic #elif
control expressions.
If the macro is not explicitly defined,
or is defined with the
.Fl D
flag on the command-line,
or with
.Ic #define
in a
.Fl f
definition file,
its arguments are ignored.
If a macro is explicitly undefined on the command line with the
.Fl U
flag,
or with
.Ic #undef
in a
.Fl f
definition file,
it may not have any arguments since this leads to a syntax error.
.Pp
The
.Nm
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.
.Pp
The options are as follows:
.Pp
.Bl -tag -width indent -compact
.It Fl B
Compress blank lines around a deleted section.
Mutually exclusive with the
.Fl b
option.
.Pp
.It Fl b
Replace removed lines with blank lines
instead of deleting them.
Mutually exclusive with the
.Fl B
option.
.Pp
.It Fl c
Complement.
That is, lines that would have been removed or blanked
are retained and vice versa.
.Pp
.Sm off
.It Xo
.Fl D Ar sym
.Op = Ar val
.Xc
.Sm on
.It Fl U Ns Ar sym
Specify that a macro is defined
.Pq Fl D
to a given value,
to 1 if no value is given,
or undefined
.Pq Fl U .
.Pp
If the same macro appears in more than one argument,
the last occurrence dominates.
.Pp
.It Fl d
Turn on printing of debugging messages.
.Pp
.It Fl e
By default,
.Nm
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
.Fl e
flag makes it ignore the line instead.
.Pp
.It Fl f Ar defile
The file
.Ar defile
contains
.Ic #define
and
.Ic #undef
preprocessor directives,
which have the same effect as the corresponding
.Fl D
and
.Fl U
command line arguments.
Multiple
.Fl f
arguments can be given and mixed with
.Fl D
and
.Fl U
arguments;
later options override earlier ones.
.Pp
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.
.Pp
.Sm off
.It Xo
.Fl iD Ar sym
.Op = Ar val
.Xc
.Sm on
.It Fl iU Ns Ar sym
Ignore
.Ic #ifdef Ns s .
If C code uses
.Ic #ifdef Ns s
to delimit non-C lines,
such as comments
or code which is under construction,
this tells
.Nm
which symbols are used for that purpose so that it will not try to parse
comments and line continuations
inside those
.Ic #ifdef Ns s .
.Pp
If the same macro appears in more than one argument,
the last occurrence dominates.
.Pp
.It Fl h
Print help.
.Pp
.It Fl K
Always treat the result of
.Ic &&
and
.Ic ||
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
.Nm .
.Pp
.It Fl k
Process
.Ic #if
and
.Ic #elif
lines with constant expressions.
By default, sections controlled by such lines are passed through unchanged
because they typically start
.Dq Li "#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.
.Pp
.It Fl M Ar backext
Modify input files in place, and keep backups of the original files by
appending the
.Ar backext
to the input filenames.
If a zero length
.Ar backext
is given, no backup will be saved.
.Pp
.It Fl m
Modify one or more input files in place.
.Pp
.It Fl n
Add
.Li #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.
.Pp
.It Fl o Ar outfile
Write output to the file
.Ar outfile
instead of the standard output when processing a single file.
.Pp
.It Fl S
Like the
.Fl 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.
.Pp
.It Fl s
Instead of processing an input file as usual,
this option causes
.Nm
to produce a list of macros that are used in
preprocessor directive controlling expressions.
.Pp
.It Fl t
Disables parsing for C strings, comments,
and line continuations,
which is useful
for plain text.
This is a blanket version of the
.Fl iD
and
.Fl iU
flags.
.Pp
.It Fl V
Print version details.
.Pp
.It Fl x Cm 0 | 1 | 2
Set exit status mode to zero, one, or two.
See the
.Sx EXIT STATUS
section below for details.
.El
.Pp
The
.Nm
utility takes its input from
.Em stdin
if there are no
.Ar file
arguments.
The
.Fl m
or
.Fl M
options must be used if there are multiple input files.
A dash
.Pq -
specifies input from stdin or output to stdout.
.Pp
The
.Nm
utility works nicely with the
.Fl D
option of
.Xr diff 1 .
.Sh EXIT STATUS
In normal usage the
.Nm
utility's exit status depends on the mode set using the
.Fl x
option.
.Pp
If the exit mode is zero (the default) then
.Nm
exits with status 0 if the output is an exact copy of the input,
or with status 1 if the output differs.
.Pp
If the exit mode is one,
.Nm
exits with status 1 if the output is unmodified
or 0 if it differs.
.Pp
If the exit mode is two,
.Nm
exits with status zero in both cases.
.Pp
In all exit modes,
.Nm
exits with status 2 if there is an error.
.Pp
The exit status is 0 if the
.Fl h
or
.Fl V
command line options are given.
.Sh DIAGNOSTICS
.Bl -item
.It
.Tn EOF
in comment
.It
Inappropriate
.Ic #elif ,
.Ic #else
or
.Ic #endif
.It
Obfuscated preprocessor control line
.It
Premature
.Tn EOF
(with the line number of the most recent unterminated
.Ic #if )
.It
Too many levels of nesting
.El
.Sh SEE ALSO
.Xr cpp 1 ,
.Xr diff 1
.Pp
The unifdef home page is
.Lk https://dotat.at/prog/unifdef .
.Sh HISTORY
The
.Nm
command appeared in
.Bx 4.1c .
.Tn ANSI\~C
support was added in
.Fx 4.7 .
.Sh AUTHORS
The original implementation was written by
.An Dave Yost Aq Mt Dave@Yost.com .
.An Tony Finch Aq Mt dot@dotat.at
rewrote it to support
.Tn ANSI\~C .
.Sh BUGS
Expression evaluation is very limited.
.Pp
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.
.Pp
Trigraphs are not recognized.
.Pp
There is no support for macros with different definitions at
different points in the source file.
.Pp
The text-mode and ignore functionality does not correspond to modern
.Xr cpp 1
behaviour.