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261 lines
7.0 KiB
Plaintext
261 lines
7.0 KiB
Plaintext
Preprocessor
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============
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This is a very primitive line based preprocessor, for times when using
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a C preprocessor isn't an option.
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Instructions
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------------
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Any line starting with a hash # and a letter is considered to be a
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preprocessor instruction. Other lines starting with a hash are ignored
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as comments.
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The following preprocessor instructions are recognised.
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#define VARIABLE
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#define VARIABLE STRING
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#undef VARIABLE
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#ifdef VARIABLE
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#ifndef VARIABLE
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#if VARIABLE
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#if !VARIABLE
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#if VARIABLE==STRING
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#if VARIABLE!=STRING
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#else
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#elifdef VARIABLE
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#elifndef VARIABLE
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#elif VARIABLE
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#elif !VARIABLE
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#elif VARIABLE==STRING
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#elif VARIABLE!=STRING
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#endif
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#error STRING
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#include FILENAME
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#includesubst @VAR@FILENAME
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#expand STRING
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#literal STRING
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#filter FILTER1 FILTER2 ... FILTERn
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#unfilter FILTER1 FILTER2 ... FILTERn
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Whitespace is significant -- for instance, '#define TEST foo' is not
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the same as '#define TEST foo '. The first defines TEST to be a three
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character string, the second defines it to be four characters long.
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The conditionals (#ifdef, #ifndef, #if, #else, #elifdef, #elifndef,
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#elif, #endif) can be nested to arbitrary depth.
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An #else section can be followed by an #else section, as in:
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#if 1
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used
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#else
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not used
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#else
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used again
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#endif
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Whether this is wise or not is left up to the reader to decide.
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The #elifdef, #elifndef, and #elif instructions are equivalent to
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#else instructions combined with the relevant conditional. For
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example,
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#ifdef foo
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block 1
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#elifdef bar
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block 2
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#endif
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...could be written as:
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#ifdef foo
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block 1
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#else
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#ifdef bar
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block 2
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#endif
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#endif
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#else blocks need not come last, which can lead to some odd
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constructs.
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#ifdef foo
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included if foo is defined
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#else
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included if foo is not defined
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#elifdef bar
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included if foo is defined and bar is defined
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#else
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included if either foo or bar are not defined
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#endif
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Note in particular the following holds:
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#if 1
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always included
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#elif 1
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never included
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#else
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always included
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#endif
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That is to say, #else is relative to whether the previous conditional
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was included _only_. It isn't an "and" relationship with previous
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conditionals. This is arguably a bug.
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The #error instruction stops execution at this point with a fatal
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error. The error message will include the given STRING.
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The #include instruction causes the specified file FILENAME to be
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recursively processed, as if it was inserted at the current position
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in the file. This means conditionals can be started in one file and
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ended in another, although this practice is strongly discouraged.
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There is no predefined limit to the depth of #includes, and there is
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no restriction on self-inclusion, so care should be taken to avoid
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infinite loops.
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The #includesubst instruction behaves like #include, except that any
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variables in @ATSIGNS@ are expanded, like the substitution filter.
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The #expand instruction will print the given STRING with variable
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substitutions. See the substitution section below.
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The #literal instruction will print the given STRING with a newline,
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with absolutely no other fixups, guaranteed. This can be used to
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output lines starting with a #, which would otherwise be stripped out
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as comments.
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The #filter instruction enables the specified filters. You can turn
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off filters using #unfilter. See the Filters section below.
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Variables
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---------
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Variables consist of any alphanumeric string. They are defined using
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the -D command line argument and the #define instruction.
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To define all environment variables, so that you can use __HOME__,
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etc, with #expand, use the -E argument. Note that arguments that use
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non-word characters (like "!") are not included. (In particular,
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cygwin is known to include all kinds of weird characters in its
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environment variables.)
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Two special variables are predefined, FILE and LINE. They can be
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passed to #define and #undef, but FILE is automatically redefined at
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the top of each file, and LINE is increased by one at the start of
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each line.
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The variable '1' is predefined with value 1. The variable '0' is not
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defined. This allows constructs such as
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#if 0
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...
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#endif
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...to be used to quickly comment out large sections. Note, however,
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that these are simply variables, and can be redefined. This is
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strongly discouraged.
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Substitution
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------------
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In any line starting with the instruction #expand, variable names
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contained between double underscores, like __THIS__, are expanded to
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their string values, or the empty string if they are not defined.
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For example to print the current filename:
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#expand <!-- This file is automatically generated from __FILE__ -->
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Normal lines are not affected.
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See also the substitution filter below.
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Filters
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-------
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The following filters are supported:
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emptyLines
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Strips blank lines from the output.
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slashslash
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Strips everything from the first two consecutive slash (/)
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characters until the end of the line.
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spaces
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Collapses sequences of spaces into a single space.
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substitution
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Replaces occurrences of "@foo@" by the value of the variable
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"foo". If @foo@ is not defined, the preprocessor will terminate
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with a fatal error.
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attemptSubstitution
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Replaces occurrences of "@foo@" by the value of the variable
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"foo". If @foo@ is not defined, the empty string is used instead.
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Filters are run in alphabetical order, on a per-line basis.
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Command Line Arguments
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----------------------
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Syntax:
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preprocessor.pl [-Dvariable[=value]] [-E] [-Ffilter]
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[-Ifilename] [-d] [--marker=<c>] [--] filenames...
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-Dvariable
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Set variable to 1 before processing the files.
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-Dvariable=value
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Set variable to value before processing the files.
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-E
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Define all environment variables.
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-Ffilter
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Enables the specified filter.
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-Ifilename
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Include filename before any other files.
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-d
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Run through the files on the command line, listing the files they
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depend on given the specified environment variables and filters.
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Doesn't recurse into those files. The output is given as one
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dependency per line, and filenames are given relative to the
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current directory.
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--line-endings=type
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Set the type of line endings to use. "type" can be either "cr",
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"lf", or "crlf". The default is whatever your platform uses for
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perl's "\n" character.
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--marker=<c>
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Use the character <c> instead of '#' as the marker for preprocessor
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instructions.
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--
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Indicates the end of non-filename arguments.
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-
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Indicates that input should come from standard input.
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If no filenames are provided, standard input is used instead. If many
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files are provided, they are processed sequentially, as if they were
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one big file. -I files are handled before the other files, in the
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order specified, but after handling any -D, -E, -F, and -d arguments.
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Contact Details
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---------------
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Feel free to e-mail me if you have any questions:
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Ian Hickson <preprocessor@software.hixie.ch>
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