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cppawk(1) cppawk manual cppawk(1)
NAME
cppawk - wrapper for awk, with C preprocessing
SYNOPSIS
cppawk [cpp and awk options ]
cppawk --prepro-only [cpp and awk options]
DESCRIPTION
cppawk is a shell script which passes awk code through the standalone C preprocessor, and
then invokes awk on the preprocessed code. This allows Awk code to be written which uses C
preprocessor #define macros, #include C comments, trigraphs (though perish the thought)
and backslash continuation.
cppawk deliberately has an invocation syntax similar to Awk, and understands certain Awk
options such as -f and also understands cpp options, such as -Dfoo=bar for pre-defining a
macro.
Just like with awk, code is specified either directly as the first non-option argument, or
via the -f option which indicates a file. In either situation, cppawk preprocesses the
code and places the result in a temporary file which is then executed as awk code.
When cppawk installation is configured to use GNU Awk, which is the default, the pre-
processor symbol __gawk__ is predefined with a value of 1.
OPTIONS
Any option not described here is assumed to be an Awk option which takes no argument, and
is consequently passed through to the awk program.
-- End of options: any subsequent argument is the first non-option argument, even if
it looks like an option.
--prepro-only
Do not run the preprocessed Awk program; dump the preprocessed code to standard
output.
-f filename
Read the awk program from filename rather than processing awk code from the first
non-option command-line argument. The program is preprocessed to a temporary file,
and awk is then invoked on this file. The file is deleted when awk terminates.
-M, --bignum
These two equivalent GNU Awk options are passed through to awk, which will under-
stand them if it is GNU Awk. Using either of them causes the preprocessor symbol
__bignum__ to be defined with the value 1.
-P, --posix
These two equivalent GNU Awk options are passed through to awk, which will under-
stand them if it is GNU Awk. Using either of them causes the preprocessor symbol
__posix__ to be defined with the value 1.
-M... Any optional argument beginning with -M and followed by one or more characters re-
sults in a diagnostic message and failed termination. The intent is that the -M
family of options that are supported by GNU cpp are not supported by cppawk.
-F, -v, -E, -i, -l, -L
These standard and GNU Awk options are recognizes by cppawk as requiring an argu-
ment. They are validated for the presence of the required argument, and passed to
awk.
-U..., -D..., -I..., -iquote...
Options which match these patterns are passed to the cpp program instead of awk.
STANDARD HEADERS
cppawk points the preprocessor to look for #include <...> files in its own directory. The
<stdver.h> header defines a preprocessor symbol __cppawk_ver whose value is a decimal in-
teger the form YYYYMMDD, such as 20220318.
EXAMPLES
Print the larger of field 1 or 2:
cppawk '// C comment
#define max(a, b) ((a) > (b) ? (a) : (b))
{ print max($1, $2) /* C comment */ } #awk comment'
Implement awk-like processing loop within function, to process /proc/mounts:
#include "awkloop.h"
function main()
{
awkloop ("/proc/mounts") {
rule ($3 != "ext4") { nextrec }
rule ($2 == "/") { print $1 }
}
}
BEGIN {
main()
}
Where awkloop.h contains:
#define awkloop(file) for (; getline < file || (close(file) && 0); )
#define nextrec continue
#define rule(cond) if (cond)
SEE ALSO
awk(1), cpp(6)
BUGS
The -f option can be given only once, whereas awk accepts multiple -f options, and exe-
cutes each of the indicated files.
Awk error messages are reported against the preprocessed text.
Awk # comments cannot be used at the start of a line because # begins a preprocessing di-
rective. They also cannot be used inside a preprocessing directive, such as a macro defi-
nition, because # is an operator in the preprocessor language. It may be a good idea to
avoid # comments entirely in cppawk source, and use only C comments.
The cpp program tokenizes text using C preprocessor rules. Because Awk is "C-like", there
is a lot of compatibility between that and Awk syntax, which is why cppawk works at all;
however, there may be corner cases where some issue arises because of this.
The choices of gawk and cpp are fixed in the source code; users must edit cppawk to select
alternative implementations or locations of these tools.
The C preprocessor's #include "..." directive is expected to search in the same directory
as the file in which it is located, which is critically important feature. However, cppawk
feeds the Awk code to cpp via a pipe, even in the case when source is specified via the -f
option. The reason is that the Awk source is filtered to remove the #! ("hash bang")
line, which cpp doesn't like. To make sure #include works as expected, cppawk inserts a
preprocessor option to add the original directory into the include file search path: the
current working directory in the case of Awk code specified in the command line, or else
the directory of the file specified via the -f option. In the default configuration, which
assumes the GNU C Preprocessor, the -iquote option is used for this; but in a configura-
tion using some preprocessor which does not have that option, it may have to be done via
the more heavy-handed -I option. These options are inserted before any preprocessor op-
tions that come from the cppawk command line.
AUTHOR
Kaz Kylheku <kaz@kylheku.com>
COPYRIGHT
Copyright 2022, BSD2 License.
Beta Version 18 March 2022 cppawk(1)
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