On 3/9/07, John W. Krahn <[EMAIL PROTECTED]> wrote:
Chas Owens wrote:
> On 3/8/07, Dharshana Eswaran <[EMAIL PROTECTED]> wrote:
>>
>> I need to extract few strings from one file and paste it to another
file.
> snip
>
> This doesn't seem like a good job for split. The split function is
> good for parsing X separated records where X is either constant or
> simple. What you have there a grammar. Specifically a subset of the
> C grammar for #define. With grammars you want to use either a regex
> or Parse::RecDescent depending on the complexity of the grammar. In
> this case the grammar is simple enough that a regex does fine. I have
> created a regex that parses your record into a name, base number,
> operator, and modifying number. The last two values are optional. I
> have used the x option on the regex to make it readable since it is so
> large (anything bigger than 80 characters should probably use the x
> option). You can learn more about regexes in perldoc perlre and
> perldoc perlretut.
>
> #!/usr/bin/perl
>
> use strict;
> use warnings;
>
> while (<DATA>) {
> my ($name, $base, $op, $mod) = m{
> ^ # start of string
> \s* # optional spaces
> \#define # the start of the macro
The C preprocessor allows whitespace between '#' and 'define'.
\# \s* define # the start of the macro
> \s+ # mandatory spaces
> (\w+) # capture the name of the macro
> \s* # optional spaces
If the next token is a left parenthesis then the whitespace is not
optional
otherwise it would be a macro definition. Also, if the next token is a
word
character then the whitespace is not optional.
> \( # the open paren
> \s* # optional spaces
> (
> \w+ |
> \d+ |
> 0x[a-fA-F0-9]
That only matches a single hexadecimal digit, you probably want
0x[a-fA-F0-9]+
instead.
> ) # capture a word, int, or hex
> \s* # optional spaces
> (?:
> ( # capture the various int operators
> [+-|^*/%] |
[+-|^&*/%] |
> << |
> >>
> )
What about:
TOKEN & ~TOKEN
Or:
TOKEN * -TOKEN
:-)
> \s* # optional spaces
> ( # capture a word, int, or hex
> \w+ |
> \d+ |
> 0x[a-fA-F0-9])
0x[a-fA-F0-9]+)
> )? # but make the last two captures
> optional
> \) # the close paren
> }x;
> $op = $mod = '' unless defined $op;
> print;
> print "\tname is $name, base is $base, modified by $mod using
$op\n"
> if $name;
> }
John
--
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certain sorts of tools at low cost and in short order. -- Larry Wall
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Thank you for the suggestions. I tried both ways.
0x[a-fA-F0-9]
That only matches a single hexadecimal digit, you probably want
0x[a-fA-F0-9]+
instead.
When i tried Chas's idea, without this correction itself i could get the hex
values more than a digit.
But i did not understand the below lines mentioned by John.
What about:
TOKEN & ~TOKEN
Or:
TOKEN * -TOKEN
:-)
Can you please explain it?
Thanks once again for the immediate response.
Thanks and Regards,
Dharshana
