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Match Delimited Text

Remove C comments....
|> The input file has a declaration something like the following with
|> several comments in a single line:
|>
|>    input a, b, /* comment  */ c, /* comment ******************* */ d;
|>
|> I need to delete the comments in between and write the declaration as
|>
|>    input a, b, c, d;
|>
|> NOTE: the c, must not be deleted.

It's a standard match-delimited-text problem, and the general solution is:

  1: match the opening delimiter
  2: match stuff that's not the closing delimiter
  3: match the closing delimiter

In this case, the opening delimiter is "/*" so the regex is "/\*".
The closing delimiter is "*/", so that regex is "\*/".

Stuff that's not the closing delimiter would be
        A) anything that's not /                  (regex "[^/]" )
   and  B) any / so long as it has no * before it (regex "[^*]/")

Combining them with an indication to say "as much as is there", we get:

        ([^/]|[^*]/)*

So the whole regex, wrapped in some perl, would be:

                               s#/\*([^/]|[^*]/)*\*/##g;
Parts number from above:         1112222222222222333
                                     AAAA BBBB

Note that there's another way to conceptually look at the "stuff not the
closing delimiter". That'd be:
        A) anything not a *   (regex "[^*]")
   and  B) any * so long as it's not followed by a / (regex "\*[^/]")

That would lead to
        s#/\*([^*]|\*[^/])*\*/##g;

However, since the "\*[^/]" eats a character, it could eat the third * in
the string "/* commet **/" and we'd wedgie the regex and it wouldn't match.

The first way described above only eats characters we've already had a
chance to check aren't the ending, so it won't wedgie.
                               Jeffrey Friedl  <jfriedl@nff.ncl.omron.co.jp>

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Spliting Quote Delimited Fields (CSV)

EG: spliting CVS data (a comma delimited file with quoted fields)
Example:
   SAR001,"","Cimetrix, Inc","Bob Smith","CAM","\"",N,8,,"Error, Core Dumped"

undef @fields;
push( @fields, defined($1) ? $1 : $3)
   while  m/"([^"\\]*(\\.[^"\\]*)*)"|([^,]+)/g;

WARNING the above does not seem to work under perl 5 -- Anthony


Jeffrey Friedl, author of Mastering Regular Expressions gives...

  @new = ();
  push(@new, $+) while $text =~ m{
          "([^\"\\]*(?:\\.[^\"\\]*)*)",?  # groups the phrase inside the quotes
          | ([^,]+),?
          | ,
          }gx;
  push(@new, undef) if substr($text,-1,1) eq ',';

However quotes within a quoted field needs to be backslashed using \"

Alternatively, use Text::ParseWords

  use Text::ParseWords;
  @new = quotewords(",", 0, $text);


For space separated words such as for a shell command
EG:     cp -p "my file" "yourfile"
you can look at...
  perl4:  shellwords.pl library,
  perl5:  Text::ParseWords module

    perl -de 1
        use Text::ParseWords
        $line = 'cp -p "my file" "your file"'
        @words = shellwords $line
        X words
        @words = (
          0  'cp'
          1  '-p'
          2  'my file'
          3  'your file'
        )

Perl 4 Alturnatives...

Method 1:
    # delimit ','  with quoted strings and variable allowed
    $_ = 'f1,f 2,"f3","f,4",5,$time,f7';
    while (/,|"|$/go) {
      ($within = ($within ? 0 : 1), next) if '"' eq $&;
      next if $within;
      substr($_, 0, length($`)+1) = "";
      push(@fields, $`);
    }
    print join("    ", @fields),"\n";

  output
  f1    f 2    "f3"    "f,4"    5    $time    f7

Method 2:
  Just remove the delimiter ',' from within quotes
    s/("[^"]*")/do{$a = $1; $a =~ tr#,#c#; $a;}/ge;
  now you can split the line as you would normally
  If you substitute the ',' with a unused char you can restore it later!

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