Well, here's a regex function that I made for that: 
  print is_quoted(q`I'm not quoted!`) . "\n" ;
  print is_quoted(q`"I'm \\"quoted!"`) . "\n" ;
  print is_quoted(q`"I'm not quoted!\"`) . "\n" ;
  print is_quoted(q`"I'm not \\\\"quoted!"`) . "\n" ;
  print is_quoted(q`""`) . "\n" ;
  print is_quoted(q`''`) . "\n" ;
  print is_quoted(q`"x"`) . "\n" ;
  print is_quoted(q`'x'`) . "\n" ;


#############
# IS_QUOTED #
#############

sub is_quoted {
  my $data = shift ;
  print "<<$data>>\n" ;
  
  $data =~ s/\\\\//gs ;   ## Ignore \\
  
  if (
  $data =~ /^             ## Begin
    \s*                   ## Ignore spaces in begin.
    (?:(?!\\).|)          ## Quote without \ before.
    (?:
      "[^"\\]?"                  ## Blank quoted or unique.
      |
      "(?:(?:\\")|[^"])+(?!\\)." ## quoted with values without " insid
+e, but accept \"
      |
      '[^'\\]?'                  ## Blank quoted or unique.
      |
      '(?:(?:\\')|[^'])+(?!\\).' ## quoted with values without ' insid
+e, but accept \'
    )
    \s*                   ## Ignore spaces in end.
  $/sx                    ## End. /x => extend space for the regex.
  ) { return( 1 ) ;} ## return true
  return 0 ;         ## return false

  ##better:
  # return undef ;
}

[download]
Note that I ignore spaces before and after the quoted values. If you don't want, just remove the \s* from the regex.

I have added the print() inside the function just to follow the tests. Here's the output: 

<<I'm not quoted!>>
0
<<"I'm \"quoted!">>
1
<<"I'm not quoted!\">>
0
<<"I'm not \\"quoted!">>
0
<<"">>
1
<<''>>
1
<<"x">>
1
<<'x'>>
1

[download]

Enjoy!

Graciliano M. P.
"The creativity is the expression of the liberty".

In reply to Re: Test if string is already quote()'d? (REGEX rox) by gmpassos
in thread Test if string is already quote()'d? by Seumas

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.