Regexp to extract value of src attribute; handles single-quoted values, double-quoted values, and values without quotes (they must not contain any whitespace or quotes).

my $reSqString = qr{
  \'
  [^\']*
  \'
}x;

my $reDqString = qr{
  \"
  [^\"]*
  \"
}x;

my $reAttrValue = qr{
  (?: $reSqString | $reDqString | [^\'\"\s]+ )
}x;

my $reImgSrc =
    qr{
      <[iI][mM][gG]
        \s+
      (?: \w+ \s*=\s* $reAttrValue \s+ )*
      [sS][rR][cC] \s*=\s*
      (?: (?:\'([^\']+)\') | (?:\"([^\"]+)\") | ([^\'\"\s]+) )
      (?: \s+ \w+ \s*=\s* $reAttrValue )*
      \s*/?>
    }x;

• testhtmlregexp: Script to test a regexp for extracting an attribute value from an HTML tag