Hi ikegami,

Thanks for your example. I'm still trying to figure it all out. I'm running it as below, and it doesn't seem to quite do what I want. I only want the escape character to be treated specially if it's in !+; - i.e. a!!b should be a!!b, whereas a!!!;b should be a!;b.

Also, I seem to be getting an empty field at the end. One or more semicolons at the end seem to be parsed properly, though.

One test string returns a blank result. ?

sub dequote {
    my $x = $_[0];
    $x =~ s/!(.)/$1/sg;
    return $x;
}

while(<>) {
    chomp;
    my @fields = map dequote($_), /\G((?:[^!;]+|!.)*)(?:;|\z)/sg;
    print "$_ => " . join( '|', @fields ) . "\n";
#     print "$_ => @fields\n";
}
[download]

Sample results:

aval!!!!;bval => aval!!|bval|
aval!!!!!;bval => aval!!;bval|
a!!val!!!!!;bval! =>
!a!!!val!!!!!;bval!! => a!val!!;bval!|
a!val!;bva!l; => aval;bval|
a!!val!!;;bv!!al;; => a!val!||bv!al||
[download]

I only want the escape character to be treated specially if it's in !+;

Yuck! I hope you're being forced to deal with this format.

It's not only tricker for a human to understand, it's tricker to code. In particular, the definition of a field varies based on whether it's the last field or not, and the function of the "!" varies based on its position in the field.

sub unescape {
    my $x = $_[0];
    my ($base, $end) = $x =~ /^(.*)(!+)\z/s;
    return $base . ('!' x (length($end)/2));
}

my $last_field = qr/
   [^;]*
/x;

my $other_field = qr/
   (?: [^!]+
   |   (?: ![^!] )+
   )*
   (?:!!)*
/x;

# Validation
my $record = qr/^ (?: $other_field ; )* $last_field \z/x;

# Extraction
my @fields = map unescape($_), /
   \G
   ( $other_field (?= ; )
   | $last_field  (?= \z )
   )
   (?:;|\z)
/xg;
[download]

You are free to skip the validation.