"The parentheses are used for the repeat factor. All my research on the internet indicates a multi-character pattern that needs to be repeated multiple times should be enclosed in parentheses. Is this not correct?"

Here's a test showing clustering and capturing. Both match as expected. Capturing also sets $1. 

$ perl -Mstrict -Mwarnings -E '
    my $re1 = qr{PV1\|1\|O\|(?:[^|]*\|){3}\|};
    my $re2 = qr{PV1\|1\|O\|([^|]*\|){3}\|};
    my $x = q{PV1|1|O|F3|F4|F5|F6|F7};
    my $y = q{PV1|1|O|F3|F4|F5||F7};
    say "------- Clustering -------";
    say "Match in \$x" if $x =~ /$re1/;
    say $1 if $1;
    say "Match in \$y" if $y =~ /$re1/;
    say $1 if $1;
    say "------- Capturing -------";
    say "Match in \$x" if $x =~ /$re2/;
    say $1 if $1;
    say "Match in \$y" if $y =~ /$re2/;
    say $1 if $1;
'
------- Clustering -------
Match in $y
------- Capturing -------
Match in $y
F5|

[download]

-- Ken

In reply to Re^3: Selecting HL7 Transactions by kcott
in thread Selecting HL7 Transactions by BillDowns

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