When I first read the OP, the phrase "matched pattern" triggered an "I know, I'll use a regex..." knee-jerk response, and I formulated the problem statement "keep the first n occurrences of a pattern in a string along with any intervening matter and delete all occurrences thereafter".

It turns out that a regex-based approach is not appropriate for the OPed problem unless it be a "keep all lines that match a given regex" strategy, which would, IMHO, be quite good because it combines a possibly quite large element of validation with data extraction and is also completely scaleable.

In any event, proceeding along the lines of my first-but-not-necessarily-best thought, I came up with this, which may be of interest: 

>perl -wMstrict -le
"my $s = 'x foo1 foo2 x foo3 x yfoo9 foo4 foo5 foo9y x foo6 foo7 x';
 print qq{'$s' \n};
 ;;
 my $pat = qr{ \b foo \d \b }xms;
 ;;
 for my $n (0 .. 4) {
   (my $t = $s) =~ s{ \A (?: .*? $pat){$n} \K | $pat }''xmsg;
   print qq{'$t'};
   }
"
'x foo1 foo2 x foo3 x yfoo9 foo4 foo5 foo9y x foo6 foo7 x'

'x   x  x yfoo9   foo9y x   x'
'x foo1  x  x yfoo9   foo9y x   x'
'x foo1 foo2 x  x yfoo9   foo9y x   x'
'x foo1 foo2 x foo3 x yfoo9   foo9y x   x'
'x foo1 foo2 x foo3 x yfoo9 foo4  foo9y x   x'

[download]

Update: I should add that the  \K regex operator used above is available with Perl versions 5.10+.

In reply to Re: Removing matched pattern except the first pattern by AnomalousMonk
in thread Removing matched pattern except the first pattern by rahulruns

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