I'm not sure what you want. If shenme's reply doesn't help, this might:

while (<DATA>) {
  print if (/string1/../string2/) && /string3/;
  # Only prints "string3 2"
}

__DATA__
bla
bla
string3 1
foo
foo
string1
bar
bar
string3 2
bah
bah
string2
feh
feh
string3 3
moo
moo
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