Dear monks, this is very much a newbie question, but I rely on your kindness: I have a set of ligature instructions that I want to add to TeX property-list files. The general idea is simple: the original file reads 
(LABEL O 50)
   (KRN O 200 R -0.05)
...etc

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and this should become 
(LABEL O 50)
   (LIG O 50 O 2)
   (KRN O 200 R -0.05)
...etc

[download]
So I have this 
$_ =~ s/\(LABEL O 50\)/\(LABEL O 50\)\n   \(LIG O 50 O 200\)/;

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The problem is: not all the LABEL O XXX lines are already in the original file. Sometimes, I will have LIG instructions for a LABEL that does not exist yet. I know, e.g., that the instructions for the as yet nonexisting LABEL O 61 etc... must be placed between existing LABEL O 60 and LABEL O 62, but how can I instruct perl to include these instructions at the right address? Thanks so much for your help!!

In reply to adding lines at specific addresses by pindar

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