If the data has already been read into the variable $data as a single string, then just replace the line:

if (my ($field) = grep { /^!!./ } split /\|/, do { local $/; <DATA> })
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with:

if (my ($field) = grep { /^!!./ } split /\|/, $data)
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(The expression do { local $/; <DATA> } slurps the whole of the data in from the __DATA__ block at the foot of the script.)

Hope that helps,