Multi-line efetch digging
Not exactly what you were looking for but may be you can use something like this?
ncbi2=NC_002021
efetch -db protein -format gpc -id &quot;$ncbi2&quot; \
    | xtract -pattern INSDSeq_feature-table \
        -group INSDFeature \
        -if INSDFeature_key -equals 'mat_peptide' \
        -tab '\n' \
        -element INSDFeature_location,INSDQualifier_value \
    | grep 'Segment 2'

For explorations of the INSDSet XMLs, xtract has -insd option that you can use. In this particular case, you can do something like this:
efetch -db nuccore -id &quot;$ncbi2&quot; -format gpc \
    | xtract -insd mat_peptide product peptide

For more information, checkout EDirect documentation and some  example queries