>perl -ane "next unless $F[0]=~/^ZJ/;$count++;$val+=$F[8]}{printf qq|%
+d values; mean=%.4f\n|,$count,$val/$count" source.file.name.txt
#OUTPUT:
6 values; mean=-1.1958
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Use single-quotes for Linux. Format, and redirect output as desired.
see "perl --help" for the meanings of -a, -n, -e, and @F
"}{" is the perl eskimo greeting.