Shell Programming and Scripting

They are "B*", your one column file is represented by "file"

Also the first column should have only A17_1T

Code:

FNR==NR {
  f2[FNR]=$0
  next
}
FNR==1 {n=split(FILENAME,t,"[_.]");f=t[n-2] "_" t[n-1];next}
# or
# FNR==1 {match(FILENAME,"_[^_][^_]*_[^_][^_]*[.]"); f=substr(FILENAME,RSTART+1,RLENGTH-2);next}
{ print f, f2[FNR-1], $3}

Yes, you are correct the substr statement you quoted takes 3 characters starting at position 3 of the filename and substr(FILENAME,10,3 takes 3 characters starting from position 10. As the two substr are next to each other they are joined together.

I'm not sure this approach is going to work out for you, the approach taken by the other solutions posted here involves matching on the Underscore(_) character and might be more flexable depending on your actual filenames.