Answer by cuonglm for Grep for a line containing only 5 or 6 numbers

Another perl:

$ perl -MList::Util=first -Tnle '
  s/^\s+|\s+$//g;
  @e = split /\s+/;
  print if @e == 5 || @e == 6 and !first {/\D/} @e;
' file
10      2       12      1       13

Explanation

• s/^\s+|\s+$//g trim the line.

• @e = split /\s+/ split the line into array @e.

• We will print the line if:

  • array @e contains 5 or 6 elements.
  • And None of its elements contain non-digit characters (\D match non-digit characters).