Read a specific line from a file

say lines[6] // die "Short file";

Without an argument, the lines function reads filenames from the command line, or defaults to standard input. It then returns a lazy list, which we subscript to get the 7th element. Assuming this code is in a program called line7:

$ cal 2011 > cal.txt
$ line7 cal.txt
16 17 18 19 20 21 22  20 21 22 23 24 25 26  20 21 22 23 24 25 26  
$

This works even on infinite files because lists are lazy:

$ yes | line7
y
$