[me@host bin]$ perl -we '$n = $ARGV[0]; $_ = "a b csadf sdfas ddd"; /(?:\S+\s+){@{[$n-1]}}(\S+)/; print "$1\n"' 1
a
[me@host bin]$ perl -we '$n = $ARGV[0]; $_ = "a b csadf sdfas ddd"; /(?:\S+\s+){@{[$n-1]}}(\S+)/; print "$1\n"' 2
b
[me@host bin]$ perl -we '$n = $ARGV[0]; $_ = "a b csadf sdfas ddd"; /(?:\S+\s+){@{[$n-1]}}(\S+)/; print "$1\n"' 4
sdfas
[me@host bin]$