> echo "abcd" | perl -nle '/(b).(d)/ && print "$1" '
b
> echo "abcd" | perl -nle '/(b).(d)/ && print "$2" '
d
> echo "abcd" | perl -nle '/(b).(d)/ && print "$1 $2" '
Can't open $2 : No such file or directory.

##</code><code>##

> echo "abcd" | perl -nle '/(b).(d)/ && print \`"$1 $2\`" '
Can't find string terminator "`" anywhere before EOF at -e line 1.