perl grep (like unix's grep utility) - example args: '^[Cc]hris[^:]*' /etc/passwd

perl -we'$;=shift;die+grep{/$;/}<>'

portscanner

perl -MIO::Socket -wle'map { IO::Socket::INET->new(qq($ARGV[0]:$_)) and print } 1..$ARGV[1]||10000' localhost 1000

portscanner #2 (tells you which service runs on each open port)

perl -MIO::Socket -le'open S, "/etc/services" or die $!; /^(\S+)\s+(\d+)/ and $s{$2}=$1 for <S>;
IO::Socket::INET->new("$ARGV[0]:$_") and print "$s{$_}($_)" for 1..$ARGV[1]||1024' localhost 2000

Fetch a webpage (text-mode)

perl -MLWP::Simple -wlegetprint+pop 'http://site.com'

Generate random alphanumerical string (password generator)

perl -le'print map { (a..z,A..Z,0..9)[rand 62] } 0..pop' 7

Generate string using most characters (on my keyboard :-) )

perl -le'print map { chr( rand(93) +33 ) } 0..pop' 7

Stat your mbox (or logfile) for changes

perl -wle'$s = sub {(stat($ARGV[0]))[9]}; $t = &$s; for (;;) { sleep 2;
if ( &$s > $t) { $t = &$s; print "you have mail" } }' /var/mail/chris

Remove last character of each line of a file (or files!) and make backups of modified files.

perl -i.bk -wpe'chop' file

Ever watch a BSD box boot?

perl -e'$|++; 1 while select("","","",.04), print "\b", qw(/ - \ |)[$i++%4]'

Have a better/similar/smaller solution? E-mail me the one liner and I will put it up (and give you credit).