# lsof | grep TCP
portmap    2587   rpc  4u   IPv4     5544  TCP *:sunrpc (LISTEN)
rpc.statd  2606  root  6u   IPv4     5585  TCP *:668 (LISTEN)
sshd       2788  root  3u   IPv6     5991  TCP *:ssh (LISTEN)
sendmail   2843  root  4u   IPv4     6160  TCP badhd:smtp (LISTEN)
vsftpd     9337  root  3u   IPv4    34949  TCP *:ftp (LISTEN)
cupsd     16459  root  0u   IPv4    41061  TCP badhd:ipp (LISTEN)

Here’s a short list of useful Linux shell programs, many of which you may have never known about. I’ve got a new favorite shell command, lsof (shown above), which displays information on every open file handle. – Link.

If I could add one to the list, it’d have to be the short and sweet command line search and replace using perl:

perl -pi -e 's/searchpattern/replacewith/g' *.html

Do you have a favorite command line secret? Please share it in the comments.