What's this?

commandlinefu.com is the place to record those command-line gems that you return to again and again.

Delete that bloated snippets file you've been using and share your personal repository with the world. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.

If you have a new feature suggestion or find a bug, please get in touch via http://commandlinefu.uservoice.com/

Get involved!

You can sign-in using OpenID credentials, or register a traditional username and password.

First-time OpenID users will be automatically assigned a username which can be changed after signing in.

Universal configuration monitoring and system of record for IT.

Stay in the loop…

Follow the Tweets.

Every new command is wrapped in a tweet and posted to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning, there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.

» http://twitter.com/commandlinefu
» http://twitter.com/commandlinefu3
» http://twitter.com/commandlinefu10

Subscribe to the feeds.

Use your favourite RSS aggregator to stay in touch with the latest commands. There are feeds mirroring the 3 Twitter streams as well as for virtually every other subset (users, tags, functions,…):

Subscribe to the feed for:



2011-03-12 - Confoo 2011 presentation
Slides are available from the commandlinefu presentation at Confoo 2011: http://presentations.codeinthehole.com/confoo2011/
2011-01-04 - Moderation now required for new commands
To try and put and end to the spamming, new commands require moderation before they will appear on the site.
2010-12-27 - Apologies for not banning the trolls sooner
Have been away from the interwebs over Christmas. Will be more vigilant henceforth.
2010-09-24 - OAuth and pagination problems fixed
Apologies for the delay in getting Twitter's OAuth supported. Annoying pagination gremlin also fixed.

Top Tags



create random string from /dev/urandom (or another length)

Terminal - create random string from /dev/urandom (or another length)
echo `cat /dev/urandom |tr -dc "[:alnum:]" | head -c64`
2010-12-06 20:01:56
Functions: echo head tr
create random string from /dev/urandom (or another length)


There is 1 alternative - vote for the best!

Terminal - Alternatives
echo `cat /dev/urandom | base64 | tr -dc "[:alnum:]" | head -c64`
2010-12-06 21:04:57
User: Dereckson
Functions: echo head tr

The same command, but with a base64 filter, more forgiving for special characters than tr.

Know a better way?

If you can do better, submit your command here.

What others think

On FreeBSD 8.1:

tr: Illegal byte sequence

Comment by Dereckson 229 weeks ago

That cat's not necessary:

echo $(</dev/urandom tr -dc "[:alnum:]" | head -c64)
Comment by eightmillion 229 weeks ago

Your variant works only with sh, zsh and bash eightmillion.

In tcsh, you'll got "Illegal variable name." as output

By the way, head -c doesn't work on OpenBSD.

Comment by Dereckson 228 weeks and 6 days ago

It works on ash, dash, bash, sh, ksh, zsh, and sash. The only reason it doesn't work on csh variants is because they aren't posix compliant with respect to command substitution. Try:

echo `</dev/urandom tr -dc "[:alnum:]" | head -c64`
Comment by eightmillion 228 weeks and 6 days ago

Thanks for all your comments. This is my "greeting" command. Maybe another version will be later. I test and use it in my gentoo linux box with bash.

I agree that echo not needed. Its just cosmetics.

Comment by unixmonkey14859 228 weeks and 4 days ago

Your point of view

You must be signed in to comment.