What is the meaning of command “:() { :|:& }; :” in shell?

Question

I just encountered this command on a linux forum online where the author warned that donot try this command for curiosity. So my curiosity comes. What is the meaning of command “:() { :|:& }; :” in shell?

See [Fork bomb](http://en.wikipedia.org/wiki/Fork_bomb) for that is what it is. — Dan D., Aug 08 '14 at 09:37

score 7 · Accepted Answer · edited Mar 20 '17 at 10:04

This fork bomb is described here

In bash, a function can be defined

function_name() { ... }

where ... is the implementation or body of the function

:(){ ... }

defines a function named :.

:|:

runs the function within itself - that is recursively, and pipes it's output to another invocation of itself.

runs the preceding command in the background.

So that gives us :(){:|:&} to define this function

separates the command defining the function from the following command on the same line (like cd;pwd)

is a final command invocation which starts running the newly defined function.

Normally, I'd hope that per-user limits on processes or other resources would limit the effect of a fork bomb of this sort. Wikipedia has a description of defusing a fork bomb

Addendum: After writing this answer I noticed this question was a duplicate of

What is the meaning of command “:() { :|:& }; :” in shell?

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