Why is whitespace sometimes needed around metacharacters?

A few months ago I tattooed a fork bomb on my arm, and I skipped the whitespaces, because I think it looks nicer without them. But to my dismay, sometimes (not always) when I run it in a shell it doesn't start a fork bomb, but it just gives a syntax error.

bash: syntax error near unexpected token `{:'

Yesterday it happened when I tried to run it in a friend's Bash shell, and then I added the whitespace and it suddenly worked, :(){ :|:& };: instead of :(){:|:&};:

Does the whitespace matter; have I tattooed a syntax error on my arm?!

It seems to always work in zsh, but not in Bash.

A related question does not explain anything about the whitespaces, which really is my question; Why is the whitespace needed for Bash to be able to parse it correctly?

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There is a list of characters that separate tokens in BASH. These characters are called metacharacters and they are | , & , ; , ( , ) , < , > , space and tab . On the other hand, curly braces ( { and } ) are just ordinary characters that make up words.

Omitting the second space before } will do, since & is a metacharacter. Therefore, your tattoo should have at least one space character.

:(){ :|:&};:

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Just tattoo a

#!/bin/zsh

shebang above it and you'll be fine.

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Braces are more like odd keywords than special symbols, and do need spaces. This is different to parentheses, for example. Compare:

(ls)

which works, and:

{ls}

which looks for a command named {ls} . To work, it has to be:

{ ls; }

The semicolon stops the closing brace being taken as a parameter to ls .

All you have to do is tell people that you are using a proportional-font with a rather narrow space character.

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