Why is `ls -al & ; ls -al` invalid?

Question

I ran this on my Centos5 box:

ls -al & ; ls -al

I was expecting it to run ls -al in the background, and concurrently run ls -al in the foreground, and demonstrate how the output to terminal gets all mangled by doing so.

However, I get:

-bash: syntax error near unexpected token `;'

How can I write these two commands on the same line?

Answer 1

Unintuitively, & is a command separator as well as a forker. That means you actually have three commands:

  ls -al & ; ls -al
# ^^^^^^^|^|^^^^^^^

... and Bash does not support the empty statement.

Instead, simply write:

  ls -al & ls -al

with no semicolon.