CODEWITHSUNDEEP
bash
Uberhumus
Uberhumus

Reputation: 1178

Syntax error near unexpected token `;' when running a command in Bash

In Bash in the terminal, it is impossible to run a command that ends with and & (being sent to the background) followed by another command (obviously with a ; between them). Why is that? Why can't you run anything with &; or $ ; in it?

I'm trying to recreate a 502 error and was trying to DoS a specific page in a testing server. I was trying to run this:

while true; do curl -s https://some.site.com/someImage.jpg > /dev/null &; echo blah ; done

as a "one-liner" in the terminal. However, I got this error:

-bash: syntax error near unexpected token `;'

However the commands work individually, and when I run the curl command not in the background it works as a loop as well. It also works when it write a one line script, "/tmp/curlBack.sh" that includes only

curl -s https://some.site.com/someImage.jpg > /dev/null &

And then run

while true; do bash /tmp/curlBack.sh ; echo blah ; done

Why am I getting this error and how do I fix it?

Upvotes: 6

Views: 6086

Answers (1)

Mike Maazallahi
Mike Maazallahi

Reputation: 1289

The problem is with the semi-colon after the ampersand (&):

An ampersand does the same thing as a semicolon or newline in that it indicates the end of a command, but it causes Bash to execute the command asynchronously. BashSheet

Basically, it's as if you were to put double semi-colons back to back, that would cause a syntax error too.

To fix this problem, you simply need to remove the semi-colon, I tested it that way and it seems to be working:

while true; do curl -s https://some.site.com/someImage.jpg > /dev/null & echo blah ; done

Upvotes: 12

Related Questions