bash "echo" including ">" in the middle creating file - please explain

Question

When I write:

echo 2*3>5 is a valid inequality

In my bash terminal, a new file named 5 is created in my directory which contains:

2*3 is a valid inequality

I want to know what exactly is going on here and why am I getting this output? I believe it's obvious that I'm new to Linux! Thanks

Answer 1

In bash, redirections can occur anywhere in the line (but you shouldn't do it! --- see the bash-hackers tutorial). Bash takes the >5 as a redirection, creates output file 5, and then processes the rest of the arguments. Therefore, echo 2*3 is a valid inequality happens, which gives you the output you see in the output file 5.

What you probably want is

echo "2*3>5 is a valid inequality"

or

echo '2*3>5 is a valid inequality'

(with single-quotes), either of which will give you the message you specify as a printout on the command line. The difference is that, within "", variables (such as $foo) will be filled in, but not within ''.

Edit: The bash man page says that the

redirection operators may precede or appear anywhere within a simple command or may follow a command. Redirections are processed in the order they appear, from left to right.

Answer 2

bash does the output redirection first i.e. >5 is done first and a file named 5 is created (or truncated if it already exists). The resultant file descriptor remains open for the runtime of the echo command.

Then the remaining portion, 2*3 is a valid inequality, runs as the argument to echo and standard output is saved in the (already-open) file 5 eventually.

To get the whole string as the output, use single or double quotes:

echo '2*3>5 is a valid inequality'