Why do you need to put #!/bin/bash at the beginning of a script file?

Question

I have made [Bash][1] scripts before and they all ran fine without this at the beginning. What's the point of putting it in? Would things be any different? Also, how do you pronounce `#`? I know that `!` is pronounced as "bang." How is `#!` pronounced? [1]: http://en.wikipedia.org/wiki/Bash_%28Unix_shell%29

Answer 1

There are several questions here. I'll try to answer them sequentially.

How do you pronounce #? I know that ! is pronounced as "bang." How is #! pronounced?

The symbol # is pronounced as "hash" and together with !(bang), the sequence #! is pronounced as hashbang or shebang.

What's the point of putting it in? Would things be any different?

When we put the #! symbol at the beginning of an executable file, the shell will recognize the interpreter it needs to invoke to execute the file with. For example:

Putting "#!/bin/bash" at the beginning of some file "script" and executing the file with "./script", will execute the file on /bin/bash interpreter. Similarly, if we change the shebang to "#!/bin/python" and try to execute it by running "./script", the shell will try to execute it with the /bin/python interpreter.

Removing the shebang would require us to execute it with "/bin/bash script" or "/bin/python script".