Altering my python path: helloworld.py returns command not found—
Let's start with the first error you received. Understanding error messages is important.
-bash: helloworld.py: command not found
This indicates that helloworld.py is not a command that can be executed. To run the file, you then have two options:
- Run it using the python interpreter.
python helloworld.py - Make the file executable and then run it directly.
./helloworld.py
To make files executable in a *nix environment, you have to change their mode to allow execution. In order to do this, you use the chmod command (man chmod for more info).
chmod +x helloworld.py
This assumes that you are in the directory containing the helloworld.py file. If not, cd there first or use the full path.
The ./ is necessary because it tells the shell to run the file located here, not by looking in $PATH. $PATH is a list of possible executable locations. When you try to run helloworld.py directly, the shell tries to look for it in $PATH. You want to run the local file, so you have to prefix it with ./, which means "from here".
As an aside, note the first line of your python script:
#!/usr/bin/python
This is called a shebang line and tells system to use the /usr/bin/python executable to load the file. Internally, that means that the program loader will be doing /user/bin/python helloworld.py.
Finally, when you called python with no arguments, you were dropped into an interactive Python interpreter session. >>> helloworld.py in this environment is not referencing the file of that name, it's just interpreted as python code. Invalid python code. This is why you get your second error, NameError: name 'helloworld' is not defined.
To turn a Python module or script into a standalone program on a UNIX system you have to do two things:
1.) Make sure you have the "shebang" in the top of your script:
#!/usr/bin/python
2.) Make sure the script file is executable. This is done using the chmod command:
chmod +x /path/to/helloworld.py
/path/to/ being the fully qualified file path to your script. If it's in the current directory, then you can omit the path.
% ls -l
total 0
drwxr-xr-x 2 jathan jathan 60 2011-04-13 15:28 ./
drwxrwxrwt 12 root root 6.5K 2011-04-13 15:28 ../
-rw-r--r-- 1 jathan jathan 0 2011-04-13 15:28 helloworld.py
It's in my current directory, so let's make it executable!
% chmod +x helloworld.py
% ls -l
drwxr-xr-x 2 jathan jathan 60 2011-04-13 15:28 ./
drwxrwxrwt 12 root root 6.5K 2011-04-13 15:28 ../
-rwxr-xr-x 1 jathan jathan 0 2011-04-13 15:28 helloworld.py*
See the "x"s in the permission bits on the left? You've done it! Now we can run it:
% ./helloworld.py
Hello World!
Lastly, never use semicolons as line-endings in Python. It's not required and it's ugly!
Wanted to add my 2 cents: Apart from permissions and path answers above, there is one more situation where you may still face the same error.
In-spite of correct permissions and the shebang header, you may still get the same "Command not found" error if you've originally written the file in Windows and copied it over to Linux. Due to differing line-ending characters, there will be extra '\r' characters on the lines.
This happens because there are non-printable characters in the file. Examing it by doing:
cat -v <filename>:
#!/usr/intel/bin/python^M
The extra "^M" is the problem. Use 'dos2unix' to convert the file and then it'll run fine.