Under Unix-like operating systems you can either run scripts by specifying the interpreter along with the path python test.py, or you can run them as programs ./test.py, and have the interpreter specified in the shebang on the first line of the script.
Syntax
#! interpreter [optional-arg]
the script content run by the specified interpreter- The interpreter must be a valid pathname for an executable. Therefore something like
#!pythonwill not work becausepythonis not a path name. Use full path like#!/usr/bin/env python. - The interpreted usually takes only one argument, so you cannot do something like
#!/usr/bin/env node --harmony.
Example
#!/usr/bin/env bash
echo "Hello"usr/bin/env
Env is an executable in Unix-like operating systems that, among other things, is often used by shell scripts to launch the correct interpreter. Env is located at /usr/bin/env.
It is recommended to use #!/usr/bin/env instead of the absolute path like #!/usr/bin/python. Although #!/usr/bin/python will work on a default Ubuntu system, it is good practice to use #!/usr/bin/env python instead.
Same thing can be said about shells, you should use #!/usr/bin/env bash instead of #!/bin/bash for portability reasons. Different *nixes put the bash in various places, and using /usr/bin/env is a workaround to run the first bash found on the PATH.
Common shebangs
| Interpreter | Shebang |
|---|---|
| Bash | #!/usr/bin/env bash |
| Shell | #!/usr/bin/env sh |
| Python | #!/usr/bin/env python |
| Node.js | #!/usr/bin/env node |