How to get the shebang line to work in python scripts ?

pascor · 07-08-2012, 08:24 PM

As an Linux/Ubuntu (12.04) newbie I can't figure out the combination of requirements to be able to use the shebang (#!/usr/bin/python) on line #1 to get the file to be interpreted by the python interpreter:

- Does the .py file have to be marked executible ?
- Does the .py file have to be in $PATH ?
- Does any particular shell have to run the py file ?
- Do any extra python environment variables have to be defined ?
- Will I simply only have to type "mypyfile.py <Enter>" at the command line to get the script run when things are set up properly ?

TIA

TobiSGD · 07-08-2012, 08:39 PM

If you just want to type the name of your script to run it there are some requirements for that:
1. The file must be executable.
2. The file must be in the $PATH. That means on most distros that you have to prefix the the name with ./ if you are in the same directory as the script.
3. The shebang must be correct. While

Code:

#!/usr/bin/python

may work it is better to use

Code:

#!/usr/bin/env python

pascor · 07-08-2012, 09:21 PM

Nope ! I'm using Ubuntu 12.04 LTE :

$ PATH="$PATH:/home/mack/Desktop/FINDFILE"
$ echo $PATH
/usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/home/mack/Desktop/FINDFILE
$
$ ll *.py
-rwxr-xr-x 1 mack mack 15522 Jul 8 21:14 findfile.py*
$
$ ./findfile.py
: No such file or directory

What gives ?!

TobiSGD · 07-08-2012, 09:32 PM

Can't say, works here and on any other Linux system I own:

Code:

tobi@dragon ~ :) % cat test.py
#!/usr/bin/env python

print "Hello World!"
tobi@dragon ~ :) % ls -l test.py
-rwxr-xr-x 1 tobi users 44 Jul  9 03:30 test.py
tobi@dragon ~ :) % ./test.py
Hello World!
tobi@dragon ~ :) %

pascor · 07-08-2012, 11:56 PM

The mystery thickens :

$ ls -l *.py
-rwxrwxr-x 1 mack mack 15522 Jul 8 22:33 findfile.py
-rwxrwxr-x 1 mack mack 44 Jul 8 22:32 test.py
$
$ ./test.py
Hello World!
$
$ ./findfile.py
: No such file or directory
$
$ cp findfile.py abc.py
$
$ chmod 775 abc.py
$ ./abc.py
: No such file or directory
$
$ cp test.py abc.py
$ ./abc.py
Hello World!
$

---------------------------------------

I edited file abc.py and replaced it's original content with that of file findfile.py :

---------------------------------------

$ ./abc.py

$ isFrozen : False
+ SCRIPT_ROOT : /home/mack/Desktop/FINDFILE/./abc.py
$ sys.executable : /usr/bin/python
$ sys.prefix : /usr
$ sys.argv : ['./abc.py']

./abc.py usage :
$ python ./abc.py [ options ] filename [, file ...] [ dir [, dir ...] ]

---------------------------------------

File abc.py now works as expected !

THE REASON:

The EOL marker from MSW-created text files is confusing Ubuntu.

THE FIX:

Run utility sed on the MSW-created-text-file-copied-to-Ubuntu as follows :

$ sed -i 's/\r//g' {filename}

----

BTW: Kate does not convert files with "\n\r" EOL markers even though it is set to save in posix EOL format. Character "\r" is an illegal character in posix text files.

----

I'm very surprised and saddened this thread didn't produce a dozen+ replies suggesting doing something like this.

TobiSGD · 07-09-2012, 12:34 AM

I am not using Windows for coding and I assume many people here don't also. So something like that can be easily forgotten.

chrism01 · 07-09-2012, 08:11 PM

@OP: you'd be amazed how many different ways you can screw up a file ...
Anyway, as above all the experienced guys find it easier/quicker to edit direct on *nix anyway.
If you had mentioned you created it on MSW, that would have been the first reply

Anyway, there is a tool to do this properly http://linux.die.net/man/1/dos2unix and reverse http://linux.die.net/man/1/unix2dos.
NB: on some other Unix systems its unixtodos, dostounix.