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Python script mysteriously refuses to run on Unix


Introduction

I was writing a new Python script (actually, a replacement for a bash script) at work today. I have a Windows laptop at work and in my projects and I often do development on Windows but the real objective is for the scripts and other work to run in a Unix system running under VirtualBox and Vagrant. To be exact, the system is: 
Ubuntu 14.04.5 LTS (GNU/Linux 3.13.0-143-generic x86_64)

Anyway, I was writing away and it worked ok up to a point on Windows but it needed resources on the Unix system so you might say it failed miserably but I was ready to try it on the virtual machine. When I tried, I got: 
(venv) vagrant@vagrant-host:/vagrant$ bruno/foobar.py --foo
: No such file or directory
(venv) vagrant@vagrant-host:/vagrant$

What the hell? That's a terrible error message. As an aside, I think some Python error messages can be awful and don't do a good job at fixing the problem. I think Python is a superb language but its error messages are not always the best.
Anyway, the error looked familiar but I couldn't remember what was wrong or how to fix it right off the bat. Some other facts:
  • The script uses #! /usr/bin/env python because the virtual machine has a newer version of Python in the $PATH which is supposed to override the system Python and I wanted to make use of it.
  • The script works fine if I do type python bruno/foobar.py --foo from the virtual machine command line but I don't want to have to do that.
  • I created the script on Windows using gvim
  • Remember, the script works fine from Windows!

Long story, short

After battling with this for several minutes, it finally dawned on me that I could be a poor victim of the Curse of the Carriage Return! When you create files on Windows, the file often has a carriage return character the precedes every newline character. Windows notepad is notorious for that - not only does it use carriage returns when you save a file but if you try to open a file that doesn't have carriage returns, it kind of acts like there are no newlines at all. Sometimes this can cause problems if you try to use the file in Unix or you might see funny symbols when you edit the file. There might be an option to not do that with gvim - I'll have to check that out.

I have a script called nocrs that can remove carriage returns on a file. Using that fixed up my script! Gosh, I just realized it's a bash script but that's ok with me.

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Comments

  1. John (aka Bruno)February 26, 2019 at 8:47 AM

    Recently I went back and rewrote my nocrs script as Python. I think I might have even made use of the logging and argparse modules. I've been loving using those lately.

    ReplyDelete

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