python -c and `while`

Question

Is there a way to loop in while if you start the script with python -c? This doesn't seem to be related to platform or python version...

Linux

[mpenning@Hotcoffee ~]$ python -c "import os;while (True):    os.system('ls')"
  File "<string>", line 1
    import os;while (True):    os.system('ls')
                  ^
SyntaxError: invalid syntax
[mpenning@Hotcoffee ~]$
[mpenning@Hotcoffee ~]$ python -V
Python 2.6.6
[mpenning@Hotcoffee ~]$ uname -a
Linux Hotcoffee 2.6.32-5-amd64 #1 SMP Sun May 6 04:00:17 UTC 2012 x86_64 GNU/Linux
[mpenning@Hotcoffee ~]$

Windows

C:\Users\mike_pennington>python -c "import os;while True: os.system('dir')"
  File "<string>", line 1
    import os;while True: os.system('dir')
                  ^
SyntaxError: invalid syntax

C:\Users\mike_pennington>python -V
Python 2.7.2

C:\Users\mike_pennington>

I have tried removing parenthesis in the while statement, but nothing seems to make this run.

score 10 · Accepted Answer · answered Jun 27 '12 at 12:37

10

python -c $'import subprocess\nwhile True: subprocess.call(["ls"])'

would work (note the $'...' and the \n).

But it could be that it only works under bash - I am not sure...

answered Jun 27 '12 at 12:37

glglgl

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`os.system()` is obviously not canonical, but I've found that shorter questions are better on [so]. `os` is shorter than `subprocess` – Mike Pennington Jun 27 '12 at 12:46
If it was just supposed to be an example, `print 1234` (or `print(1234)`) would have been enough as well. But that's not the main pont of this all... – glglgl Jun 27 '12 at 13:10

score 5 · Answer 2 · edited Jun 27 '12 at 12:36

5

Multiline statements may not start after a statement-separating ; in Python – otherwise, there might be ambiguities about the code blocks. Simply use line breaks in stead of ;. This "works" on Linux:

$ python -c "import os
while True: os.system('ls')"

Not sure how to enter this on Windows, but why not simply write the commands to a .py file if it's more than one line?

edited Jun 27 '12 at 12:36

unkulunkulu

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answered Jun 27 '12 at 12:34

Sven Marnach

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@MikePennington: If it's a one-time use, why don't you launch the interpreter and enter the commands there? – Sven Marnach Jun 27 '12 at 12:46
shell redirection and pipes, somewhat easier `bash` up-arrow editing if I make a mistake... and I'm still hooked on `perl -e` syntax from years of perl usage – Mike Pennington Jun 27 '12 at 13:06

score 2 · Answer 3 · answered Jun 27 '12 at 12:34

2

Don't know about windows, if all you want is to be able to type in one-liners, you could consider line breaks inside quotes:

% python -c "import os;
while (True):
  os.system('ls')"

answered Jun 27 '12 at 12:34

unkulunkulu

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score 2 · Answer 4 · answered Jun 27 '12 at 12:48

2

If you really must do this in windows, you could use exec:

python -c "exec \"import os;\rwhile True:\r  os.system('dir')\""

(I substituted dir so it works on my windows system)

answered Jun 27 '12 at 12:48

Gerrat

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python -c and `while`

4 Answers4