redirection in a file with os.system

TP Tribulations at Paralleles.invalid
Mon Nov 3 20:06:02 CET 2008


Hi everybody,

The following code does not redirect the output of os.system("ls") in a
file:

import sys, os
saveout = sys.stdout
fd = open( 'toto', 'w' )
sys.stdout = fd
os.system( "ls" )
sys.stdout = saveout
fd.close()

Whereas the following works:

old_stdout = os.dup( sys.stdout.fileno() )
fd = os.open( 'bar', os.O_CREAT | os.O_WRONLY )
os.dup2( fd, sys.stdout.fileno() )
os.system( "ls" )
os.close( fd )
os.dup2( old_stdout, sys.stdout.fileno() )

Why?

I have another question: with this last code using os.open, the problem is
that the file 'bar' is not removed before being written. So, it could lead
to errors: the file 'bar' is overwritten, but extra lines from previous
executions could remain.
Am I compelled to use os.unlink (or os.remove) before calling
os.system("ls")?

Thanks

Julien

-- 
python -c "print ''.join([chr(154 - ord(c)) for c in '*9(9&(18%.9&1+,\'Z
(55l4('])"

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possible, he is almost certainly right. When he states that something is
impossible, he is very probably wrong." (first law of AC Clarke)



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