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import subprocess

def bash_command(cmd):
   subprocess.Popen(cmd, shell=True, executable='/bin/bash')

bash_command('a="Apples and oranges" && echo "${a/oranges/grapes}"')
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Sortie:
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Apples and grapes
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OU si probleme:

------------------------------------------------------------------------------------------------
import subprocess

def bash_command(cmd):
   subprocess.Popen(['/bin/bash', '-c', cmd])
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Source 1:
http://www.saltycrane.com/blog/2011/04/how-use-bash-shell-python-subprocess-instead-binsh/
Source 2:
http://jimmyg.org/blog/2009/working-with-python-subprocess.html