How to force os.system() to use bash instead of shell

Question

I've tried what's told in How to force /bin/bash interpreter for oneliners

By doing

os.system('GREPDB="my command"')
os.system('/bin/bash -c \'$GREPDB\'')

However no luck, unfortunately I need to run this command with bash and subp isn't an option in this environment, I'm limited to python 2.4. Any suggestions to get me in the right direction?

Mesothorax

Why the subprocess module is not an option? It is supported in Python 2.4. – Vassaux

pretty sure it is in 2.4.6, however this is 2.4.3 – Mesothorax

What about one of the various exec* functions? – Trimeter

Putting a shell command in a shell variable is almost always completely the wrong thing to do. – Fourchette

Answer 1

Both commands are executed in different subshells.

Setting variables in the first system call does not affect the second system call.

You need to put two command in one string (combining them with ;).

>>> import os
>>> os.system('GREPDB="echo 123"; /bin/bash -c "$GREPDB"')
123
0

NOTE You need to use "$GREPDB" instead of '$GREPDBS'. Otherwise it is interpreted literally instead of being expanded.

If you can use subprocess:

>>> import subprocess
>>> subprocess.call('/bin/bash -c "$GREPDB"', shell=True,
...                 env={'GREPDB': 'echo 123'})
123
0

Vassaux

unfortunately this is still giving me shell errors :-( – Mesothorax

@0n35, Could you post the traceback ? – Vassaux

Answer 2

The solution below still initially invokes a shell, but it switches to bash for the command you are trying to execute:

os.system('/bin/bash -c "echo hello world"')

Allergen

Answer 3

I use this:

subprocess.call(["bash","-c",cmd])

//OK, ignore this because I have not notice subprocess not considered.

Whose

Please explain a little more. How does it work? Why is it a workaround? – Chthonian

@Chthonian actually it is a workaround to fix my issue in windows msysgit environment. – Whose

Answer 4

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

Chuddar

Popen merely starts a process; you should manage the resulting object yourself. Of course, you can just use subprocess.run() instead, which does all of this plumbing for you. – Fourchette

Answer 5

I searched this command for some days and found really working code:

import subprocess

def bash_command(cmd):
    subprocess.Popen(['/bin/bash', '-c', cmd])

code="abcde"
// you can use echo options such as -e
bash_command('echo -ne "'+code+'"')

Output:

abcde

Placentation

echo in particular isn't a very good example; you should prefer printf. Though I suppose this would work if your specific question was "how can I use Bash's built-in echo from Python?" – Fourchette