Need to use a variable in an os.system command in

问题:

I am new to python and I need to use a variable in the os.system command, here's my code so far

import os , sys
s = raw_input('test>')

then i want to use the varable s in an os.system command so I was thinking something like os.system("shutdown -s -t 10 -c" 's')

I don't want answers for that specific command I just want to know in general but if you are going to use an example use shutdown

回答1:

then i want to use the varable s in an os.system

Use string.format function.

os.system("shutdown -s -t 10 -c {}".format(s))

回答2:

You can use os.system to execute the particular command, in which case you can join the two strings either by using the + operator, string formatting (.format()), string substitution or some other method.

However, consider the case when the user enters the command 5; rm -rf / or some other malicious command. Instead of using os.system you might want to take a look at subprocess

If you use subprocess you might find the following example handy:

import subprocess
s = raw_input('test>')
subprocess.call(["shutdown", "-s", "-t", "10", "-c", s])

回答3:

os.system takes a string as the argument, so you can use anything that modifies a string. For example, string formatting:

os.system('shutdown -s -t 10 -c {0}'.format(s))

回答4:

Use subprocess.check_call, pass a list of args and you can add the variable wherever you like:

from subprocess import check_call

check_call(["shutdown", some_var ,"-s", "-t" "10", "-c"])

回答5:

Passing place-holder "%s string alongside os.system" should work.

os.system() will execute the command in shell.

import os
var = raw_input('test>') # changed "s" variable to "var" to keep clean
os.system("shutdown -%s -t 10 -c", %(var)) # "var" will be passed to %s place holder

回答6:

os.system("shutdown -s -t 10 -c" + s)

1. The plus sign joins two strings
2. No quotes are used around s. That way you get the value the user entered and not just a literal "s".