Executing system commands in python is helpful to automate repetitive system tasks such as file backup or health checks.
You can execute system commands from Python using subprocess.run([command]).
There are also other methods available to execute system commands from Python.
If you’re in Hurry
You can use the code snippet below to call a system command from Python.
Snippet
import subprocess
result = subprocess.run(['dir', 'F:\Writing\Files'], stdout=subprocess.PIPE, shell=True, text=True)
result.stdout
Output
Volume in drive F is New Volume
Volume Serial Number is 7CE4-C7CB
Directory of F:\\Writing\\Files
27-10-21 19:33 <DIR> .
27-10-21 19:33 <DIR> ..
27-10-21 19:33 335,042 commons-codec-1.11.jar
27-10-21 19:33 61,829 commons-logging-1.2.jar
4 File(s) 1,904,795 bytes
4 Dir(s) 50,031,755,264 bytes free'If You Want to Understand Details, Read on…
This tutorial will teach you the different methods to execute a system command from Python.
Table of Contents
Command Example
You’ll execute the Dir command in windows or ls command in Linux OS to list the folders and files in the directory for demonstration.
Dir Command in Windows
If you’re using Windows operating system, use the Dir command to list all the files and folders in the directory. It also accepts optional parameters to customise the output.
c:\users\stackvidhya > dirOutput
All the files and folders in the directory stackvidhya will be listed.Ls Command in Linux
If you’re using a Unix-like operating system, use ls to list all the files and folders in the directory. It also accepts optional parameters to customise the output.
$ ls Output
All the files and folders in the current directory will be listed.Now, you’ll see how to execute the system or shell commands from Python using different options.
Using Subprocess.run
You can use the run() method in Subprocess to execute a shell command from Python. It is available in Python by default.
It executes the command as described in the arguments. It accepts one mandatory parameter as a list. As explained below, any additional arguments to the shell command itself can be added as a list item.
['dir', 'F:\Writing\Files']– Python list wherediris the shell command and'F:\Writing\Files'is the additional argument todircommand to list the files in that specific directory.stdout=subprocess.PIPE–Optional. To capture the command output.shell=True–Optional. To execute the command over Python shell. This will be useful if you use Python just to execute the shell command for the enhanced control flow that Python offers over most system shells. Read the Security Considerations before usingshell=True.text=True– Optional. To encode stdin, stdout and stderr as text objects instead of binary streams.
Use the following command to execute the shell command dir and print the output in the console.
Snippet
import subprocess
result = subprocess.run(['dir', 'F:\Writing\Files'], stdout=subprocess.PIPE, shell=True, text=True)
result.stdoutYou’ll see the details of files and folders available in the directory, as shown below.
Output
Volume in drive F is New Volume
Volume Serial Number is 7CE4-C7CB
Directory of F:\\Writing\\Files
27-10-21 19:33 <DIR> .
27-10-21 19:33 <DIR> ..
27-10-21 19:33 335,042 commons-codec-1.11.jar
27-10-21 19:33 61,829 commons-logging-1.2.jar
4 File(s) 1,904,795 bytes
4 Dir(s) 50,031,755,264 bytes free'This is how you can call a shell command using subprocess.run().
Using Subprocess.popen
You can also use the popen constructor and communicate() method in Subprocess to execute a shell command from Python. It is available in Python by default.
Popen constructor accepts the same parameters as the run method.
After creating the Popen object, you should invoke the communicate() method, and it returns the tuple that consists stdout (Output messages) and stderr (error messages).
The messages are available in byte mode. Use the decode() method to decode it to String.
Snippet
import subprocess
p = subprocess.Popen(['dir', 'F:\Writing\Files'], shell=True, stdout=subprocess.PIPE)
stdout, stderr = p.communicate()
stdout.decode()
Output
Volume in drive F is New Volume
Volume Serial Number is 7CE4-C7CB
Directory of F:\\Writing\\Files
27-10-21 19:33 <DIR> .
27-10-21 19:33 <DIR> ..
27-10-21 19:33 335,042 commons-codec-1.11.jar
27-10-21 19:33 61,829 commons-logging-1.2.jar
4 File(s) 1,904,795 bytes
4 Dir(s) 50,031,755,264 bytes free'This is how you can use the popen class, and the communicate() method to execute a shell command in Python.
Using OS.System
OS module helps interact with the operating systems. Be it Linux or Windows.
System command in the OS module helps you execute the command in the subshell.
Use the below code to execute a shell command using the os.system() method.
Snippet
import os
home_dir = os.system("cd ~")
print("`cd ~` ran with exit code %d" % home_dir)
unknown_dir = os.system("cd doesnotexist")
print("`cd doesnotexis` ran with exit code %d" % unknown_dir)Output
`cd ~` ran with exit code 1
`cd doesnotexis` ran with exit code 1This is how you can use the os.system command to execute the shell command.
Execute Shell Command and Get Output
Get output While using Subprocess.RUN
The following code demonstrates how to execute a system command and get output while using the subprocess.run().
Snippet
import subprocess
result = subprocess.run(['dir', 'F:\Writing\Files'], stdout=subprocess.PIPE, shell=True, text=True)
result.stdoutOutput
Volume in drive F is New Volume
Volume Serial Number is 7CE4-C7CB
Directory of F:\\Writing\\Files
27-10-21 19:33 <DIR> .
27-10-21 19:33 <DIR> ..
27-10-21 19:33 335,042 commons-codec-1.11.jar
27-10-21 19:33 61,829 commons-logging-1.2.jar
4 File(s) 1,904,795 bytes
4 Dir(s) 50,031,755,264 bytes free'Get output While using Subprocess.Popen
The following code demonstrates how to execute a system command and get output while using the subprocess.Popen().communicate().
import subprocess
p = subprocess.Popen(['dir', 'F:\Writing\Files'], shell=True, stdout=subprocess.PIPE)
stdout, stderr = p.communicate()
stdout.decode()
Output
Volume in drive F is New Volume
Volume Serial Number is 7CE4-C7CB
Directory of F:\\Writing\\Files
27-10-21 19:33 <DIR> .
27-10-21 19:33 <DIR> ..
27-10-21 19:33 335,042 commons-codec-1.11.jar
27-10-21 19:33 61,829 commons-logging-1.2.jar
4 File(s) 1,904,795 bytes
4 Dir(s) 50,031,755,264 bytes free'Execute Shell Command and Get Error
Get Error While using Subprocess.RUN
The following code demonstrates how to execute a shell command and get errors using the subprocess.run().
In this example, the directory is not existing. hence you’ll see the output File Not Found
import subprocess
result = subprocess.run(['dir', 'F:\Writing\Filess'], stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=True, text=True)
result.stderr
Output
'File Not Found\n'Get Error While using Subprocess.Popen
The following code demonstrates how to execute a system command and get errors using the subprocess.Popen().communicate().
In this example, the directory is not existing. Hence you’ll see the output of File Not Found message.
Snippet
import subprocess
result = subprocess.Popen(['dir', 'F:\Writing\Filess'], shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True)
stdout, stderr = result.communicate()
stderrOutput
'File Not Found\n'This is how you can get output messages and error messages while executing system commands in Python.
Run Shell Script With Arguments
This section will teach you how to pass arguments while running a shell script from Python.
The arguments can be passed as additional items in the command’s list parameter.
For example, If you want to list only the directories in a folder using the dir command in Windows, you can do it with the additional argument /aD. Add this argument as an additional list item and pass the list to subprocess.run(). It will execute with the shell command with additional arguments appropriately.
Snippet
import subprocess
result = subprocess.run(['dir', 'F:\Writing\Files', '/aD'], capture_output=True, shell=True)
print(result.stdout.decode())Only the directories in the folder F:\Writing\Files are listed below.
Output
Volume in drive F is New Volume
Volume Serial Number is 7CE4-C7CB
Directory of F:\Writing\Files
27-10-21 19:33 <DIR> .
27-10-21 19:33 <DIR> ..
27-10-21 19:31 <DIR> src
27-10-21 19:23 <DIR> Web-Pagination-Finder-master
0 File(s) 0 bytes
4 Dir(s) 50,031,755,264 bytes freeThis is how you can pass arguments to shell commands while running from Python.
Run Multiple Commands at Once
In this section, you’ll learn how to run multiple shell commands at once from Python.
In windows: You can use the & operator to concatenate two commands.
In Linux: You can use the | operator to concatenate two commands.
For example, you’ll use two commands dir F:\Writing\Files and echo 'All the files and folders are listed'
The first command will list the files and folders in the directory, and the second command will print the output All the files and folders are listed.
Snippet
import subprocess
command = "dir F:\Writing\Files & echo 'All the files and folders are listed'"
result= subprocess.run(command, stdout=subprocess.PIPE, shell=True)
print(result.stdout.decode())Output
Volume in drive F is New Volume
Volume Serial Number is 7CE4-C7CB
Directory of F:\\Writing\\Files
27-10-21 19:33 <DIR> .
27-10-21 19:33 <DIR> ..
27-10-21 19:33 335,042 commons-codec-1.11.jar
27-10-21 19:33 61,829 commons-logging-1.2.jar
4 File(s) 1,904,795 bytes
4 Dir(s) 50,031,755,264 bytes free'
'All the files and folders are listed'Conclusion
To summarise, you’ve learned how to execute a shell command in Python.
Also, you’ve learned how to pass arguments, run multiple shell commands at once, and get the output and error messages while calling shell commands from Python.
If you’ve any questions, comment below.