Python scripting in Linux
Contents
9. Python scripting in Linux¶
Jupyter notebook installation
Python libraries for interaction with Linux
Multiple account creation example
Sftp file transfer with python
9.1. Python programming environment: Jupyter notebook (Exercise)¶
Install python3-pip on your desktop:
sudo apt install python3-pip
Install Jupyter notebook on your desktop as user hostadm:
pip3 install notebook
Add the PATH environment variable in the bottom of .bashrc file in your home directory:
.bashrc
export PATH=$PATH:/home/hostadm/.local/bin
Source the .bashrc by running command:
source .bashrc
Assign the password to jupyter notes by running command:
jupyter notebook password
Create directory for python projects, and step into the directory:
mkdir Python
cd Python
Start jupyter notes by command below:
jupyter notebook &
Access jupyter notebook through the browser on your virtual desktop by navigating to URL below:
jupyter
http://localhost:8888
Start a new python3 project in the jupyter notebook.
9.2. Interaction with operating system¶
There are various python standard libraries utilized for interaction with the Linux environment, file systems, and processes.
We review only a few most commonly used:
os — Miscellaneous operating system interfaces
sys — System-specific parameters and functions
subprocess — Subprocess management
9.3. os — Miscellaneous operating system interfaces (Exercise)¶
In your Jupyter notebook, copy and paste the python code from the cell below:
#Current working directory
import os
os.getcwd()
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Try the following in the new cell:
#Change the directory
os.chdir("/etc")
os.getcwd()
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Try listing the files and directories in /etc:
# see the list of files and directories
os.listdir()
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Check if file hosts exists:
os.path.isfile("hosts")
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Check if file no_hosts exists:
os.path.isfile('no_hosts')
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Get the file system statistics on a file
os.stat('/etc/hosts')
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Get the directory path separator:
os.sep
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Generate the file names in a directory tree by walking the tree either top-down or bottom-up.
top='/etc'
for dirpath, dirnames, filenames in os.walk(top):
path = dirpath.split(os.sep)
print(path)
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Derive the directory path from a full path:
full_path="/etc/libvirt/qemu/kvm1.xml"
os.path.dirname(full_path)
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Create, rename, and remove directories:
os.chdir('/home/hostadm')
os.mkdir('DIR1')
os.rename('DIR1','DIR2')
os.rmdir('DIR2')
Execute a system command without controlling the stdout and stderr:
os.system('cd /etc; pwd')
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The output number is the last command error code.
9.4. Calling Linux commands from Python (Exercise)¶
The subprocess module allows you to spawn new processes, connect to their input/output/error pipes, and obtain their return codes. Example of class call
# Create directory DIR1 and check the disk usage in the directory
import subprocess
s=subprocess.run("mkdir DIR1; du -sh DIR1", shell=True)
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For full control of the standard input and the standart output to the command, we use class Popen:
import subprocess
s=subprocess.Popen("du -sh /etc", shell=True,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE,)
stdout_value,stderr_value = s.communicate()
print("std output=", stdout_value)
print("std error=", stderr_value)
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9.5. sys — System-specific parameters and functions (Exercise)¶
Identify the OS platform within Python:
import sys
sys.platform
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Example how it can be used:
if sys.platform.startswith('linux'):
# Linux-specific code here...
print('we are working in Linux environment')
else:
print('different OS')
Get the current PYTHONPATH:
import sys
print(sys.path)
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9.6. Scripts runnable from command line (Exercise)¶
The above scripts can be placed in a file, for example call.py:
#!/usr/bin/python3
# see the list of files and directories
import os
listf = os.listdir()
print(listf)
Make the file executable:
chmod a+x call.py
Run the script:
./call.py
9.7. Creating multiple user accounts with python (Exercise)¶
In directory Python, create a new file, users.txt, with editor nano:
users.txt:
mike 2000
jerry 2001
sam 2003
mary 2004
In jupyter notebook, run the following script:
import os
def user_cmd(user, uid, group, hdir):
s = f'useradd -m -d {hdir}/{user} -s /bin/bash -u {uid} -g {group} {user}'
return s
os.chdir('/home/hostadm/Python')
HDIR = '/NFS/home'
f = open('users.txt','r')
account = {}
for line in f:
key, value = line.rstrip().split()
account[key] = value
f.close()
for keys in account:
grp_cmd = f'groupadd -g {account[keys]} {keys}'
print(grp_cmd)
comm = user_cmd(keys, account[keys], account[keys], HDIR)
print(comm)
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Function print() above is a placeholder for function os.system() that would create accounts.
9.8. Transferring files with pysftp (Exercise)¶
On your desktop install pysftp:
pip3 install pysftp
Start run01 VM and find out its IP address:
virsh start run01
virsh domifaddr run01
For example, IP is 192.168.122.134
ssh to the VM to accept the public host key, and disconnect.
ssh 192.168.122.134
exit
In jupyter notebook, run the following steps to upload users.txt onto scripts VM.
Put the correct credentials into username and password:
import pysftp
with pysftp.Connection('192.168.122.134', username='...', password='...') as sftp:
sftp.put('/home/hostadm/Python/users.txt')
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9.9. Regular expressions (RE) for pattern search/replacement (Exercise)¶
Files can be read line by line into python lists. The lists can be searched for patterns.
Here we use re library with its methods.
Copy file list.txt from the shell scripting exercises into directory Python:
cd
cp bash_scripts/list.txt Python
Run the python script below to extract the lines containing “Reboot”, “reboot” or “support” strings
(aka grep -E '[Rr]eboot|support' list.txt command):
import re
f=open('list.txt','r')
for line in f:
match = re.search(r'[Rr]eboot|support', line)
if match:
print(line)
f.close()
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Substitute underscore for any number of spaces wherever they occur on the line (aka sed 's/ */_/g' list.txt):
import re
f=open('list.txt','r')
for line in f:
newline = re.sub(r' *', r'_', line)
print(newline)
f.close()
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9.10. Splitting lines into fileds (Exercise)¶
Display user names, home directories, and login shell (fields 1, 6 and 7) in /etc/passwd file.
Aka awk -F: '{ print $1, $6, $7 }' /etc/passwd command:
f=open('/etc/passwd','r')
for line in f:
f1,f2,f3,f4,f5,f6,f7 = line.split(':')
print(f1, f6, f7)
f.close()
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