UPDATE: I rewrote the whole script. You can find it here!

I wanted to get into Python recently and to have a reason to actually learn the language, I thought to myself, why not replace the bash-scripts I use on my private computer. I started with my backup script, that saves my home-folder to my external usb-drive.

With this article I’ll describe what I did and why. I’ll have some thoughts in my mind on what the script should do. You’ll see these below. Afterwards I’ll show how I accomplished these things.

Preliminary considerations

  • It should check if the directories actually exist.
  • It should ask for confirmation before doing anything
  • I needed the script to backup the specified folder to the specified location.
  • It should delete unnecessary files before backing up
  • Considering I used rsync in my bash-script I wanted the same functionality again

Writing the script

Check if directory exists

Python actually already has a function that checks if a directory exists: os.path.exists

So all I had to do was to use the built-in function and put it in my own little function, that performs the checks and prints an error-message and exits, if the directory does not exist.

def check_dir_exist(os_dir):
if not os.path.exists(os_dir):
print os_dir, "does not exist."
exit(1)

Confirm on actions

I wanted to let the user confirm any actions he does before they are executed, so he or she can back out if there was a mistake.

For that I built a function that asks for confirmation and if the answer is “yes”, the variable “exit_condition” should be 0, otherwise it is 1. So when the function is executed, depending on what status the variable took, I can decide on how to continue in the script.

def confirm():  
    gogo = raw_input("Continue? yes/no\n")  
    global exit_condition  
    if gogo == 'yes':  
        exit_condition = 0  
        return exit_condition  
    elif gogo == "no":  
        exit_condition = 1  
        return exit_condition  
    else:  
    print "Please answer with yes or no."  
confirm()

Defining backup paths

This one’s simple. The script just asks for user input on the paths for what to backup and where to put it. Afterwards there’s the existence-check.

# Specify what and where to backup.  
backup_path = raw_input("What should be backed up today?\n")
check_dir_exist(backup_path)
print "Okay", backup_path, "will be saved."  
time.sleep(3)  
backup_to_path = raw_input("Where to backup?\n")  
check_dir_exist(backup_to_path)

Delete files

I wanted to delete unecessary files like temporary or backup files before doing the backup. For this I created to functions. The first functions takes an argument (in this case: file endings) as input and searches in the backup path for files ending with the argument. It then deletes these files.

def delete_files(ending):
    os.chdir(backup_path)
    for r, d, f in os.walk(backup_path):
        for files in f:
            if files.endswith("." + ending):
                os.remove(os.path.join(r, files))

I use this function in a for-loop that iterates trough three file endings, each time asking the user if he/she wants to delete the files.

# Delete files first
print "First, let's cleanup unnecessary files in the backup path."
file_types = ["tmp", "bak", "dmp"]
for file_type in file_types:
    print "Delete", file_type, "files?"
    confirm()
    if exit_condition == 0:
        delete_files(file_type)

At last, the trash can of the user executing the script gets deleted. I uses shutil.rmtree for this. It deletes the whole file-directory. Don’t worry: it’s recreated when a file is moved to the trash. os.path.expanduser just expands the “~” to the user’s home directory.

# Empty trash can
print "Empty trash can?"
confirm()
if exit_condition == 0:
    print "Emptying!"
    shutil.rmtree(os.path.expanduser("~/.local/share/Trash/files"))

Backing up the files

This is the important part of the script. I tried to find an rsync alternative in Python, I searched for a method to mimic the rsync behaviour but I didn’t find anything that was easy to understand, capable of what it should do and not outdated. That is, until I found Rsyncbackup a Python script “to perform automatic backups using the rsync command”. It does exactly what it says it does, so I went on and used it in my script.

So I used rsync itself in combination with sh. Sh let’s me execute any program as if it were python native.

rsync("-auhv", "--delete", "--exclude=lost+found", "--exclude=/sys", "--exclude=/tmp", "--exclude=/proc",
  "--exclude=/mnt", "--exclude=/dev", "--exclude=/backup", backup_path, backup_to_path)

The result

Here’s the whole script put together:

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#!/usr/bin/env python

import os
import shutil
import time

from sh import rsync

# Functions

def check_dir_exist(os_dir):
    if not os.path.exists(os_dir):
        print os_dir, "does not exist."
        exit(1)

def confirm():
    gogo = raw_input("Continue? yes/no\n")
    global exit_condition
    if gogo == 'yes':
        exit_condition = 0
        return exit_condition
    elif gogo == "no":
        exit_condition = 1
        return exit_condition
    else:
        print "Please answer with yes or no."
        confirm()

def delete_files(ending):
    for r, d, f in os.walk(backup_path):
        for files in f:
            if files.endswith("." + ending):
                os.remove(os.path.join(r, files))

# Specify what and where to backup.
backup_path = raw_input("What should be backed up today?\n")
check_dir_exist(backup_path)
print "Okay", backup_path, "will be saved."
time.sleep(3)

backup_to_path = raw_input("Where to backup?\n")
check_dir_exist(backup_to_path)

# Delete files first
print "First, let's cleanup unnecessary files in the backup path."
file_types = ["tmp", "bak", "dmp"]
for file_type in file_types:
    print "Delete", file_type, "files?"
    confirm()
    if exit_condition == 0:
        delete_files(file_type)

# Empty trash can
print "Empty trash can?"
confirm()
if exit_condition == 0:
    print "Emptying!"
    shutil.rmtree(os.path.expanduser("~/.local/share/Trash/files"))

# Do the actual backup
print "Doing the backup now!"
confirm()
if exit_condition == 1:
        print "Aborting!"
        exit(1)

rsync("-auhv", "--delete", "--exclude=lost+found", "--exclude=/sys", "--exclude=/tmp", "--exclude=/proc",
  "--exclude=/mnt", "--exclude=/dev", "--exclude=/backup", backup_path, backup_to_path)

Releasing

Since this was my first python-project I thought to myself that i need to package and distribute it. Even if it’s only one file, I did it just for the sake of it.

So here it is, have fun with it on GitHub.

Plans

I plan on adding several things to it, as I progress in learning Python:

  • extensive Logging (I know, the Rsyncbackup already does logging, but I want the whole script to log)
  • Automatization
  • Develop my own Rsyncbackup - alternative


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