Task Automation with Batch File (.bat)

Batch file (.bat) can be easily written and used to excute repeated tasks at once. No special program is needed, but you can just use you favorite text editor or IDE to write some command and rename it to have .bat extension. Let’s review some commands you can use in writing your batch file.

echo

echo command is used in the syntax of echo [content to print]. This command outputs content trailing after echo on the command line. Let’s try writing a simple one.

echo Hello world

Let’s assume above file is named example.bat and placed in C:\user>. You can execute this batch file as follows.

C:\user>example.bat
C:\user>echo Hello world
Hello world

@echo off

In above example you can see that the command echo Hello world prints once and then the execution result Hello world follows. As your batch file size grows, outputing command itself can mess up your command prompt. If you add @echo off at some point of your batch file, commands after @echo off stops showing commands themselves but outputs print only.

(example.bat)

@echo off
echo Hello world

Above batch file outputs like:

C:\user>example.bat
Hello world

USE set to Handle Variables

You can even define custom variables and use them in your batch file with set command. set is used in set [variable]=[value] syntax and you can assign values to variables and use them afterwards. A trivial but important point is that there should be no spaces on both side of equal sign. So, using [variable] = [value] format violates desired syntax.

If you already declared using set and want to call it from other lines of a batch file, prepend and append % to the variable name.

(example.bat)

@echo off
set salute=Hello world
echo %salute%

Above file outputs as same with previous example.

C:\user>example.bat
Hello world

If a variable contains string, you can also format the output to print some of the characters only. The syntax is %[variable_name]:~[start_index],[output_length]%. If start_index is negative integer, starting index is spotted by counting inversly starting from the end of given string.

(example.bat)

@echo off
set salute=Hello world
echo %salute:~2,3%
echo %salute:~-3,3%

Output of executing above batch file results like below.

C:\user>example.bat
llo
rld

Using For Loop

Loop feature also is supported. For example, below loop scans all the files in current directory and prints filenames.

for %%i in (*) do echo %%i

In %%i, i is an arbitrarily given variable. So, below line does exactly same thing.

for %%f in (*) do echo %%f

In above examples, %%i or %%f is not just a string. It contains useful information as if it is some kind of object by itself. And you can elicit more information by adding some reserved keywords between %% and f.

For example, ~t is a reserved keyword for last modifed dates and you can print last modified dates for all the files using this.

for %%f in (*) do echo %%~tf

Similarly, ~x is for extensions and ~n is for filenames but extensions excluded.

Delayed Expansion

Now we got to know that for loop and custom variables can be used in batch file. Next natural question is whether we can use define custom variables and use them inside for loop.

For example, we already saw that below line prints all the filenames in current directory.

for %%i in (*) do echo %%i

Then intuitively, it seems reasonable to guess that below line works as same (we use parenthesis if more than one command follows after do statement).

for %%i in (*) do (
  set var=%%i
  echo %var%
)

However, in writing batch files, result of updating %var% is not reflected real-time when for loop is running. In above case, the output is printing same filename throughout the running for loop (guess which name prints - first file in directory? or last one?).

To prevent this the concept of Delayed Expansion is required. To enable this, we need to add setlocal EnableDelayedExpansion line and variables must be referred by ![variable name]! syntax rather than %[variable name]% syntax.

setlocal EnableDelayedExpansion
for %%i in (*) do (
  set var=%%i
  echo !var!
)

Passing External Parameters to Batch Files

We can pass one or more parameters when executing batch file and handle it inside of the batch file. For example, you can execute batch file like example.bat param1 param2 from command prompt. Inside batch file, passed parameters are sequentially named like %1, %2 or so. Let me give an example below.

(example.bat)

@echo off
echo Hello %1

If we run example.bat by passing additional parameters:

C:\user>example.bat world
Hello world

C:\user>example.bat waldo
Hello waldo

Passing multiple parameters is therefore also straightforward.

(example.bat)

@echo off
echo Hello! %1 %2 monring.

C:\user>example.bat Mighty fine
Hello! Mighty fine morning.

%0 has different use - to refer to the path of current .bat file.

Receiving User input

User input can be received using below format:

@ECHO OFF
SET STR =
SET /p STR="Enter any key: "
ECHO You entered %STR%

Store echo-ed Content into Clipboard

| CLIP command can be appended after using echo to copy the echoed contents into current clipboard buffer.

@ECHO OFF
SET STR =
SET /p STR="Enter any key: "
ECHO You entered %STR% and paste this sentence anywhere! | CLIP

Once you execute above batch file, you can paste “You entered banana and paste this sentence anywhere!” with ctrl+v

C:\user>example.bat banana
You entered banana and paste this sentence anywhere!

Calling A Batch File from Other One

You can also embed pre-built batch file in the other one using call keyword:

@ECHO OFF
echo I am an Apple!

@ECHO OFF
echo I am a Banana!
call apple.bat

Above banana.bat calls apple.bat inside of it.

C:\user>example.bat
I am a Banana!
I am an Apple!

Execute Batch File upon Booting

We can also use our batch file to define some routine jobs to be done upon booting Windows.

Locate Batch File in Startup Folder

• Use win+R command to pop up run dialog.
• Enter shell:startup and execute to open startup folder.
• Copy or move your batch file into startup folder.

Execute Python Code in Batch File

We can automatedly execute your python code in batch file.

<path of python.exe> <path of .py file>

For example,

"C:\Users\username\anaconda3\python.exe" "C:\myproject\mycode.py"

Execute Batch File in Python Code

You can also call your batch file in python code.

Using os

import os
os.startfile("example.bat")

Using subprocess

import subprocess
a = subprocess.Popen("example.bat")

If the location of example.bat is different from where above .py file is located, additional argument cwd is required.

import subprocess
cwd = f"C:\\examplefolder"
a = subprocess.Popen("example.bat", cwd=cwd)