Batch Script - Quick Guide

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Batch Script - Overview

Batch Script is incorporated to automate command sequences which are repetitive in nature. Scripting is a way by which one can alleviate this necessity by automating these command sequences in order to make one’s life at the shell easier and more productive. In most organizations, Batch Script is incorporated in some way or the other to automate stuff.

Some of the features of Batch Script are −

• Can read inputs from users so that it can be processed further.

• Has control structures such as for, if, while, switch for better automating and scripting.

• Supports advanced features such as Functions and Arrays.

• Supports regular expressions.

• Can include other programming codes such as Perl.

Some of the common uses of Batch Script are −

• Setting up servers for different purposes.

• Automating housekeeping activities such as deleting unwanted files or log files.

• Automating the deployment of applications from one environment to another.

• Installing programs on various machines at once.

Batch scripts are stored in simple text files containing lines with commands that get executed in sequence, one after the other. These files have the special extension BAT or CMD. Files of this type are recognized and executed through an interface (sometimes called a shell) provided by a system file called the command interpreter. On Windows systems, this interpreter is known as cmd.exe.

Running a batch file is a simple matter of just clicking on it. Batch files can also be run in a command prompt or the Start-Run line. In such case, the full path name must be used unless the file's path is in the path environment. Following is a simple example of a Batch Script. This Batch Script when run deletes all files in the current directory.

:: Deletes All files in the Current Directory With Prompts and Warnings
::(Hidden, System, and Read-Only Files are Not Affected)
:: @ECHO OFF
DEL . DR

Batch Script - Environment

This chapter explains the environment related to Batch Script.

Writing and Executing

Typically, to create a batch file, notepad is used. This is the simplest tool for creation of batch files. Next is the execution environment for the batch scripts. On Windows systems, this is done via the command prompt or cmd.exe. All batch files are run in this environment.

Following are the different ways to launch cmd.exe −

Method 1 − Go to C:\Windows\System32 and double click on the cmd file.

Method 2 − Via the run command – The following snapshot shows to find the command prompt(cmd.exe) on Windows server 2012.

Once the cmd.exe is launched, you will be presented with the following screen. This will be your environment for executing your batch scripts.

Environment Variables

In order to run batch files from the command prompt, you either need to go to the location to where the batch file is stored or alternatively you can enter the file location in the path environment variable. Thus assuming that the batch file is stored in the location C:\Application\bin, you would need to follow these instructions for the PATH variable inclusion.

Batch Script - Commands

In this chapter, we will look at some of the frequently used batch commands.

Batch Script - Files

In this chapter, we will learn how to create, save, execute, and modify batch files.

Creating Batch Files

Batch files are normally created in notepad. Hence the simplest way is to open notepad and enter the commands required for the script. For this exercise, open notepad and enter the following statements.

:: Deletes All files in the Current Directory With Prompts and Warnings 
::(Hidden, System, and Read-Only Files are Not Affected) 
:: 
@ECHO OFF 
DEL . 
DR

Saving Batch Files

After your batch file is created, the next step is to save your batch file. Batch files have the extension of either .bat or .cmd. Some general rules to keep in mind when naming batch files −

• Try to avoid spaces when naming batch files, it sometime creates issues when they are called from other scripts.

• Don’t name them after common batch files which are available in the system such as ping.cmd.

The above screenshot shows how to save the batch file. When saving your batch file a few points to keep in mind.

• Remember to put the .bat or .cmd at the end of the file name.
• Choose the “Save as type” option as “All Files”.
• Put the entire file name in quotes “”.

Executing Batch Files

Following are the steps to execute a batch file −

• Step 1 − Open the command prompt (cmd.exe).

• Step 2 − Go to the location where the .bat or .cmd file is stored.

• Step 3 − Write the name of the file as shown in the following image and press the Enter button to execute the batch file.

Modifying Batch Files

Following are the steps for modifying an existing batch file.

• Step 1 − Open windows explorer.

• Step 2 − Go to the location where the .bat or .cmd file is stored.

• Step 3 − Right-click the file and choose the “Edit” option from the context menu. The file will open in Notepad for further editing.

Batch Script - Syntax

Normally, the first line in a batch file often consists of the following command.

ECHO Command

@echo off

By default, a batch file will display its command as it runs. The purpose of this first command is to turn off this display. The command "echo off" turns off the display for the whole script, except for the "echo off" command itself. The "at" sign "@" in front makes the command apply to itself as well.

Documentation

Very often batch files also contains lines that start with the "Rem" command. This is a way to enter comments and documentation. The computer ignores anything on a line following Rem. For batch files with increasing amount of complexity, this is often a good idea to have comments.

First Batch Script Program

Let’s construct our simple first batch script program. Open notepad and enter the following lines of code. Save the file as “List.cmd”.

The code does the following −

• Uses the echo off command to ensure that the commands are not shown when the code is executed.

• The Rem command is used to add a comment to say what exactly this batch file does.

• The dir command is used to take the contents of the location C:\Program Files.

• The ‘>’ command is used to redirect the output to the file C:\lists.txt.

• Finally, the echo command is used to tell the user that the operation is completed.

@echo off 
Rem This is for listing down all the files in the directory Program files 
dir "C:\Program Files" > C:\lists.txt 
echo "The program has completed"

When the above command is executed, the names of the files in C:\Program Files will be sent to the file C:\Lists.txt and in the command prompt the message “The program has completed” will be displayed.

Batch Script - Variables

There are two types of variables in batch files. One is for parameters which can be passed when the batch file is called and the other is done via the set command.

Command Line Arguments

Batch scripts support the concept of command line arguments wherein arguments can be passed to the batch file when invoked. The arguments can be called from the batch files through the variables %1, %2, %3, and so on.

The following example shows a batch file which accepts 3 command line arguments and echo’s them to the command line screen.

@echo off 
echo %1 
echo %2 
echo %3

If the above batch script is stored in a file called test.bat and we were to run the batch as

Test.bat 1 2 3

Following is a screenshot of how this would look in the command prompt when the batch file is executed.

The above command produces the following output.

1 
2 
3

If we were to run the batch as

Example 1 2 3 4

The output would still remain the same as above. However, the fourth parameter would be ignored.

Set Command

The other way in which variables can be initialized is via the ‘set’ command. Following is the syntax of the set command.

Syntax

set /A variable-name=value

where,

• variable-name is the name of the variable you want to set.

• value is the value which needs to be set against the variable.

• /A – This switch is used if the value needs to be numeric in nature.

The following example shows a simple way the set command can be used.

Example

@echo off 
set message=Hello World 
echo %message%

• In the above code snippet, a variable called message is defined and set with the value of "Hello World".

• To display the value of the variable, note that the variable needs to be enclosed in the % sign.

Output

The above command produces the following output.

Hello World

Working with Numeric Values

In batch script, it is also possible to define a variable to hold a numeric value. This can be done by using the /A switch.

The following code shows a simple way in which numeric values can be set with the /A switch.

@echo off 
SET /A a = 5 
SET /A b = 10 
SET /A c = %a% + %b% 
echo %c%

• We are first setting the value of 2 variables, a and b to 5 and 10 respectively.

• We are adding those values and storing in the variable c.

• Finally, we are displaying the value of the variable c.

The output of the above program would be 15.

All of the arithmetic operators work in batch files. The following example shows arithmetic operators can be used in batch files.

@echo off 
SET /A a = 5 
SET /A b = 10 
SET /A c = %a% + %b% 
echo %c% 
SET /A c = %a% - %b% 
echo %c% 
SET /A c = %b% / %a% 
echo %c% 
SET /A c = %b% * %a% 
echo %c%

The above command produces the following output.

15 
-5 
2 
50

Local vs Global Variables

In any programming language, there is an option to mark variables as having some sort of scope, i.e. the section of code on which they can be accessed. Normally, variable having a global scope can be accessed anywhere from a program whereas local scoped variables have a defined boundary in which they can be accessed.

DOS scripting also has a definition for locally and globally scoped variables. By default, variables are global to your entire command prompt session. Call the SETLOCAL command to make variables local to the scope of your script. After calling SETLOCAL, any variable assignments revert upon calling ENDLOCAL, calling EXIT, or when execution reaches the end of file (EOF) in your script. The following example shows the difference when local and global variables are set in the script.

Example

@echo off 
set globalvar = 5
SETLOCAL
set var = 13145
set /A var = %var% + 5
echo %var%
echo %globalvar%
ENDLOCAL

Few key things to note about the above program.

• The ‘globalvar’ is defined with a global scope and is available throughout the entire script.

• The ‘var‘ variable is defined in a local scope because it is enclosed between a ‘SETLOCAL’ and ‘ENDLOCAL’ block. Hence, this variable will be destroyed as soon the ‘ENDLOCAL’ statement is executed.

Output

The above command produces the following output.

13150
5

You will notice that the command echo %var% will not yield anything because after the ENDLOCAL statement, the ‘var’ variable will no longer exist.

Working with Environment Variables

If you have variables that would be used across batch files, then it is always preferable to use environment variables. Once the environment variable is defined, it can be accessed via the % sign. The following example shows how to see the JAVA_HOME defined on a system. The JAVA_HOME variable is a key component that is normally used by a wide variety of applications.

@echo off 
echo %JAVA_HOME%

The output would show the JAVA_HOME directory which would depend from system to system. Following is an example of an output.

C:\Atlassian\Bitbucket\4.0.1\jre

Batch Script - Comments

It’s always a good practice to add comments or documentation for the scripts which are created. This is required for maintenance of the scripts to understand what the script actually does.

For example, consider the following piece of code which has no form of comments. If any average person who has not developed the following script tries to understand the script, it would take a lot of time for that person to understand what the script actually does.

ECHO OFF 
IF NOT "%OS%"=="Windows_NT" GOTO Syntax 
ECHO.%* | FIND "?" >NUL 
IF NOT ERRORLEVEL 1 GOTO Syntax 
IF NOT [%2]==[] GOTO Syntax 
SETLOCAL 
SET WSS= 
IF NOT [%1]==[] FOR /F "tokens = 1 delims = \ " %%A IN ('ECHO.%~1') DO SET WSS = %%A 
FOR /F "tokens = 1 delims = \ " %%a IN ('NET VIEW ^| FIND /I "\\%WSS%"') DO FOR /F 
"tokens = 1 delims = " %%A IN ('NBTSTAT -a %%a ^| FIND /I /V "%%a" ^| FIND "<03>"') 
DO ECHO.%%a %%A 
ENDLOCAL 
GOTO:EOF 
ECHO Display logged on users and their workstations. 
ECHO Usage: ACTUSR [ filter ] 
IF "%OS%"=="Windows_NT" ECHO Where: filter is the first part 
of the computer name^(s^) to be displayed

Comments Using the Rem Statement

There are two ways to create comments in Batch Script; one is via the Rem command. Any text which follows the Rem statement will be treated as comments and will not be executed. Following is the general syntax of this statement.

Syntax

Rem Remarks

where ‘Remarks’ is the comments which needs to be added.

The following example shows a simple way the Rem command can be used.

Example

@echo off 
Rem This program just displays Hello World 
set message=Hello World 
echo %message%

Output

The above command produces the following output. You will notice that the line with the Rem statement will not be executed.

Hello World

Comments Using the :: Statement

The other way to create comments in Batch Script is via the :: command. Any text which follows the :: statement will be treated as comments and will not be executed. Following is the general syntax of this statement.

Syntax

:: Remarks

where ‘Remarks’ is the comment which needs to be added.

The following example shows a simple way the Rem command can be used.

Example

@echo off 
:: This program just displays Hello World 
set message = Hello World 
echo %message%

Output

The above command produces the following output. You will notice that the line with the :: statement will not be executed.

Hello World

Note − If you have too many lines of Rem, it could slow down the code, because in the end each line of code in the batch file still needs to be executed.

Let’s look at the example of the large script we saw at the beginning of this topic and see how it looks when documentation is added to it.

::===============================================================
:: The below example is used to find computer and logged on users
::
::===============================================================
ECHO OFF 
:: Windows version check 
IF NOT "%OS%"=="Windows_NT" GOTO Syntax 
ECHO.%* | FIND "?" >NUL 
:: Command line parameter check 
IF NOT ERRORLEVEL 1 GOTO Syntax
IF NOT [%2]==[] GOTO Syntax 
:: Keep variable local 
SETLOCAL 
:: Initialize variable 
SET WSS= 
:: Parse command line parameter 
IF NOT [%1]==[] FOR /F "tokens = 1 delims = \ " %%A IN ('ECHO.%~1') DO SET WSS = %%A 
:: Use NET VIEW and NBTSTAT to find computers and logged on users 
FOR /F "tokens = 1 delims = \ " %%a IN ('NET VIEW ^| FIND /I "\\%WSS%"') DO FOR /F 
"tokens = 1 delims = " %%A IN ('NBTSTAT -a %%a ^| FIND /I /V "%%a" ^| FIND 
"<03>"') DO ECHO.%%a %%A 
:: Done 
ENDLOCAL
GOTO:EOF 
:Syntax 
ECHO Display logged on users and their workstations. 
ECHO Usage: ACTUSR [ filter ] 
IF "%OS%"=="Windows_NT" ECHO Where: filter is the first part of the 
computer name^(s^) to be displayed

You can now see that the code has become more understandable to users who have not developed the code and hence is more maintainable.

Batch Script - Strings

In DOS, a string is an ordered collection of characters, such as "Hello, World!".

Batch Script - Arrays

Arrays are not specifically defined as a type in Batch Script but can be implemented. The following things need to be noted when arrays are implemented in Batch Script.

• Each element of the array needs to be defined with the set command.
• The ‘for’ loop would be required to iterate through the values of the array.

Creating an Array

An array is created by using the following set command.

set a[0]=1

Where 0 is the index of the array and 1 is the value assigned to the first element of the array.

Another way to implement arrays is to define a list of values and iterate through the list of values. The following example show how this can be implemented.

Example

@echo off 
set list = 1 2 3 4 
(for %%a in (%list%) do ( 
   echo %%a 
))

Output

The above command produces the following output.

1
2
3
4

Accessing Arrays

You can retrieve a value from the array by using subscript syntax, passing the index of the value you want to retrieve within square brackets immediately after the name of the array.

Example

@echo off 
set a[0]=1 
echo %a[0]%

In this example, the index starts from 0 which means the first element can be accessed using index as 0, the second element can be accessed using index as 1 and so on. Let's check the following example to create, initialize and access arrays −

@echo off
set a[0] = 1 
set a[1] = 2 
set a[2] = 3 
echo The first element of the array is %a[0]% 
echo The second element of the array is %a[1]% 
echo The third element of the array is %a[2]%

The above command produces the following output.

The first element of the array is 1 
The second element of the array is 2 
The third element of the array is 3

Modifying an Array

To add an element to the end of the array, you can use the set element along with the last index of the array element.

Example

@echo off 
set a[0] = 1  
set a[1] = 2  
set a[2] = 3 
Rem Adding an element at the end of an array 
Set a[3] = 4 
echo The last element of the array is %a[3]%

The above command produces the following output.

The last element of the array is 4

You can modify an existing element of an Array by assigning a new value at a given index as shown in the following example −

@echo off 
set a[0] = 1 
set a[1] = 2  
set a[2] = 3 
Rem Setting the new value for the second element of the array 
Set a[1] = 5 
echo The new value of the second element of the array is %a[1]%

The above command produces the following output.

The new value of the second element of the array is 5

Iterating Over an Array

Iterating over an array is achieved by using the ‘for’ loop and going through each element of the array. The following example shows a simple way that an array can be implemented.

@echo off 
setlocal enabledelayedexpansion 
set topic[0] = comments 
set topic[1] = variables 
set topic[2] = Arrays 
set topic[3] = Decision making 
set topic[4] = Time and date 
set topic[5] = Operators 

for /l %%n in (0,1,5) do ( 
   echo !topic[%%n]! 
)

Following things need to be noted about the above program −

• Each element of the array needs to be specifically defined using the set command.

• The ‘for’ loop with the /L parameter for moving through ranges is used to iterate through the array.

Output

The above command produces the following output.

Comments 
variables 
Arrays 
Decision making 
Time and date 
Operators

Length of an Array

The length of an array is done by iterating over the list of values in the array since there is no direct function to determine the number of elements in an array.

@echo off 
set Arr[0] = 1 
set Arr[1] = 2 
set Arr[2] = 3 
set Arr[3] = 4 
set "x = 0" 
:SymLoop 

if defined Arr[%x%] ( 
   call echo %%Arr[%x%]%% 
   set /a "x+=1"
   GOTO :SymLoop 
)
echo "The length of the array is" %x%

Output

Output The above command produces the following output.

The length of the array is 4

Creating Structures in Arrays

Structures can also be implemented in batch files using a little bit of an extra coding for implementation. The following example shows how this can be achieved.

Example

@echo off 
set len = 3 
set obj[0].Name = Joe 
set obj[0].ID = 1 
set obj[1].Name = Mark 
set obj[1].ID = 2 
set obj[2].Name = Mohan 
set obj[2].ID = 3 
set i = 0 
:loop 

if %i% equ %len% goto :eof 
set cur.Name= 
set cur.ID=

for /f "usebackq delims==.tokens=1-3" %%j in (`set obj[%i%]`) do ( 
   set cur.%%k=%%l 
) 
echo Name = %cur.Name% 
echo Value = %cur.ID% 
set /a i = %i%+1 
goto loop

The following key things need to be noted about the above code.

• Each variable defined using the set command has 2 values associated with each index of the array.

• The variable i is set to 0 so that we can loop through the structure will the length of the array which is 3.

• We always check for the condition on whether the value of i is equal to the value of len and if not, we loop through the code.

• We are able to access each element of the structure using the obj[%i%] notation.

Output

The above command produces the following output.

Name = Joe 
Value = 1 
Name = Mark 
Value = 2 
Name = Mohan 
Value = 3

Batch Script - Decision Making

Decision-making structures require that the programmer specify one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

Batch Script - Operators

An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulations.

In batch script, the following types of operators are possible.

• Arithmetic operators
• Relational operators
• Logical operators
• Assignment operators
• Bitwise operators

Arithmetic Operators

Batch script language supports the normal Arithmetic operators as any language. Following are the Arithmetic operators available.

Show Example

Relational Operators

Relational operators allow of the comparison of objects. Below are the relational operators available.

Show Example

Logical Operators

Logical operators are used to evaluate Boolean expressions. Following are the logical operators available.

The batch language is equipped with a full set of Boolean logic operators like AND, OR, XOR, but only for binary numbers. Neither are there any values for TRUE or FALSE. The only logical operator available for conditions is the NOT operator.

Show Example

Assignment Operators

Batch Script language also provides assignment operators. Following are the assignment operators available.

Show Example

Bitwise Operators

Bitwise operators are also possible in batch script. Following are the operators available.

Show Example

Following is the truth table showcasing these operators.

Batch Script - DATE and TIME

The date and time in DOS Scripting have the following two basic commands for retrieving the date and time of the system.

DATE

This command gets the system date.

Syntax

DATE

Example

@echo off 
echo %DATE%

Output

The current date will be displayed in the command prompt. For example,

Mon 12/28/2015

TIME

This command sets or displays the time.

Syntax

TIME

Example

@echo off 
echo %TIME%

Output

The current system time will be displayed. For example,

22:06:52.87

Following are some implementations which can be used to get the date and time in different formats.

Date in Format Year-Month-Day

Example

@echo off 
echo/Today is: %year%-%month%-%day% 
goto :EOF 
setlocal ENABLEEXTENSIONS 
set t = 2&if "%date%z" LSS "A" set t = 1 

for /f "skip=1 tokens = 2-4 delims = (-)" %%a in ('echo/^|date') do ( 
   for /f "tokens = %t%-4 delims=.-/ " %%d in ('date/t') do ( 
      set %%a=%%d&set %%b=%%e&set %%c=%%f)) 
endlocal&set %1=%yy%&set %2=%mm%&set %3=%dd%&goto :EOF

Output

The above command produces the following output.

Today is: 2015-12-30

Batch Script - Input / Output

There are three universal “files” for keyboard input, printing text on the screen and printing errors on the screen. The “Standard In” file, known as stdin, contains the input to the program/script. The “Standard Out” file, known as stdout, is used to write output for display on the screen. Finally, the “Standard Err” file, known as stderr, contains any error messages for display on the screen.

Each of these three standard files, otherwise known as the standard streams, are referenced using the numbers 0, 1, and 2. Stdin is file 0, stdout is file 1, and stderr is file 2.

Redirecting Output (Stdout and Stderr)

One common practice in batch files is sending the output of a program to a log file. The > operator sends, or redirects, stdout or stderr to another file. The following example shows how this can be done.

Dir C:\ > list.txt

In the above example, the stdout of the command Dir C:\ is redirected to the file list.txt.

If you append the number 2 to the redirection filter, then it would redirect the stderr to the file lists.txt.

Dir C:\ 2> list.txt

One can even combine the stdout and stderr streams using the file number and the ‘&’ prefix. Following is an example.

DIR C:\ > lists.txt 2>&1

Suppressing Program Output

The pseudo file NUL is used to discard any output from a program. The following example shows that the output of the command DIR is discarded by sending the output to NUL.

Dir C:\ > NUL

Stdin

To work with the Stdin, you have to use a workaround to achieve this. This can be done by redirecting the command prompt’s own stdin, called CON.

The following example shows how you can redirect the output to a file called lists.txt. After you execute the below command, the command prompt will take all the input entered by user till it gets an EOF character. Later, it sends all the input to the file lists.txt.

TYPE CON > lists.txt

Batch Script - Return Code

By default when a command line execution is completed it should either return zero when execution succeeds or non-zero when execution fails. When a batch script returns a non-zero value after the execution fails, the non-zero value will indicate what is the error number. We will then use the error number to determine what the error is about and resolve it accordingly.

Following are the common exit code and their description.

Error Level

The environmental variable %ERRORLEVEL% contains the return code of the last executed program or script.

By default, the way to check for the ERRORLEVEL is via the following code.

Syntax

IF %ERRORLEVEL% NEQ 0 ( 
   DO_Something 
)

It is common to use the command EXIT /B %ERRORLEVEL% at the end of the batch file to return the error codes from the batch file.

EXIT /B at the end of the batch file will stop execution of a batch file.

Use EXIT /B < exitcodes > at the end of the batch file to return custom return codes.

Environment variable %ERRORLEVEL% contains the latest errorlevel in the batch file, which is the latest error codes from the last command executed. In the batch file, it is always a good practice to use environment variables instead of constant values, since the same variable get expanded to different values on different computers.

Let’s look at a quick example on how to check for error codes from a batch file.

Example

Let’s assume we have a batch file called Find.cmd which has the following code. In the code, we have clearly mentioned that we if don’t find the file called lists.txt then we should set the errorlevel to 7. Similarly, if we see that the variable userprofile is not defined then we should set the errorlevel code to 9.

if not exist c:\lists.txt exit 7 
if not defined userprofile exit 9 
exit 0

Let’s assume we have another file called App.cmd that calls Find.cmd first. Now, if the Find.cmd returns an error wherein it sets the errorlevel to greater than 0 then it would exit the program. In the following batch file, after calling the Find.cnd find, it actually checks to see if the errorlevel is greater than 0.

Call Find.cmd

if errorlevel gtr 0 exit 
echo “Successful completion”

Output

In the above program, we can have the following scenarios as the output −

• If the file c:\lists.txt does not exist, then nothing will be displayed in the console output.

• If the variable userprofile does not exist, then nothing will be displayed in the console output.

• If both of the above condition passes then the string “Successful completion” will be displayed in the command prompt.

Loops

In the decision making chapter, we have seen statements which have been executed one after the other in a sequential manner. Additionally, implementations can also be done in Batch Script to alter the flow of control in a program’s logic. They are then classified into flow of control statements.

Looping through Command Line Arguments

The ‘for’ statement can also be used for checking command line arguments. The following example shows how the ‘for’ statement can be used to loop through the command line arguments.

Example

@ECHO OFF 
:Loop 

IF "%1"=="" GOTO completed 
FOR %%F IN (%1) DO echo %%F 
SHIFT 
GOTO Loop 
:completed

Output

Let’s assume that our above code is stored in a file called Test.bat. The above command will produce the following output if the batch file passes the command line arguments of 1,2 and 3 as Test.bat 1 2 3.

1 
2 
3

Batch Script - Functions

A function is a set of statements organized together to perform a specific task. In batch scripts, a similar approach is adopted to group logical statements together to form a function.

As like any other languages, functions in Batch Script follows the same procedure −

• Function Declaration − It tells the compiler about a function's name, return type, and parameters.

• Function Definition − It provides the actual body of the function.

Function Definition

In Batch Script, a function is defined by using the label statement. When a function is newly defined, it may take one or several values as input 'parameters' to the function, process the functions in the main body, and pass back the values to the functions as output 'return types'.

Every function has a function name, which describes the task that the function performs. To use a function, you "call" that function with its name and pass its input values (known as arguments) that matches the types of the function's parameters.

Following is the syntax of a simple function.

:function_name 
Do_something 
EXIT /B 0

• The function_name is the name given to the function which should have some meaning to match what the function actually does.

• The EXIT statement is used to ensure that the function exits properly.

Following is an example of a simple function.

Example

:Display 
SET /A index=2 
echo The value of index is %index% 
EXIT /B 0

Batch Script - Process

In this chapter, we will discuss the various processes involved in Batch Script.

Viewing the List of Running Processes

In Batch Script, the TASKLIST command can be used to get the list of currently running processes within a system.

Syntax

TASKLIST [/S system [/U username [/P [password]]]] [/M [module] | /SVC | /V] [/FI filter]
[/FO format] [/NH]

Following are the description of the options which can be presented to the TASKLIST command.

S.No.	Options & Description
1.	/S system Specifies the remote system to connect to
2.	/U [domain\]user Specifies the user context under which the command should execute.
3.	/P [password] Specifies the password for the given user context. Prompts for input if omitted.
4.	/M [module] Lists all tasks currently using the given exe/dll name. If the module name is not specified all loaded modules are displayed.
5.	/SVC Displays services hosted in each process.
6.	/V Displays verbose task information.
7.	/FI filter Displays a set of tasks that match a given criteria specified by the filter.
8.	/FO format Specifies the output format. Valid values: "TABLE", "LIST", "CSV".
9.	/NH Specifies that the "Column Header" should not show in the output. Valid only for "TABLE" and "CSV" formats.

Examples

TASKLIST

The above command will get the list of all the processes running on your local system. Following is a snapshot of the output which is rendered when the above command is run as it is. As you can see from the following output, not only do you get the various processes running on your system, you also get the memory usage of each process.

Image Name                    PID       Session Name       Session#     Mem Usage
========================= ========    ================ =========== ============
System Idle Process             0        Services            0              4 K
System                          4        Services            0            272 K
smss.exe                      344        Services            0          1,040 K
csrss.exe                     528        Services            0          3,892 K
csrss.exe                     612        Console             1         41,788 K
wininit.exe                   620        Services            0          3,528 K
winlogon.exe                  648        Console             1          5,884 K
services.exe                  712        Services            0          6,224 K
lsass.exe                     720        Services            0          9,712 K
svchost.exe                   788        Services            0         10,048 K
svchost.exe                   832        Services            0          7,696 K
dwm.exe                       916        Console             1        117,440 K
nvvsvc.exe                    932        Services            0          6,692 K
nvxdsync.exe                  968        Console             1         16,328 K
nvvsvc.exe                    976        Console             1         12,756 K
svchost.exe                  1012        Services            0         21,648 K
svchost.exe                   236        Services            0         33,864 K
svchost.exe                   480        Services            0         11,152 K
svchost.exe                  1028        Services            0         11,104 K
svchost.exe                  1048        Services            0         16,108 K
wlanext.exe                  1220        Services            0         12,560 K
conhost.exe                  1228        Services            0          2,588 K
svchost.exe                  1276        Services            0         13,888 K
svchost.exe                  1420        Services            0         13,488 K
spoolsv.exe                  1556        Services            0          9,340 K

tasklist > process.txt

The above command takes the output displayed by tasklist and saves it to the process.txt file.

tasklist /fi "memusage gt 40000"

The above command will only fetch those processes whose memory is greater than 40MB. Following is a sample output that can be rendered.

Image Name                    PID      Session Name     Session#     Mem Usage
=========================   ======== ================ =========== ============
dwm.exe                        916     Console             1        127,912 K
explorer.exe                  2904     Console             1        125,868 K
ServerManager.exe             1836     Console             1         59,796 K
WINWORD.EXE                   2456     Console             1        144,504 K
chrome.exe                    4892     Console             1        123,232 K
chrome.exe                    4976     Console             1         69,412 K
chrome.exe                    1724     Console             1         76,416 K
chrome.exe                    3992     Console             1         56,156 K
chrome.exe                    1168     Console             1        233,628 K
chrome.exe                     816     Console             1         66,808 K

Killing a Particular Process

Allows a user running Microsoft Windows XP professional, Windows 2003, or later to kill a task from a Windows command line by process id (PID) or image name. The command used for this purpose is the TASKILL command.

Syntax

TASKKILL [/S system [/U username [/P [password]]]] { [/FI filter] 
[/PID processid | /IM imagename] } [/T] [/F]

Following are the description of the options which can be presented to the TASKKILL command.

S.No.	Options & Description
1.	/S system Specifies the remote system to connect to
2.	/U [domain\]user Specifies the user context under which the command should execute.
3.	/P [password] Specifies the password for the given user context. Prompts for input if omitted.
4.	/FI FilterName Applies a filter to select a set of tasks. Allows "*" to be used. ex. imagename eq acme* See below filters for additional information and examples.
5.	/PID processID Specifies the PID of the process to be terminated. Use TaskList to get the PID.
6.	/IM ImageName Specifies the image name of the process to be terminated. Wildcard '*' can be used to specify all tasks or image names.
7.	/T Terminates the specified process and any child processes which were started by it.
8.	/F Specifies to forcefully terminate the process(es).

Examples

taskkill /f /im notepad.exe

The above command kills the open notepad task, if open.

taskill /pid 9214

The above command kills a process which has a process of 9214.

Starting a New Process

DOS scripting also has the availability to start a new process altogether. This is achieved by using the START command.

Syntax

START "title" [/D path] [options] "command" [parameters]

Wherein

• title − Text for the CMD window title bar (required.)

• path − Starting directory.

• command − The command, batch file or executable program to run.

• parameters − The parameters passed to the command.

Following are the description of the options which can be presented to the START command.

S.No.	Options & Description
1.	/MIN Start window Minimized
2.	/MAX Start window maximized.
3.	/LOW Use IDLE priority class.
4.	/NORMAL Use NORMAL priority class.
5.	/ABOVENORMAL Use ABOVENORMAL priority class.
6.	/BELOWNORMAL Use BELOWNORMAL priority class.
7.	/HIGH Use HIGH priority class.
8.	/REALTIME Use REALTIME priority class.

Examples

START "Test Batch Script" /Min test.bat

The above command will run the batch script test.bat in a new window. The windows will start in the minimized mode and also have the title of “Test Batch Script”.

START "" "C:\Program Files\Microsoft Office\Winword.exe" "D:\test\TESTA.txt"

The above command will actually run Microsoft word in another process and then open the file TESTA.txt in MS Word.

Batch Script - Aliases

Aliases means creating shortcuts or keywords for existing commands. Suppose if we wanted to execute the below command which is nothing but the directory listing command with the /w option to not show all of the necessary details in a directory listing.

Dir /w

Suppose if we were to create a shortcut to this command as follows.

dw = dir /w

When we want to execute the dir /w command, we can simply type in the word dw. The word ‘dw’ has now become an alias to the command Dir /w.

Creating an Alias

Alias are managed by using the doskey command.

Syntax

DOSKEY [options] [macroname=[text]]

Wherein

• macroname − A short name for the macro.

• text − The commands you want to recall.

Following are the description of the options which can be presented to the DOSKEY command.

Example

Create a new file called keys.bat and enter the following commands in the file. The below commands creates two aliases, one if for the cd command, which automatically goes to the directory called test. And the other is for the dir command.

@echo off
doskey cd = cd/test
doskey d = dir

Once you execute the command, you will able to run these aliases in the command prompt.

Output

The following screenshot shows that after the above created batch file is executed, you can freely enter the ‘d’ command and it will give you the directory listing which means that your alias has been created.

Deleting an Alias

An alias or macro can be deleted by setting the value of the macro to NULL.

Example

@echo off
doskey cd = cd/test
doskey d = dir
d= 

In the above example, we are first setting the macro d to d = dir. After which we are setting it to NULL. Because we have set the value of d to NULL, the macro d will deleted.

Replacing an Alias

An alias or macro can be replaced by setting the value of the macro to the new desired value.

Example

@echo off
doskey cd = cd/test
doskey d = dir

d = dir /w

In the above example, we are first setting the macro d to d = dir. After which we are setting it to dir /w. Since we have set the value of d to a new value, the alias ‘d’ will now take on the new value.

Batch Script - Devices

Windows now has an improved library which can be used in Batch Script for working with devices attached to the system. This is known as the device console – DevCon.exe.

Windows driver developers and testers can use DevCon to verify that a driver is installed and configured correctly, including the proper INF files, driver stack, driver files, and driver package. You can also use the DevCon commands (enable, disable, install, start, stop, and continue) in scripts to test the driver. DevCon is a command-line tool that performs device management functions on local computers and remote computers.

Display driver and device info DevCon can display the following properties of drivers and devices on local computers, and remote computers (running Windows XP and earlier) −

• Hardware IDs, compatible IDs, and device instance IDs. These identifiers are described in detail in device identification strings.

• Device setup classes.

• The devices in a device setup class.

• INF files and device driver files.

• Details of driver packages.

• Hardware resources.

• Device status.

• Expected driver stack.

• Third-party driver packages in the driver store.

• Search for devices DevCon can search for installed and uninstalled devices on a local or remote computer by hardware ID, device instance ID, or device setup class.

• Change device settings DevCon can change the status or configuration of Plug and Play (PnP) devices on the local computer in the following ways −

  • Enable a device.

  • Disable a device.

  • Update drivers (interactive and non-interactive).

  • Install a device (create a devnode and install software).

  • Remove a device from the device tree and delete its device stack.

  • Rescan for Plug and Play devices.

  • Add, delete, and reorder the hardware IDs of root-enumerated devices.

  • Change the upper and lower filter drivers for a device setup class.

  • Add and delete third-party driver packages from the driver store.

DevCon (DevCon.exe) is included when you install the WDK, Visual Studio, and the Windows SDK for desktop apps. DevCon.exe kit is available in the following locations when installed.

%WindowsSdkDir%\tools\x64\devcon.exe
%WindowsSdkDir%\tools\x86\devcon.exe
%WindowsSdkDir%\tools\arm\devcon.exe

Syntax

devcon [/m:\\computer] [/r] command [arguments]

wherein

• /m:\\computer − Runs the command on the specified remote computer. The backslashes are required.

• /r − Conditional reboot. Reboots the system after completing an operation only if a reboot is required to make a change effective.

• command − Specifies a DevCon command.

• To list and display information about devices on the computer, use the following commands −

  • DevCon HwIDs

  • DevCon Classes

  • DevCon ListClass

  • DevCon DriverFiles

  • DevCon DriverNodes

  • DevCon Resources

  • DevCon Stack

  • DevCon Status

  • DevCon Dp_enum

• To search for information about devices on the computer, use the following commands −

  • DevCon Find

  • DevCon FindAll

• To manipulate the device or change its configuration, use the following commands −

  • DevCon Enable

  • DevCon Disable

  • DevCon Update

  • DevCon UpdateNI

  • DevCon Install

  • DevCon Remove

  • DevCon Rescan

  • DevCon Restart

  • DevCon Reboot

  • DevCon SetHwID

  • DevCon ClassFilter

  • DevCon Dp_add

  • DevCon Dp_delete

Examples

Following are some examples on how the DevCon command is used.

List all driver files

The following command uses the DevCon DriverFiles operation to list the file names of drivers that devices on the system use. The command uses the wildcard character (*) to indicate all devices on the system. Because the output is extensive, the command uses the redirection character (>) to redirect the output to a reference file, driverfiles.txt.

devcon driverfiles * > driverfiles.txt

The following command uses the DevCon status operation to find the status of all devices on the local computer. It then saves the status in the status.txt file for logging or later review. The command uses the wildcard character (*) to represent all devices and the redirection character (>) to redirect the output to the status.txt file.

devcon status * > status.txt

The following command enables all printer devices on the computer by specifying the Printer setup class in a DevCon Enable command. The command includes the /r parameter, which reboots the system if it is necessary to make the enabling effective.

devcon /r enable = Printer

The following command uses the DevCon Install operation to install a keyboard device on the local computer. The command includes the full path to the INF file for the device (keyboard.inf) and a hardware ID (*PNP030b).

devcon /r install c:\windows\inf\keyboard.inf *PNP030b

The following command will scan the computer for new devices.

devcon scan

The following command will rescan the computer for new devices.

devcon rescan

Batch Script - Registry

The Registry is one of the key elements on a windows system. It contains a lot of information on various aspects of the operating system. Almost all applications installed on a windows system interact with the registry in some form or the other.

The Registry contains two basic elements: keys and values. Registry keys are container objects similar to folders. Registry values are non-container objects similar to files. Keys may contain values or further keys. Keys are referenced with a syntax similar to Windows' path names, using backslashes to indicate levels of hierarchy.

This chapter looks at various functions such as querying values, adding, deleting and editing values from the registry.

Batch Script - Network

Batch script has the facility to work with network settings. The NET command is used to update, fix, or view the network or network settings. This chapter looks at the different options available for the net command.

Batch Script - Printing

Printing can also be controlled from within Batch Script via the NET PRINT command.

Syntax

PRINT [/D:device] [[drive:][path]filename[...]]

Where /D:device - Specifies a print device.

Example

print c:\example.txt /c /d:lpt1

The above command will print the example.txt file to the parallel port lpt1.

Command Line Printer Control

As of Windows 2000, many, but not all, printer settings can be configured from Windows's command line using PRINTUI.DLL and RUNDLL32.EXE

Syntax

RUNDLL32.EXE PRINTUI.DLL,PrintUIEntry [ options ] [ @commandfile ]

Where some of the options available are the following −

• /dl − Delete local printer.

• /dn − Delete network printer connection.

• /dd − Delete printer driver.

• /e − Display printing preferences.

• /f[file] − Either inf file or output file.

• /F[file] − Location of an INF file that the INF file specified with /f may depend on.

• /ia − Install printer driver using inf file.

• /id − Install printer driver using add printer driver wizard.

• /if − Install printer using inf file.

• /ii − Install printer using add printer wizard with an inf file.

• /il − Install printer using add printer wizard.

• /in − Add network printer connection.

• /ip − Install printer using network printer installation wizard.

• /k − Print test page to specified printer, cannot be combined with command when installing a printer.

• /l[path] − Printer driver source path.

• /m[model] − Printer driver model name.

• /n[name] − Printer name.

• /o − Display printer queue view.

• /p − Display printer properties.

• /Ss − Store printer settings into a file.

• /Sr − Restore printer settings from a file.

• /y − Set printer as the default.

• /Xg − Get printer settings.

• /Xs − Set printer settings.

Testing if a Printer Exists

There can be cases wherein you might be connected to a network printer instead of a local printer. In such cases, it is always beneficial to check if a printer exists in the first place before printing.

The existence of a printer can be evaluated with the help of the RUNDLL32.EXE PRINTUI.DLL which is used to control most of the printer settings.

Example

SET PrinterName = Test Printer
SET file=%TEMP%\Prt.txt
RUNDLL32.EXE PRINTUI.DLL,PrintUIEntry /Xg /n "%PrinterName%" /f "%file%" /q

IF EXIST "%file%" (
   ECHO %PrinterName% printer exists
) ELSE (
   ECHO %PrinterName% printer does NOT exists
)

The above command will do the following −

• It will first set the printer name and set a file name which will hold the settings of the printer.

• The RUNDLL32.EXE PRINTUI.DLL commands will be used to check if the printer actually exists by sending the configuration settings of the file to the file Prt.txt

Batch Script - Debugging

Debugging a batch script becomes important when you are working on a big complex batch script.

Following are the ways in which you can debug the batch file.

Using echo command

A very simple debug option is to make use of echo command in your batch script wherever possible. It will display the message in the command prompt and help you debug where things have gone wrong.

Here is a simple example that displays even numbers based on the input given. The echo command is used to display the result and also if the input is not given. Similarly, the echo command can be used in place when you think that the error can happen. For example, if the input given is a negative number, less than 2, etc.

Example

@echo off  
if [%1] == [] ( 
   echo input value not provided 
   goto stop 
)  
rem Display numbers 
for /l %%n in (2,2,%1) do ( 
   echo %%n 
)  
:stop 
pause 

Output

C:\>test.bat 
10 
2 
4 
6 
8 
10 
22
Press any key to continue ... 

Using pause command

Another way is to pause the batch execution when there is an error. When the script is paused, the developer can fix the issue and restart the processing.

In the example below, the batch script is paused as the input value is mandatory and not provided.

Example

@echo off  
if [%1] == [] ( 
   echo input value not provided 
   goto stop 
) else ( 
   echo "Valid value"     
)  
:stop 
pause 

Output

C:\>test.bat 
 input value not provided 
Press any key to continue.. 

Logging the error messages to another file

It might get hard to debug the error just looking at a bunch of echo displayed on the command prompt. Another easy way out is to log those messages in another file and view it step by step to understand what went wrong.

Here is an example, consider the following test.bat file:

net statistics /Server 

The command given in the .bat file is wrong. Let us log the message and see what we get.

Execute the following command in your command line:

C:\>test.bat > testlog.txt 2> testerrors.txt

The file testerrors.txt will display the error messages as shown below:

The option /SERVER is unknown.  
The syntax of this command is:  
NET STATISTICS 
[WORKSTATION | SERVER]  
More help is available by typing NET HELPMSG 3506.

Looking at the above file the developer can fix the program and execute again.

Using ErrorLevel to detect errors and log them

Errorlevel returns 0 if the command executes successfully and 1 if it fails.

Consider the following example:

@echo off 
PING google.com  
if errorlevel 1 GOTO stop  
:stop 
   echo Unable to connect to google.com 
pause

During execution, you can see errors as well as logs:

C:\>test.bat > testlog.txt

testlog.txt

Pinging google.com [172.217.26.238] with 32 bytes of data: 
Reply from 172.217.26.238: bytes=32 time=160ms TTL=111 
Reply from 172.217.26.238: bytes=32 time=82ms TTL=111 
Reply from 172.217.26.238: bytes=32 time=121ms TTL=111 
Reply from 172.217.26.238: bytes=32 time=108ms TTL=111  
Ping statistics for 172.217.26.238: 
   Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), 
Approximate round trip times in milli-seconds: 
   Minimum = 82ms, Maximum = 160ms, Average = 117ms
   Connected successfully 
Press any key to continue . . .

In case of failure, you will see the following logs inside testlog.txt.

Ping request could not find host google.com. Please check the name and try again. 
Unable to connect to google.com 
Press any key to continue . . .

Batch Script - Logging

Logging in is possible in Batch Script by using the redirection command.

Syntax

test.bat > testlog.txt 2> testerrors.txt

Example

Create a file called test.bat and enter the following command in the file.

net statistics /Server

The above command has an error because the option to the net statistics command is given in the wrong way.

Output

If the command with the above test.bat file is run as

test.bat > testlog.txt 2> testerrors.txt

And you open the file testerrors.txt, you will see the following error.

The option /SERVER is unknown.

The syntax of this command is −

NET STATISTICS
[WORKSTATION | SERVER]

More help is available by typing NET HELPMSG 3506.

If you open the file called testlog.txt, it will show you a log of what commands were executed.

C:\tp>net statistics /Server