Windows bat if else — Ваш верный помощник с OS Windows

Batch file if else

In this tutorial, you will learn about decision making structures that are the batch file if else statements.

Basically programming logic is all about True (1) or False (0). Like any other programming language, batch file if else statements facilitate us to make a decision between true/false or multiple options by imposing a particular condition.

Batch file if else statement

– Syntax

if (condition) dosomething

:: For if..else if
if (condition) (statement1) else (statement2)

So, as the syntax signifies, first a condition is checked and if true, the corresponding statements are executed in the batch file if statement. As for batch file if else, first a condition of if statement is checked and if true, the statement1 is executed else statement2 is executed.

Batch File If Else Flowchart

Here is a flowchart to highlight the concept of if else statement.

Now that we have known about how batch file if else works, let’s go through some examples.

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Batch File If Else Example: Checking Integer Variables And String Variables

To know in depth and details about batch file variables, go through this article.

SET /A a=2
SET /A b=3
SET name1=Aston
SET name2=Martin

:: Using if statement
IF %a%==2 echo The value of a is 2
IF %name2%==Martin echo Hi this is Martin

:: Using if else statements
IF %a%==%b% (echo Numbers are equal) ELSE (echo Numbers are different)
IF %name1%==%name2% (echo Name is Same) ELSE (echo Name is different)
PAUSE

Now this will generate following output.

Batch File If Else Example To Check If Variable Is Defined Or Not

@echo OFF

::If var is not defined SET var = hello
IF "%var%"=="" (SET var=Hello)

:: This can be done in this way as well
IF NOT DEFINED var (SET var=Hello)

Either way, it will set var to 'Hello' as it is not defined previously.

Batch File If Else Example To Check If A File Or Folder Exists

EXIST command is used to check if a file exists or not. Read this article to know details of EXIST and all the other batch file commands.

@echo OFF

::EXIST command is used to check for existence
IF EXIST D:\abc.txt ECHO abc.txt found
IF EXIST D:\xyz.txt (ECHO xyz.txt found) ELSE (ECHO xyz.txt not found)

PAUSE

Now, let’s assume we have "abc.txt" in D drive and "xyz.txt" doesn’t exist in D: , then it will generate following output.

So, that’s all about batch file if else statements. We hope you didn’t have a hard time learning about it and hopefully, by this time, you will know how to use if else in batch file scripting.

Источник

Like any scripting or programming language, the batch language provides conditional execution, i.e.
if condition then command [ else command ]

In DOS (COMMAND.COM), condition can be:

[NOT] ERRORLEVEL number
[/I] [NOT] string1==string2
[NOT] EXIST filename

In NT (CMD.EXE, Windows NT 4 and later) numerical comparisons were added:

number1 EQU number2 (true if numbers are equal)
number1 NEQ number2 (true if numbers are not equal
number1 GTR number2 (true if number1 is greater than number2)
number1 GEQ number2 (true if number1 is greater than or equal to number2)
number1 LSS number2 (true if number1 is less than number2)
number1 LEQ number2 (true if number1 is less than or equal to number2)

Comparisons are really basic, i.e. IF %a% GTR %b% will work, IF %a% + %b% GTR %c% will not.

In the batch language, the keyword then is not used:

IF condition command

The else keyword was introduced in CMD.EXE, and requires «grouping» with parentheses:

IF condition (
	command
) ELSE (
	command
)

or:

IF condition (command) ELSE (command)

or:

IF condition (command) ELSE command

Note: Whenever it says (command) with parentheses, you may insert multiple commands, as will be explained later on this page.

The latter is quite interesting, as it allows ELSE IF constructions:

IF condition1 (
	command1
) ELSE IF condition2 (
	command2
) ELSE IF condition3 (
	command3
) ELSE IF condition4 (
	command4
) ELSE (
	command_none
)

Much better than:

IF condition1 (
	command1
) ELSE (
	IF condition2 (
		command2
	) ELSE (
		IF condition3 (
			command3
		) ELSE (
			IF condition4 (
				command4
			) ELSE (
				command_none
			)
		)
	)
)

Complex conditions

Both COMMAND.COM and CMD.EXE batch language lack and and or statements to combine conditions into a «complex condition».

The and statement is fairly easy to emulate in COMMAND.COM and CMD.EXE alike:

IF condition1 IF condition2 ECHO Condition1 AND Condition2 were both met

or (CMD.EXE only):

IF condition1 (
	IF condition2 (
		ECHO Condition1 AND Condition2 were both met
	)
)

The or functionality requires more code:

SET AtLeastOneConditionMet=false
IF condition1 SET AtLeastOneConditionMet=true
IF condition2 SET AtLeastOneConditionMet=true
IF "%AtLeastOneConditionMet%"=="true" ECHO Condition1 OR condition2 OR both were met

One-Liners

Most program executables set an ErrorLevel stating success or failure of their execution.
This allows for error handling by using IF ERRORLEVEL 1 ... or IF %ErrorLevel% NEQ 0 ..., e.g.:

DIR somefolder
IF %ErrorLevel% EQU 0 (
	ECHO Directory "somefolder" exists
) ELSE (
	ECHO Directory "somefolder" does not exist
)

CMD.EXE for both OS/2 and Windows NT 4 and later offer a way to create «one-liners», making the error handling code a bit simpler:

One-Liners
Syntax	Description	Equivalent to
`command1 & command2`	Execute command2 after execution of command1 has finished	`command1 command2`
`command1 && command2`	Execute command2 only if execution of command1 has finished successfully	`command1 IF %ErrorLevel% EQU 0 command2`
`command1 \|\| command2`	Execute command2 only if execution of command1 has finished unsuccessfully	`command1 IF %ErrorLevel% NEQ 0 command2`

Note:

Conditional execution based on success or failure of a previous command will only work if that previous command sets an ErrorLevel based on its success or failure.

Some examples:

FORMAT A: /Q && COPY C:\DATA\*.* A:
will copy all files from C:\DATA to diskette IF and ONLY IF the format succeeds.

XCOPY C:\*.* D:\ /S 2>&1> NUL || ECHO Something terrible happened
will display your own custom error message if XCOPY fails.

Complex One-Liners

What if we want a number of commands to be executed, and abort if any of these commands fails?

command1
IF %ErrorLevel% EQU 0 (
	command2
	IF %ErrorLevel% EQU 0 (
		command3
		IF %ErrorLevel% NEQ 0 (
			ECHO Error 3
		)
	) ELSE (
		ECHO Error 2
	)
) ELSE (
	ECHO Error 1
)

If we are not interested in the distinction between errors 1,2 or 3, we can simplify the code:

command1 && command2 && command3 || ECHO Error

For simple commands this will work, but sometimes I got unexpected results in constructions like these.
Darin Schnetzler found a more reliable way to write these one-liners:

(command1) && (command2) && (command3) || (ECHO Error)

If any command in the «chain» fails, the rest will be skipped and the error handling (in this case ECHO Error) will be executed.

The parentheses allow (sub)grouping of commands too:

(command1 & command2) && (command3) && (command4) || (ECHO Error)

In this case, if command1 fails, command2 will still be executed, and if command2 succeeds, command3 will be executed, etc.
Error handling will only be triggered by failure of command2 .. command4

Warning Batch code can soon become unreadable using these one-liner constructions.
You may want to spread the code over multiple lines again:
( command1 command2 ) && ( command3 ) && ( command4 ) || ( ECHO Error )

Thanks Darin

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Введение в принятие решений в скриптах batch

Здравствуйте, ambitные программисты! Сегодня мы окунемся в захватывающий мир принятия решений в скриптах batch. Как ваш доброжелательный сосед-учитель информатики, я здесь, чтобы провести вас через это путешествие с множеством примеров и капелькой юмора. Так что пристегнитесь и lets get started!

Принятие решений — это как выбор flavors мороженого — все дело в том, чтобы делать выбор на основе определенных условий. В скриптах batch мы используем эти решения, чтобы сделать наши скрипты умнее и гибче.

Оператор IF: Ваш первый Decision Maker

Основной оператор IF

Оператор IF — это основа принятия решений в Batch. Это как светофор для вашего кода — он говорит вашему скрипту, когда идти и когда останавливаться.

Давайте начнем с простого примера:

@echo off
IF EXIST "C:\MyFile.txt" echo File exists!

В этом скрипте мы проверяем, существует ли файл с именем «MyFile.txt» на диске C:. Если да, мы выводим «File exists!». Это так просто!

Оператор IF-ELSE: Два пути на выбор

Теперь добавим clause ELSE к нашему оператору IF. Это как Plan B:

@echo off
IF EXIST "C:\MyFile.txt" (
echo File exists!
) ELSE (
echo File does not exist!
)

Здесь, если файл не существует, мы увидим «File does not exist!». Это как спрашивать: «Есть ли пицца в холодильнике? Если да, съешь ее; если нет, закажи!»

Сравнительные операторы: Инструмент для принятия решений

При принятии решений нам часто нужно что-то сравнивать. В Batch у нас есть несколько операторов сравнения, которые помогут нам. Вот удобная таблица этих операторов:

Оператор	Описание
EQU	Равно
NEQ	Не равно
LSS	Меньше
LEQ	Меньше или равно
GTR	Больше
GEQ	Больше или равно

Давайте используем их в примере:

@echo off
SET /A age=25
IF %age% GEQ 18 (
echo You're an adult!
) ELSE (
echo You're still a minor.
)

В этом скрипте мы проверяем, достиг ли возраст 18 лет. Если да, мы объявляем человека взрослым. Это как виртуальныйouncer для вашего кода!

Оператор GOTO: Перемещение по скрипту

Иногда нужно перейти к различным частям вашего скрипта на основе решения. Вот где оператор GOTO comes in handy. Это как телепортация для вашего кода!

@echo off
SET /P choice=Enter 1 for Hello, 2 for Goodbye:
IF %choice%==1 GOTO hello
IF %choice%==2 GOTO goodbye
GOTO end

:hello
echo Hello, World!
GOTO end

:goodbye
echo Goodbye, World!
GOTO end

:end
echo Script finished!

Этот скрипт спрашивает пользователя сделать выбор и затем переходит к соответствующему разделу с помощью GOTO. Это как «Выбери свое собственное приключение» книга, но в виде кода!

Вложенные IF операторы: Решения в решениях

Иногда одного решения недостаточно. Нам нужно принимать решения на основе результатов других решений. Вот где появляются вложенные IF операторы:

@echo off
SET /P age=Enter your age:
IF %age% GEQ 18 (
IF %age% LSS 65 (
echo You're an adult of working age.
) ELSE (
echo You're a senior citizen.
)
) ELSE (
echo You're a minor.
)

Этот скрипт классифицирует человека по возрасту, используя вложенные IF операторы. Это как матрешка принятия решений!

Команда CHOICE: Интерактивное принятие решений

Команда CHOICE позволяет нам создавать интерактивные меню для ввода пользователя. Это как создание теста с выбором ответов в вашем скрипте:

@echo off
ECHO What's your favorite color?
ECHO 1. Red
ECHO 2. Blue
ECHO 3. Green
CHOICE /C 123 /N /M "Enter your choice (1-3):"
IF ERRORLEVEL 3 ECHO You chose Green
IF ERRORLEVEL 2 ECHO You chose Blue
IF ERRORLEVEL 1 ECHO You chose Red

Этот скрипт presenting a menu and reacts based on the user’s choice. Это как быть mentalist, но с кодом!

Заключение

И вот мы arrived, друзья! Мы совершили путешествие по земле принятия решений в скриптах batch. От простых IF операторов до сложных вложенных условий, теперь у вас есть сила сделать свои скрипты умнее и интерактивнее.

помните, что практика makes perfect. Попробуйте создать свои собственные скрипты с использованием этих техник. Может быть, создайте скрипт, который решает, что есть на обед в зависимости от дня недели? Возможности безграничны!

Счастливого скриптинга и пусть ваши решения всегда приведут к безошибочному коду!

Credits: Image by storyset

Источник

Understanding the IF ELSE Structure
Using IF ELSE with Comparison Operators
Nested IF ELSE Statements
Practical Applications of IF ELSE in Batch Scripts
Conclusion
FAQ

When it comes to scripting, especially in the Windows environment, Batch scripts are a powerful tool for automating tasks. One of the essential structures in any programming language is the conditional statement, and in Batch scripting, the IF ELSE condition is crucial for decision-making.

This tutorial will delve into the structure of the IF ELSE condition in a Batch Script. By the end, you’ll have a solid understanding of how to implement these conditions effectively, enabling you to create more dynamic and responsive scripts. Whether you’re a beginner or looking to refine your skills, this guide will provide you with valuable insights and practical examples.

Understanding the IF ELSE Structure

The IF ELSE condition in Batch scripting allows you to execute different commands based on specific conditions. This structure is fundamental for creating scripts that can respond to various inputs or states.

The basic syntax of the IF statement is as follows:

IF condition (
    command1
) ELSE (
    command2
)

In this syntax, if the specified condition is true, command1 is executed; if false, command2 is executed. This simple yet powerful structure can significantly enhance your script’s functionality.

For example, let’s say you want to check if a file exists before executing a command. You can use the following Batch script:

IF EXIST myfile.txt (
    echo File exists.
) ELSE (
    echo File does not exist.
)

Output:

In this case, if myfile.txt is present in the directory, the script will output “File exists.” Otherwise, it will inform you that the file is missing. This is a straightforward application of the IF ELSE condition, showcasing its utility in real-world scenarios.

Using IF ELSE with Comparison Operators

Another powerful feature of the IF ELSE condition is the ability to use comparison operators. These operators allow you to compare numbers, strings, and even file attributes. The common comparison operators in Batch scripts include:

== for equality
NEQ for not equal
LSS for less than
LEQ for less than or equal to
GTR for greater than
GEQ for greater than or equal to

Here’s an example that demonstrates how to use these operators in a Batch script:

SET /A num1=10
SET /A num2=20

IF %num1% LSS %num2% (
    echo num1 is less than num2.
) ELSE (
    echo num1 is not less than num2.
)

Output:

In this example, we set two numeric variables, num1 and num2. The script checks if num1 is less than num2. Since this condition is true, it outputs the corresponding message. Using comparison operators effectively can help you create more complex logic in your Batch scripts.

Nested IF ELSE Statements

Sometimes, you may need to evaluate multiple conditions. In such cases, you can nest IF ELSE statements. This allows for more intricate decision-making processes within your Batch scripts. Here’s how you can implement nested IF ELSE statements:

SET /A score=85

IF %score% GEQ 90 (
    echo Grade: A
) ELSE (
    IF %score% GEQ 80 (
        echo Grade: B
    ) ELSE (
        echo Grade: C
    )
)

Output:

In this script, we first check if the score is greater than or equal to 90. If true, it outputs “Grade: A.” If not, it checks if the score is greater than or equal to 80. Since our score is 85, it outputs “Grade: B.” This structure allows for a clear, organized way to handle multiple conditions, making your scripts easier to read and maintain.

Practical Applications of IF ELSE in Batch Scripts

The applications of IF ELSE statements in Batch scripts are vast. Whether you are automating backups, managing system configurations, or creating user interactions, these conditions can be employed to enhance your scripts’ functionality.

For instance, consider a scenario where you want to check if a user has administrative privileges before allowing them to execute a sensitive command. You can implement this check using the IF ELSE structure:

NET SESSION >nul 2>&1
IF %ERRORLEVEL% NEQ 0 (
    echo You need administrative privileges to run this command.
) ELSE (
    echo Running sensitive command...
)

Output:

You need administrative privileges to run this command.

In this script, we use the NET SESSION command to check for administrative privileges. If the user doesn’t have the required permissions, an appropriate message is displayed. This example illustrates how IF ELSE conditions can be used to enforce security measures in your scripts.

Conclusion

The IF ELSE condition is a fundamental part of Batch scripting that allows you to add decision-making capabilities to your scripts. By understanding its structure and applications, you can create more dynamic and responsive Batch scripts. From simple file existence checks to complex nested conditions, mastering this concept will significantly enhance your scripting skills. As you continue to explore Batch scripting, remember that practice is key. Experiment with different conditions and commands to see how they interact, and soon you’ll find yourself creating robust scripts that automate tasks efficiently.

FAQ

What is the purpose of the IF ELSE condition in Batch scripts?
The IF ELSE condition allows scripts to execute different commands based on specific conditions, enhancing decision-making capabilities.

Can I use comparison operators in Batch scripts?
Yes, Batch scripts support various comparison operators such as ==, NEQ, LSS, LEQ, GTR, and GEQ.
How do I check if a file exists in a Batch script?
You can use the IF EXIST command to check for a file’s presence and execute commands based on that condition.
What are nested IF ELSE statements?
Nested IF ELSE statements allow you to evaluate multiple conditions within a Batch script, providing a more complex decision-making structure.
Can I use IF ELSE conditions for user input validation?
Absolutely! IF ELSE conditions can be used to validate user inputs and ensure they meet specific criteria before proceeding with script execution.

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Источник

Overview
Part 1 – Getting Started
Part 2 – Variables
Part 3 – Return Codes
Part 4 – stdin, stdout, stderr
Part 5 – If/Then Conditionals
Part 6 – Loops
Part 7 – Functions
Part 8 – Parsing Input
Part 9 – Logging
Part 10 – Advanced Tricks

Computers are all about 1’s and 0’s, right? So, we need a way to handle when some condition is 1, or else do something different
when it’s 0.

The good news is DOS has pretty decent support for if/then/else conditions.

Checking that a File or Folder Exists

IF EXIST "temp.txt" ECHO found

Or the converse:

IF NOT EXIST "temp.txt" ECHO not found

Both the true condition and the false condition:

IF EXIST "temp.txt" (
    ECHO found
) ELSE (
    ECHO not found
)

NOTE: It’s a good idea to always quote both operands (sides) of any IF check. This avoids nasty bugs when a variable doesn’t exist, which causes
the the operand to effectively disappear and cause a syntax error.

Checking If A Variable Is Not Set

IF "%var%"=="" (SET var=default value)

IF NOT DEFINED var (SET var=default value)

Checking If a Variable Matches a Text String

SET var=Hello, World!

IF "%var%"=="Hello, World!" (
    ECHO found
)

Or with a case insensitive comparison

IF /I "%var%"=="hello, world!" (
    ECHO found
)

Artimetic Comparisons

SET /A var=1

IF /I "%var%" EQU "1" ECHO equality with 1

IF /I "%var%" NEQ "0" ECHO inequality with 0

IF /I "%var%" GEQ "1" ECHO greater than or equal to 1

IF /I "%var%" LEQ "1" ECHO less than or equal to 1

Checking a Return Code

IF /I "%ERRORLEVEL%" NEQ "0" (
    ECHO execution failed
)

<< Part 4 – stdin, stdout, stderr

Part 6 – Loops >>

Источник