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Batch programmers often confuse single percent signs (%) and double percent signs (%%) when used in batch files. The FOR command uses %f when executed on the command line, but in a batch file, it uses %%f instead of a single percent sign.

The symbols %, %%, , %variable%and !variable!have some basic differences and are used differently on the command line and in batch files.

This article explains the difference between %and in batch files %%. It also discusses the use of %and in batch files and cmd %%, as well as environment variables and loop variables.

Using % and %% in CMD

In a command shell, % variables specify single-letter replaceable parameters. Ms-DOS uses %1,%2,...,%9 as replaceable command line parameters, that is, %1 will be replaced by the first parameter passed to the batch file.

The following example shows that a single percent sign with a variable (%a) acts as a null character:

set a="Hello World"
echo %a

When percent signs are used around a variable, %VARIABLE%, it acts as an environment variable and displays the set value when used with the echo command. %VARIABLE% can be set using the set command and accessed using the echo command.

An example is shown below.

set a="Hello World"
echo %a%

Using % and %% in batch files

In a batch file, the command line shell reads all commands from left to right. If it reads a percent sign, it moves on to the next character.

It will %%read as a single %ie %%replace with a single percent and read the third character. If it is in a FOR loop it will evaluate it like in a FOR loop.

The following example explains the use of %% in a FOR loop.

FOR /L %%3 in (1,1,3) Do Echo %%3
PAUSE

Output:

If not a FOR loop, it is read as an ordinary character and behaves the same as the %variable command when executed directly in a command-line shell.

set a="Hello World"
echo %%a
PAUSE

Output:

If the character after the % sign is a number, it is read as a command line argument. If the character after the % sign is neither a % sign nor a number, it is read as a variable until the next % sign; then, its value is displayed.

For example,

set a="Hello World"
echo %a%
PAUSE

Output:

To use pure % signs (such as 50%) in a batch file, you need to use %% instead of a single % sign.

set a="The battery is charged 50%%"
echo %a%
PAUSE

Output:

%and %%are mainly used in the FOR command. When the FOR command is used outside a batch file, a single %symbol works well.

However, when used in a batch file, it should be replaced with double %% to avoid any errors. Also, it is recommended to avoid using numbers with % sign as FOR command parameters.

Using delayed expansion in batch files

Sometimes, using %VARIABLE% in a batch file does not print the result. This is because when percent expansion is done, the variable is expanded before execution (i.e. at parsing time).

When used in a loop, the variable is expanded only once.

To solve this problem, you can use delayed expansion, which !variable!replaces percent signs ( ) with exclamation points ( %variable%). When delayed expansion is enabled, variables are expanded at execution time.

In a loop, it is expanded at each iteration. Therefore, it is recommended to use % instead of ! to expand variables, mainly when using loops.

To enable delayed expansion, we can use the SETLOCAL EnableDelayedExpansion command and replace % with !, as shown in the following example.

@echo off
setlocal EnableDelayedExpansion
:: count to 5, storing results in a variable
set n=0
FOR /l %%G in (1,1,5) Do (echo [!n!] & set /a n+=1)
echo Total = %n%

Output:

So, we discussed the difference between the %and %%symbols when used in batch files and cmd. We covered almost everything including the use of delayed expansion.