How-to: Extract part of a variable (substring)

It is possible to retrieve specific characters from a string variable.

Syntax
      %variable:~start_index%
      %variable:~start_index,length%

This can include negative numbers:

      %variable:~start_index, -length%
      %variable:~-start_index,length%
      %variable:~-start_index,-length%

start_index Defines the starting point for the string returned, for positive numbers this is the number of characters skipped.
A negative number will count backwards from the end of the string.

length Defines the number of characters to return as a string. For positive numbers this is the number of characters to return after the start_index, for negative numbers this is a number of characters to return counting back from the end of the string.

This syntax adds a little extra flexibility compared to a standard Mid() function, which is best illustrated by the examples below.

Examples

The variable _test is used for all the following examples:

SET "_test=123456789abcdef0"

::Extract only the first 5 characters

 SET "_result=%_test:~0,5%"
 ECHO %_result%          =12345

::Skip 7 characters and then extract the next 5

 SET "_result=%_test:~7,5%"
 ECHO %_result%          =89abc

::Skip 7 characters and then extract everything else

 SET "_result=%_test:~7%"
 ECHO %_result%          =89abcdef0

::Extract only the last 7 characters

 SET "_result=%_test:~-7%"
 ECHO %_result%          =abcdef0

::Extract everything BUT the last 7 characters

 SET "_result=%_test:~0,-7%"
 ECHO %_result%          =123456789

::Extract between 7 from the front and 5 from the end

 SET "_result=%_test:~7,-5%"
 ECHO %_result%          =89ab

::Go back 7 from the end then extract 5 towards the end

 SET "_result=%_test:~-7,5%"
 ECHO %_result%          =abcde

::Extract between 7 from the end and 5 from the end

   SET "_result=%_test:~-7,-5%"
   ECHO %_result%        =ab

This variable substring syntax only works for CMD environment variables, like %MYVAR%, it will not work with FOR parameter variables, like %%G, however a simple workaround is to set a variable first: Set MYVAR=%%G and then find the substring of the new variable.

If you need to access the current value of a variable within a FOR loop, then you may need to use delayed expansion. By default variable expansion will happen just once at the start of each loop.

The start_index may be omitted, defaulting to zero, though many prefer to include it to help document what the command is doing.

Advanced Usage of :~

You can use the :~ syntax and provide each of the parameters from other variables, for example if you have:

 Set "_donor=88477"
 Set "_startchar=2"

To extract digit # 2 from %_donor% you might try:

 SET "_substring=%_donor:~%_startchar%,1%"

Unfortunately this will not work because the :~ syntax expects a value not a variable. To get around this use the CALL command like this:

@Echo off
SET "_donor=884777"
SET "_startchar=2"
SET "_length=1"
CALL SET "_substring=%%_donor:~%_startchar%,%_length%%%"
ECHO (%_substring%) 

Alternatively, you can use Setlocal EnableDelayedExpansion, and use !_donor! to place the value into the expression:

SET "_substring=!_donor:~%_startchar%,%_length%!"

:: Credits:
:: Clay Calvert - alt.msdos.batch.nt
:: Ritchie Lawrence - alt.msdos.batch.nt

Don’t build your castle in other people’s kingdoms ~ Chris Zukowski (zukalous)

Related commands

How-to: VarSearch - Search & replace part of a variable.
How-to: strlen.cmd - Get string length.
PowerShell equivalent: Substring() - Return part of a longer string.