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Help for a batch script. Replace the substring of the delayed extension queue with another DelayedExpansion Var parameter

Mostly I'm trying to do! var1: SomeText =! var2 !! but this code does not work. What am I missing?

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The extension order is critical when performing a search and replace operation using a variable to search and / or replace. The internal variable must be expanded before the start of the external search and replacement. Trying to use a delayed extension for both obviously cannot work, because the delayed extension occurs at one point in time.

The classic method of expanding a variable inside another variable uses a delayed extension for the external and normal for the internal: echo !var1:SomeText=%var2%!"

I'm going to suggest that you wanted to use a deferred extension for some reason. Perhaps the extension takes place inside a block of code, and one of the variables was set in the same block. A normal extension will not work because it cannot see the value that was assigned in the block until the block completes.

Solution 1

One way to solve the problem is to use CALL:

 call echo %%var1:SomeText=!var2!%%

This works as follows:

  • The percentage phase of the analyzer converts two percent to one percent, resulting in
    call echo %var1:SomeText=!var2!%

  • Extension delay is expanding! var2 !, resulting in
    call echo %var1:SomeText=ReplacementText%

  • CALL ECHO is performed and an additional level of percentage processing is performed. Search and replace are performed, resulting in the display of ResultOfSearchAndReplace .

It works, but it is relatively slow. It may also have problems if the extended value has special characters such as > , & or | . I rarely use this technique.

Decision 2

A quick and reliable method is to do the expansion in two steps. First pass the value !var2! into the FOR variable. Then you can use the FOR variable as a replacement string and use the slow extension for the second step. This completely eliminates the more fragile increase in interest.

 for /f "delims=" %%A in ("!var2!") do echo !var1:SomeText=%%A!

The above works because the variable expansion of the FOR variable occurs before the deferred extension.

This is by far my preferred method for attacking this issue.

For a more detailed explanation of the various phases of the parser analyzer, see jeb's answer to How is the Windows Command Interpreter Script Interpreter (CMD.EXE)?

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