How to substitute variable contents in a Windows batch file

Question

I\'m writing a simple script to substitute text in an environment variable with other text. The trouble I get is with the substituted or substituted text being pulled from o

Answer 1

I try to avoid using SETLOCAL enabledelayedexpansion ... ENDLOCAL all (or nearly all) the time, because usually I want to set or modify a few variables and I want the new values to be available in other areas of the script or after the batch script ends (SETLOCAL|ENDLOCAL will forget about any new variables or changes to variables in the "SETLOCAL" part of the script. Sometimes that's handy, but for me I find it's usually not.

Currently I use the method described by @Zuzel, but before I knew about that method, I used to use this, which is very similar (but looks a bit more complicated):

for /F "usebackq delims=" %%f in (`echo set "a=^%a:%b%=%c%^%"`) do @%%f

example script:

@echo off

set a=The fat cat
set b=fat
set c=thin

@echo.
@echo before: "%a%"

@echo replace "%b%" with "%c%" in "%a%" using for:
for /F "usebackq delims=" %%f in (`echo set "a=%%a:%b%=%c%%%"`) do @%%f
@echo after for:  "%a%"

goto :EOF

the output from running the script:

before: "The fat cat"
replace "fat" with "thin" in "The fat cat" using for:
after for:  "The thin cat"

I like this method because you can call external programs (or internal commands) using modified variables and also capture and process the output of the command (line by line).

But, Zuzel's method is simpler and cleaner for most situations, including the one you described.

Note:

Both of these methods (and also SETLOCAL enabledelayedexpansion ... ENDLOCAL, of course), only work correctly if run from within a batch script. If you try to use either of these two methods ("call" or "for") directly in a command prompt window, you will get something different from what the output was running from a script.

For example, run this as a script:

@echo off

set a=The fat cat
set b=fat
set c=thin
set d=calico
set e=sleepy

@echo.
@echo before: "%a%"
@echo.

@echo replace "%b%" with "%c%" in "%a%" using call:
call set a=%%a:%b%=%c%%%
@echo after call: "%a%" ("%b%" to "%c%")

@echo.
@echo replace "%c%" with "%d%" in "%a%" using for:
for /F "usebackq delims=" %%f in (`echo set "a=%%a:%c%=%d%%%"`) do @%%f
@echo after for:  "%a%" ("%c%" to "%d%")

@echo.
@echo replace "%d%" with "%e%" in "%a%" using call:
call set a=%%a:%d%=%e%%%
@echo after call: "%a%" ("%d%" to "%e%")

the output from running the script:

before: "The fat cat"

replace "fat" with "thin" in "The fat cat" using call:
after call: "The thin cat" ("fat" to "thin")

replace "thin" with "calico" in "The thin cat" using for:
after for:  "The calico cat" ("thin" to "calico")

replace "calico" with "sleepy" in "The calico cat" using call:
after call: "The sleepy cat" ("calico" to "sleepy")

Now, run those commands directly in a command prompt window:

c:\>
c:\>set a=The fat cat

c:\>set b=fat

c:\>set c=thin

c:\>set d=calico

c:\>set e=sleepy

c:\>
c:\>@echo.


c:\>@echo before: "%a%"
before: "The fat cat"

c:\>@echo.


c:\>
c:\>@echo replace "%b%" with "%c%" in "%a%" using call:
replace "fat" with "thin" in "The fat cat" using call:

c:\>call set a=%%a:%b%=%c%%%

c:\>@echo after call: "%a%" ("%b%" to "%c%")
after call: "%The thin cat%" ("fat" to "thin")

c:\>
c:\>@echo.


c:\>@echo replace "%c%" with "%d%" in "%a%" using for:
replace "thin" with "calico" in "%The thin cat%" using for:

c:\>for /F "usebackq delims=" %f in (`echo set "a=%%a:%c%=%d%%%"`) do @%f

c:\>@echo after for:  "%a%" ("%c%" to "%d%")
after for:  "%%The calico cat%%" ("thin" to "calico")

c:\>
c:\>@echo.


c:\>@echo replace "%d%" with "%e%" in "%a%" using call:
replace "calico" with "sleepy" in "%%The calico cat%%" using call:

c:\>call set a=%%a:%d%=%e%%%

c:\>@echo after call: "%a%" ("%d%" to "%e%")
after call: "%%%The sleepy cat%%%" ("calico" to "sleepy")

c:\>

examine the before and after output lines from the command prompt window:

before: "The fat cat"

replace "fat" with "thin" in "The fat cat" using call:
after call: "%The thin cat%" ("fat" to "thin")

replace "thin" with "calico" in "%The thin cat%" using for:
after for:  "%%The calico cat%%" ("thin" to "calico")

replace "calico" with "sleepy" in "%%The calico cat%%" using call:
after call: "%%%The sleepy cat%%%" ("calico" to "sleepy")

Notice that the substitutions are made correctly, but also notice that with running these commands directly in the command prompt window, it adds a set of "%" (percent signs) before and after the expected value each time the substitution is made. So, it makes it difficult to test any of these methods directly in the command prompt window.