Conditionally perform a command several times.
FOR %%parameter IN (set) DO command
syntax-FOR-Files-Rooted at Path
FOR /R [[drive:]path] %%parameter IN (set) DO command
FOR /D %%parameter IN (folder_set) DO command
syntax-FOR-List of numbers
FOR /L %%parameter IN (start,step,end) DO command
FOR /F ["options"] %%parameter IN (filenameset) DO command
FOR /F ["options"] %%parameter IN ("Text string to process") DO command
FOR /F ["options"] %%parameter IN ('command to process') DO command
The operation of the FOR command can be summarised as...
Take a set of data
Make a FOR Parameter %%G equal to some part of that data
Perform a command (optionally using the parameter as part of the command).
Repeat for each item of data
If you are using the FOR command at the command line rather than in a batch program, specify %parameter instead of %%parameter.
The FOR command supports implicit parameter definitions. The first parameter always has to be defined explicitly and this must be a single character.
e.g. FOR %%G IN ...
In each iteration of a FOR loop, the IN ( ....) clause is evaluated and %%G set to a different value. If this results in a single value then %%G is set = to that value and the command is performed.
If this results in a multiple values then extra parameters are implicitly defined to hold each. These are automatically assigned in alphabetical order %%H %%I %%J ...
FOR /F %%G IN ("This is a long sentence") DO @echo %%G %%H %%J
will result in the output
This is long
You can of course pick any letter of the alphabet other than %%G.
%%G is a good choice because it does not conflict with any of the pathname format letters (a, d, f, n, p, s, t, x) and provides the longest run of non-conflicting letters for use as implicit parameters.
G > H > I > J > K > L > M
Other Environment variables
Environment variables within a FOR loop are expanded at the beginning of the loop and won't change until AFTER the end of the DO section. So in the following snippet %count% will not display the expected result:
FOR /f "tokens=*" %%G IN ('dir /b') DO (
set /a count+=1)
To force the variable to be evaluated during each iteration, use the CALL :subroutine mechanism to take the evaluation outside of the FOR loop.
FOR /f "tokens=*" %%G IN ('dir /b') DO (call :s_do_sums %%G)
set /a count+=1
Nested FOR commands
FOR commands can be nested FOR %%G... DO (for %%U... do ...)
when nesting commands choose a different letter for each part. you can then refer to both parameters in the final DO command.
If Command Extensions are disabled, the FOR command will only support the basic syntax with no enhanced variables:
FOR %%parameter IN (set) DO command [command-parameters]
About the Author
FortyPoundHead has posted a total of 1974 articles.
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