NT Syntax


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 

syntax-FOR-File contents   
      FOR /F ["options"] %%parameter IN (filenameset) DO command 

      FOR /F ["options"] %%parameter IN ("Text string to process") DO command

syntax-FOR-Command Results 
      FOR /F ["options"] %%parameter IN ('command to process') DO command

The operation of the FOR command can be summarised as...

If you are using the FOR command at the command line rather than in a batch program, specify %parameter instead of %%parameter.

FOR Parameters

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 example

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:

SET count=1 
FOR /f "tokens=*" %%G IN ('dir /b') DO (
   echo %count%:%%G
   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.

SET count=1 
FOR /f "tokens=*" %%G IN ('dir /b') DO (call :s_do_sums %%G)
GOTO :eof
  echo %%count%%:%1
  set /a count+=1
GOTO :eof

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]

"In expanding the field of knowledge, we but increase the horizon of ignorance" - Henry Miller

Related Commands:

FOR - Loop through a set of files in one folder
FOR /R - Loop through files (recurse subfolders)
- Loop through several folders
FOR /L - Loop through a range of numbers
FOR /F - Loop through items in a text file
FOR /F - Loop through the output of a command

FORFILES - Batch process multiple files
GOTO - Direct a batch program to jump to a labelled line
IF - Conditionally perform a command

Equivalent Linux BASH commands:

- Divide a file into several columns
for var in [list]; do - Expand list, and execute commands
eval - Evaluate several commands/arguments
until - Execute commands (until error)
while - Execute commands

Simon Sheppard