Use the following for statement syntax with /f option
FOR /F ["options"] %variable IN (file-set) DO command [command-parameters] FOR /F ["options"] %variable IN ("string") DO command [command-parameters] FOR /F ["options"] %variable IN ('command') DO command [command-parameters] or, if usebackq option present: FOR /F ["options"] %variable IN (file-set) DO command [command-parameters] FOR /F ["options"] %variable IN ('string') DO command [command-parameters] FOR /F ["options"] %variable IN (`command`) DO command [command-parameters] file-set is one or more file names. Each file is opened, read and processed before going on to the next file in file-set. Processing consists of reading in the file, breaking it up into individual lines of text and then parsing each line into zero or more tokens. The body of the for loop is then called with the variable value(s) set to the found token string(s). By default, /F passes the first blank separated token from each line of each file. Blank lines are skipped. You can override the default parsing behavior by specifying the optional "options" parameter. This is a quoted string which contains one or more keywords to specify different parsing options. The keywords are: eol=c - specifies an end of line comment character (just one) skip=n - specifies the number of lines to skip at the beginning of the file. delims=xxx - specifies a delimiter set. This replaces the default delimiter set of space and tab. tokens=x,y,m-n - specifies which tokens from each line are to be passed to the for body for each iteration. This will cause additional variable names to be allocated. The m-n form is a range, specifying the mth through the nth tokens. If the last character in the tokens= string is an asterisk, then an additional variable is allocated and receives the remaining text on the line after the last token parsed. usebackq - specifies that the new semantics are in force, where a back quoted string is executed as a command and a single quoted string is a literal string command and allows the use of double quotes to quote file names in file-set.
For a very basic example, lets capture the result of the echo test to a variable. This can be done as follows:
for /f %I in ('echo test') do set OUTPUT="%~I"
Note: The echo test command here could be any executable command (e.g. executing a different batch or any executable file).