Example: String length

Example: String length

The home page directly greets any wiki visitors with this unusual and slightly cryptic piece of batch code to determine the length of a string:

1    set "string=hello world"
2    echo %string%>temp.txt
3    for /f %%f in ("temp.txt") do ( set /a length=%%~zf - 2 )
4    del temp.txt
5    echo length of string is %length%

added line numbers for reference

But what actually happens here?

1. In line 1, we declare a variable called string and set it to the string value hello world. Note the missing whitespace around the assignment operator ( = ): no whitespace can be used before the assignment operator. Whitespace after the operator would be incorporated into the string. Also note the quotation marks around the entire assignment: this is required when assigning a string that contains spaces.
2. In line 2, we print out the value of variable string (wrapping the variable in percent signs for variable expansion), but redirect the output destination from the console to a new file called temp.txt. Again, notice the missing whitespace around the redirection operator ( > ), which would otherwise be interpreted to be part of the string.
3. In line 3, we use the /f switch for loop, which loops through the file contents of the file "temp.txt" and stores each line in the for-loop variable %%f. On each iteration of the for loop (in this case, only one, as the file contains a single line), we declare a variable called length and set it to %%~zf and subtract 2 from it. The expression %%~zf takes the for-loop variable %%f and modifies it using the in-fix ~z, which stands for the file size of %%f in bytes. Two bytes need to be subtracted from that file size, as they are automatically included in the file by Windows. Note the /a switch of the set command, which needs to be used to allow arithmetic operations on a variable.
4. Finally, we delete the no longer required tempfile on line 4 and print out the length of the string to the console.