Question

I have a windows cmd batch file that uses a variable, but everywhere that variable is used after setting it is failing.

Here is my batch script:

@echo off

if exist Transactions.csv (
    set datestr=%date:~10,4%%date:~7,2%%date:~4,2%%time:~0,2%%time:~3,2%%time:~6,2%
    rename Transactions.csv Transactions-%datestr%.csv
    curl -s -o curl.log --form upload=@Transactions-%datestr%.csv http://192.168.5.217/test_upload.php
    set datestr=
)

The file gets renamed to “Transactions-.csv”, and the curl command works OK because it’s sending the file as is, but I’d like it to properly rename the file.

If I comment out the echo off line, this is what I get back:

if exist Transactions.csv (
    set datestr=20112206112720
    rename Transactions.csv Transactions-.csv
    curl -s -o curl.log --form upload=@Transactions-.csv http://192.168.5.217/test_upload.php
    set datestr=
)

Note the missing areas where %datestr% should be.

Any ideas why these variables are not properly being parsed?

Answer 1

When you have a block of commands enclosed in parentheses, the entire block is parsed before its first command executes. That means, all the %var% expressions inside that block are replaced with their values at that time. That’s why you could see nothing in place of %datestr% when you ran the script with @echo off commented out.

So your decision to move the body of the IF statement outside the brackets was right.

Another solution to that would be to use delayed expansion:

@echo off

setlocal EnableDelayedExpansion

if exist Transactions.csv (
    set datestr=!date:~10,4!!date:~7,2!!date:~4,2!!time:~0,2!!time:~3,2!time:~6,2!
    rename Transactions.csv Transactions-!datestr!.csv
    curl -s -o curl.log --form upload=@Transactions-!datestr!.csv http://192.168.5.217/test_upload.php
    set datestr=
)

As you can see, the delayed expansion mode is introduced with the setlocal EnableDelayedExpansion command. Note also the change of syntax: ! instead of % denote the delayed expansion of the corresponding variable/expression. When delayed expansion is enabled, you can still use % for immediate expansion, where appropriate.