batch file - What happens with IF command when I pipe to it?

Question

Here is my script:

   @echo off
    echo.|if defined 1 geq 1 echo 1 is geq than 1
    echo.|if defined 2 gtr 100 echo 2 is gtr than 100

    echo.|if 1 gtr gtr 100 echo 1 is gteater than 100
    echo.|if 100 lss gtr 100 echo 100 is gteater and the same time less than 100

the output is :

1 is geq than 1
2 is gtr than 100
1 is gteater than 100
100 is gteater and the same time less than 100

What is going with IF command?

Answer 1

The batch parser concatenates the first tokens after the IF.

To gain an insight you can use the cmdcmdline variable.

From a batch file

@echo off
echo pipe | if defined 1 geq 1 echo %%cmdcmdline%%

In the output you can see that defined and 1 are concatenated, so this is the cause for the strange results

C:Windowssystem32cmd.exe /S /D /c" if defined1 geq 1 echo %cmdcmdline%"

When you test this from the command line you need to modify the %%cmdcmdline%% to %^cmdcmdline% as the cmd-parser works a bit different with percent expansions.