Windows command prompt: Using a variable set in the same line of a one-liner

Question

Okay, I learned that one can use & or && to combine multiple commands into a single line, but it seems that variables that are set

Answer 1

Try the following:

cmd.exe /v /c "set foo=hello, world & echo !foo!"

The /v argument enables delayed variable expansion. This allows you to access variables' values at execution time rather than at parse time (the default). You do this by writing !foo! instead of %foo% (with this /v option turned on).

Instead of passing /v, you can also turn delayed variable expansion on permanently via the registry, which obviously affects the entire system:

[HKEY_LOCAL_MACHINE\Software\Microsoft\Command Processor]
"DelayedExpansion"= (REG_DWORD)
1=enabled 0=disabled (default)