string map is replacing ? with a space

string map uses glob-style pattern matching which means that ? is a special character meaning "any one character". If you need to match a literal ? you need to escape it:

 

 

string map "adserver/impression/pid=$pid/oid=$oid/rand=$rand/\?click ad.imp\?pid=$pid&oid=$oid&rand=$rand/\?pclk"

 

 

The same would be true of * [ and ]

 

 

http://www.tcl.tk/man/tcl8.4/TclCmd/string.htm