5.34.111.3 Special Characters [ ], { }, and \

Sometimes square brackets ([ ]) are part of the command syntax. In these cases, you must either enclose the open and closed square brackets characters with curly brackets ({ }) or precede the open and closed square brackets ([ ]) characters with a backslash (\). If you do not, you will get an error message.

For example:

pin_assign -port {LFSR_OUT[0]} -pin 15 or

pin_assign -port LFSR_OUT\[0\] -pin 180

Tcl commands are case sensitive. However, their arguments are not.