see if a list contains a particular element
lsearch [mode] list pattern
This command searches the elements of list to see
if one of them matches pattern. If so, the
command returns the index of the first matching element.
If not, the command returns -1. The mode
argument indicates how the elements of the list are to be
matched against pattern; it must have one of the
The list element must contain exactly the same string as
pattern is a glob-style pattern which is matched
against each list element using the same rules as the
string match command.
pattern is treated as a regular expression and
matched against each list element using the same rules as
the regexp command.