Your code sample isn't quite right.
[read stdin] returns a string (not a list of strings), which is parsed as a list when you try to loop over it. The parsing breaks the string into a list of words, so the second loop is redundant. The parsing could fail if the input file isn't valid list syntax (unmatching {}'s). [split _] makes it safe.
foreach word [split [read stdin]] {
if [string match *ing $word] { puts $word }}