!str Refer to the most recent command starting with str. this is the history expansion behavior. type
man zshexpn
and check 'Event Designators', you will get the answer
An event designator is a reference to a command-line entry in the history list. In the list below, remember that the initial `!' in each item may be changed to another character by setting the histchars parameter.
! Start a history expansion, except when followed by a blank, newline, `=' or `('. If followed immediately by a word designator (see the section `Word Designators'), this forms a history reference with no event designator (see the section `Overview'). !! Refer to the previous command. By itself, this expansion repeats the previous command. !n Refer to command-line n. !-n Refer to the current command-line minus n. !str Refer to the most recent command starting with str. !?str[?] Refer to the most recent command containing str. The trailing `?' is necessary if this reference is to be followed by a modi- fier or followed by any text that is not to be considered part of str. !# Refer to the current command line typed in so far. The line is treated as if it were complete up to and including the word before the one with the `!#' reference. !{...} Insulate a history reference from adjacent characters (if necessary).
