( https://linux.die.net/man/1/bash )

Event Designators
An event designator is a reference to a command line entry in the history list. 

!     Start a history substitution, except when followed by a blank, newline, carriage return, = or ( (when the extglob shell option is enabled using the shopt builtin). 

!n      Refer to command line n. 

!-n     Refer to the current command line minus n. 

!!     Refer to the previous command. This is a synonym for '!-1'. 

!string     Refer to the most recent command starting with string. 

!?string[?]     Refer to the most recent command containing string. The trailing ? may be omitted if string is followed immediately by a newline. 

^ string1 ^ string2 ^     Quick substitution. Repeat the last command, replacing string1 with string2. Equivalent to ''!!:s/string1/string2/'' (see Modifiers below). 

!#     The entire command line typed so far. 


Word Designators 
Word designators are used to select desired words from the event. A : separates the event specification from the word designator. It may be omitted if the word designator begins with a ^, $, *, -, or %. Words are numbered from the beginning of the line, with the first word being denoted by 0 (zero). Words are inserted into the current line separated by single spaces. 

0 (zero)     The zeroth word. For the shell, this is the command word. 

n     The nth word. 

^     The first argument. That is, word 1. 

$     The last argument. 

%     The word matched by the most recent '?string?' search. 

x-y     A range of words; '-y' abbreviates '0-y'. 

*     All of the words but the zeroth. This is a synonym for '1-$'. It is not an error to use * if there is just one word in the event; the empty string is returned in that case. 

x*     Abbreviates x-$. 

x-     Abbreviates x-$ like x*, but omits the last word. 
If a word designator is supplied without an event specification, the previous command is used as the event. 


Modifiers 

After the optional word designator, there may appear a sequence of one or more of the following modifiers, each preceded by a ':'. 

h     Remove a trailing file name component, leaving only the head. 

t     Remove all leading file name components, leaving the tail. 

r     Remove a trailing suffix of the form .xxx, leaving the basename. 

e     Remove all but the trailing suffix. 

p     Print the new command but do not execute it. 

q     Quote the substituted words, escaping further substitutions. 

x     Quote the substituted words as with q, but break into words at blanks and newlines. 

s/old/new/     Substitute new for the first occurrence of old in the event line. Any delimiter can be used in place of /. The final delimiter is optional if it is the last character of the event line. The delimiter may be quoted in old and new with a single backslash. If & appears in new, it is replaced by old. A single backslash will quote the &. If old is null, it is set to the last old substituted, or, if no previous history substitutions took place, the last string in a !?string[?] search. 

&     Repeat the previous substitution. 

g     Cause changes to be applied over the entire event line. This is used in conjunction with ':s' (e.g., ':gs/old/new/') or ':&'. If used with ':s', any delimiter can be used in place of /, and the final delimiter is optional if it is the last character of the event line. An a may be used as a synonym for g. 

G     Apply the following 's' modifier once to each word in the event line.