Chet Ramey <chet.ra...@case.edu> writes:
>> While declaring a string literal across multiple lines, a line starting
>> with the ^ character is resulting in some sort of quick substitution
>> processing.
>
> This is a standard form of history expansion, described in the man page.
I just checked. Certainly, the use of ^ is mentioned in the man page,
but it isn't very clearly described, unfortunately. In particular, ^ is
only active at the beginning of a line, which doesn't seem to be
described at all. The only relevant passages seem to be:
histchars
The two or three characters which control history expansion and
tokenization (see HISTORY EXPANSION below). The first character
is the history expansion character, the character which signals
the start of a history expansion, normally `!'. The second
character is the quick substitution character, which is used as
shorthand for re-running the previous command entered, substiâ
tuting one string for another in the command. The default is
`^'. [...]
Note that this doesn't mention that ^ has to appear at the beginning of
a line. The other passage is:
Event Designators
An event designator is a reference to a command line entry in the
history list. Unless the reference is absolute, events are relative
to the current position in the history list.
! Start a history substitution, except when followed by a blank,
newline, carriage return, = or ( (when the extglob shell opâ
tion is enabled using the shopt builtin).
!n Refer to command line n.
!-n Refer to the current command minus n.
!! Refer to the previous command. This is a synonym for `!-1'.
!string
Refer to the most recent command preceding the current posiâ
tion in the history list starting with string.
!?string[?]
Refer to the most recent command preceding the current posiâ
tion in the history list containing string. The trailing ?
may be omitted if string is followed immediately by a newline.
If string is missing, the string from the most recent search
is used; it is an error if there is no previous search string.
^string1^string2^
Quick substitution. Repeat the previous command, replacing
string1 with string2. Equivalent to ``!!:s^string1^string2^''
(see Modifiers below).
!# The entire command line typed so far.
A quick read suggests that "^string1^string2^" is an event designator
which presumably is "the thing that follows !", leading one to guess
that the syntax is "!^string1^string2^". A more careful reading
reveals that the list of event designators all include the initial !,
which suggests that "^string1^string2^" alone is the correct syntax.
That's correct, but it doesn't reveal that it must be at the beginning
of a line. Indeed, the ^ form really should be removed from that list
and mentioned as a separate thing.
Dale
