Re: ! history expansion occurs within arithmetic substitutions

[Dale R. Worley]

Andreas Schwab <schwab@linux-m68k.org> writes:
>> More troublesome, I think, are several variable substitutions which
>> include "!" followed by a name.  But I doubt they're used much in
>> interactive mode.
>
> The history expansion is smart enough to not interfere with ${!var}.

Yes...  Also, the same magic seems to apply to $!, even if it isn't at
the end of a word.  The manual page should probably mention the criteria
for suppressing history expansion there, whatever they are.  Perhaps
"history expansion is not triggered by the history expansion character
when it is part of a variable reference" is unambiguous enough;
quoting (anti-recognition) of ! and $ have the same rules, I think.

I was checking the manual page again, and I think it would be clearer
(certainly, would be to me) if a paragraph break was inserted as
follows:

       History expansion is performed immediately after  a  complete  line  is
       read,  before  the shell breaks it into words, and is performed on each
       line individually without taking quoting on  previous  lines  into  ac‐
       count.   It  takes place in two parts.  The first is to determine which
       line from the history list to use during substitution.  The  second  is
       to  select  portions  of  that line for inclusion into the current one.
       The line selected from the history is the event, and  the  portions  of
       that  line that are acted upon are words.  Various modifiers are avail‐
       able to manipulate the selected words.

       The line is broken  into  words
       in  the same fashion as when reading input, so that several metacharac‐
       ter-separated words surrounded by quotes are considered one word.  His‐
       tory  expansions are introduced by the appearance of the history expan‐
       sion character, which is ! by default.  Only backslash (\)  and  single
       quotes  can  quote the history expansion character, but the history ex‐
       pansion character is also treated as quoted if it immediately  precedes
       the closing double quote in a double-quoted string.

The first part talks mostly about what history substitutions *do* and
the second talks about how they are triggered, which isn't a
continuation of the first part.  Indeed, I think that it would be
clearer to rearrange them into:

       History expansion is performed immediately after a complete line
       is read, before the shell breaks it into words, and is performed
       on each line individually without taking quoting on previous
       lines into account.  The line is broken into words in the same
       fashion as when reading input, so that several
       metacharacter-separated words surrounded by quotes are considered
       one word.  History expansions are introduced by the appearance of
       the history expansion character, which is ! by default.  Only
       backslash (\) and single quotes can quote the history expansion
       character, but the history expansion character is also treated as
       quoted if it immediately precedes the closing double quote in a
       double-quoted string.

       History expansion takes place in two parts.  The first is to
       determine which line from the history list to use during
       substitution.  The second is to select portions of that line for
       inclusion into the current one.  The line selected from the
       history is the event, and the portions of that line that are
       acted upon are words (as determined above).  Various modifiers
       are available to manipulate the selected words.

Dale