Re: Bash interprets $! as an event

[Dennis Williamson]

History expansion is performed before variable expansion.

>From man bash:

History expansion is performed immediately after  a  complete  line
is  read,  before  the  shell  breaks it into words.

and

!      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).

[emphasis mine]

On Tue, Jul 27, 2010 at 1:01 PM,  <jeremy@nickurak.ca> wrote:
> Configuration Information [Automatically generated, do not change]:
> Machine: x86_64
> OS: linux-gnu
> Compiler: gcc
> Compilation CFLAGS:  -DPROGRAM='bash' -DCONF_HOSTTYPE='x86_64' 
> -DCONF_OSTYPE='linux-gnu' -DCONF_MACHTYPE='x86_64-pc-linux-gnu' 
> -DCONF_VENDOR='pc' -DLOCALEDIR='/usr/share/locale' -DPACKAGE='bash' -DSHELL 
> -DHAVE_CONFIG_H   -I.  -I../bash -I../bash/include -I../bash/lib   -g -O2 
> -Wall
> uname output: Linux figment 2.6.32-24-server #38-Ubuntu SMP Mon Jul 5 
> 10:29:32 UTC 2010 x86_64 GNU/Linux
> Machine Type: x86_64-pc-linux-gnu
>
> Bash Version: 4.1
> Patch Level: 5
> Release Status: release
>
> Description:
>
> Event-catching seems to be catching cases it shouldn't. In particular, $! is 
> caught as an event.
>
> Repeat-By:
>
> This command fails as follows:
>
>> nickurak@woking:~$ sleep 5 & PID=$!; echo "pid is $PID"
>> bash: !: event not found
>
> Adding quotation marks doesn't help:
>
>> nickurak@woking:~$ sleep 5 & PID="$!"; echo "pid is $PID"
>> bash: !": event not found
>
> As a workaround, adding whitespace after the ! fixes it:
>
>> nickurak@woking:~$ sleep 5 & PID=$! ; echo "pid is $PID"
>> [1] 1614
>> pid is 1614
>
> or
>
>> nickurak@woking:~$ sleep 5 & PID="$! "; echo "pid is $PID"
>> [3] 2048
>> pid is 2048
>
>