Re: Bash and the PS1 environment variable [was: grep: show matching line from pattern file]

[Will Mengarini <seldon@eskimo.com>]

* David Christensen <dpchrist@holgerdanske.com> [22-06/02=Th 18:01 -0700]:
>On 6/2/22 17:12, Will Mengarini wrote:
>> * David Christensen [22-06/02=Th 15:50 -0700]:
>>> On 6/2/22 15:13, Will Mengarini wrote:
>
>>>> In this transcript, the number before the prompt-ending '$' is $?:
>>>> --------------------------------
>>>> debian/pts/4 bash3 ~ 14:56 0$perl -e 'open "gweeblefleep" || die'
>>>> debian/pts/4 bash3 ~ 14:57 0$perl -e 'open "gweeblefleep" or die'
>>>> Died at -e line 1.
>>>> debian/pts/4 bash3 ~ 14:57 2$
>>>> --------------------------------
>>>
>>> What is your shell?  PS1?
>>
>> The shell is Bash 5.1.4.
>> PS1="\\h/${TTY#/dev/} \\s$SHLVL \\w \\A \$?\\\$"
>
> Interesting.
>
> This is my daily driver:
>
> 2022-06-02 17:38:55 dpchrist@laalaa ~
> $ cat /etc/debian_version ; uname -a ; dpkg-query -W bash
> 11.3
> Linux laalaa 5.10.0-14-amd64 #1 SMP Debian 5.10.113-1 (2022-04-29) x86_64
> GNU/Linux
> bash	5.1-2+b3
>
> This is my PS1. '\u' does not work on all of Debian, FreeBSD,
> Cygwin, and macOS, so the expansion of ${USER} is inserted
> between two string literals when .profile runs and sets PS1:
>
> 2022-06-02 17:39:09 dpchrist@laalaa ~
> $ grep PS1 .profile
> export PS1='\n\D{%Y-%m-%d %H:%M:%S} '${USER}'@\h \w\n\$ '
> #export PS1='\n\D{%Y-%m-%d %H:%M:%S} \u@\h \w\n\$ '
>
> Testing your PS1:
>
> 2022-06-02 17:45:03 dpchrist@laalaa ~
> $ PS1="\\h/${TTY#/dev/} \\s$SHLVL \\w \\A \$?\\\$"
> laalaa/ -bash1 ~ 17:45 0$
>
> The snippet '${TTY#/dev/}' seems to produce ' -' on my computer.
> How does your computer produce 'pts/4 ' and what does it mean?

'pts/4' is an abbreviation of '/dev/pts/4', pseudoterminal 4.

TTY is `tty`; it's been so long I'd forgotten that's not available in
all shells.  You should have the 'tty' program; it's in coreutils.

> Is there a reason why you are using
> double quotes, rather than single quotes?

So I can interpolate stuff like ${TTY#/dev/}.  In your case,
you'll need to set TTY=`tty` before setting PS1, so Bash
can use string substitution to remove '/dev/' from it.