[SOLVED] Bash prompt - getting history command number in PROMPT_COMMAND

Gerard Lally · 04-15-2017, 06:39 PM

In PS1 I'm able to get the history command number using one of bash's internal variables: \!

In the attached screenshot you can see this number is updated when \! is used in PS1 (next to user name).

I prefer to have this number on the line above the prompt, which is produced by PROMPT_COMMAND. How is that achieved? I can't use \! there, and if I use $HISTCMD instead, the job number remains stuck at 1, as you can see in the screenshot.

Below are the prompt_align and .bashrc scripts.

prompt_align

Code:

print_pre_prompt () 
{ 
PS1L=" ${HOSTNAME}"
PS1R=$PWD
if [[ $PS1R/ = "$HOME"/* ]]
then
PS1R=\~${PS1R#$HOME}
fi
printf "\n%s%$(($COLUMNS-${#PS1L}))s\n%s%$(($COLUMNS-${#HISTCMD}-2))s\n" "$PS1L" "${SHELL##*/} | $TERM | $(tty) " "[$HISTCMD]" "[$PS1R]"
}
PROMPT_COMMAND=print_pre_prompt

.bashrc

Code:

source ~/prompt_align
PROMPT_COMMAND=print_pre_prompt
export PS1='[\!][\u]\$ '

norobro · 04-15-2017, 10:17 PM

I'm a little confused by your use of the term "job number". From the bash manual page:

Quote:

HISTCMD
The history number, or index in the history list, of the current command.
...

If that is what you want try this:

In prompt_align change the last new line to a carriage return and don't print HISTCMD:

Code:

printf "\n%s%$(($COLUMNS-${#PS1L}))s\n%s%$(($COLUMNS-${#HISTCMD}-2))s\r" "$PS1L" "${SHELL##*/} | $TERM | $(tty) " "[$PS1R]"

Then add a line feed to your prompt:

Code:

export PS1='[\!]\n[\u]\$ '

I tried the above and it seemed to work.

HTH

Gerard Lally · 04-16-2017, 06:59 AM

Quote:

Originally Posted by norobro

I'm a little confused by your use of the term "job number". From the bash manual page:
If that is what you want try this:

In prompt_align change the last new line to a carriage return and don't print HISTCMD:

Code:

printf "\n%s%$(($COLUMNS-${#PS1L}))s\n%s%$(($COLUMNS-${#HISTCMD}-2))s\r" "$PS1L" "${SHELL##*/} | $TERM | $(tty) " "[$PS1R]"

Then add a line feed to your prompt:

Code:

export PS1='[\!]\n[\u]\$ '

I tried the above and it seemed to work.

HTH

That does indeed put the history command number above the user name but it also gets rid of the right-aligned path.

norobro · 04-16-2017, 08:24 AM

Unless I'm missing something it looks like the following produces what you want on my box.

prompt_align:

Code:

$ cat prompt_align 
print_pre_prompt () 
{ 
PS1L="${HOSTNAME}"
PS1R=$PWD
if [[ $PS1R/ = "$HOME"/* ]]
then
PS1R=\~${PS1R#$HOME}
fi
printf "\n%s%$(($COLUMNS-${#PS1L}))s\n%$(($COLUMNS))s\r" "$PS1L" "${SHELL##*/} | $TERM | $(tty) " "[$PS1R]"
#printf "\n%s%$(($COLUMNS-${#PS1L}))s\n" "$PS1L" "${SHELL##*/} | $TERM | $(tty) " 
#printf "%*s\r%s\n\%s\$ " "$(tput cols)" "$PWD" "$HISTCMD"
}
PROMPT_COMMAND=print_pre_prompt

In .bashrc

Code:

source ~/temp/prompt_align
PROMPT_COMMAND=print_pre_prompt
export PS1='[\!]\n[\u]\$ '

Gerard Lally · 04-16-2017, 08:45 AM

Quote:

Originally Posted by norobro

Unless I'm missing something it looks like the following produces what you want on my box.

printf "\n%s%$(($COLUMNS-${#PS1L}))s\n%$(($COLUMNS))s\r" "$PS1L" "${SHELL##*/} | $TERM | $(tty) " "[$PS1R]"
}
PROMPT_COMMAND=print_pre_prompt[/code]

Perfect! Thank you. In your earlier post you had a %s before the second COLUMNS arithmetic expansion. Removing that in your second post solved the problem. See attached.

Why does \r work when \n doesn't?

norobro · 04-16-2017, 09:07 AM

Quote:

Originally Posted by Gerard Lally

In your earlier post you had a %s before the second COLUMNS arithmetic expansion.

Sorry, I typed that in instead of c/p'ing.

Quote:

Why does \r work when \n doesn't?

You're probably to young to remember manual typewriters and teletypes but that is where I learned the term carriage return.

A carriage return ("\r"), in this case, moves the cursor to the first column on the same line. So HISTCMD "[\!]" is printed on the same line as the PWD and then on a new line "[\u]\$ " is printed. A line feed ("\n") would move the cursor to the first column on the next line.
https://en.wikipedia.org/wiki/Carriage_return

Gerard Lally · 04-16-2017, 09:13 AM

Quote:

Originally Posted by norobro

Sorry, I typed that in instead of c/p'ing.

You're probably to young to remember manual typewriters and teletypes but that is where I learned the term carriage return.

50 next month so not too young at all! Thanks for the explanation. It makes sense of course.