Appending to PROMPT_COMMAND

ahtoot · 09-29-2010, 10:44 PM

I have the following as my $PROMPT_COMMAND in .bashrc:

Code:

PROMPT_COMMAND='
if [ $TERM = "screen" ]; then
 MYPWD="${PWD/#$HOME/~}"
 [ ${#MYPWD} -gt 20 ] && MYPWD=..${MYPWD:${#MYPWD}-18}
 echo -n -e "\033k$MYPWD\033\\"
fi
'

I am trying to append items to my PROMPT_COMMAND in another script/on command line. If I do the following:

Code:

export PROMPT_COMMAND="$PROMPT_COMMAND && ls"

bash has a syntax error and complains of unexpected token near &&.
But if I change the following in .bashrc

Code:

PROMPT_COMMAND='
if [ $TERM = "screen" ]; then
 MYPWD="${PWD/#$HOME/~}"
 [ ${#MYPWD} -gt 20 ] && MYPWD=..${MYPWD:${#MYPWD}-18}
 echo -n -e "\033k$MYPWD\033\\"
fi && ls
'

I get no error.

I've echoed the value of $PROMPT_COMMAND in both cases and their output is exactly the same.

Any tips? Thanks.

Meson · 09-29-2010, 11:08 PM

It probably has to do with the fact that you already have quotes inside the original prompt command.

grail · 09-29-2010, 11:33 PM

I am curious what you expect to happen?

If you did the following on the command line:

Code:

PROMPT_COMMAND="$PROMPT_COMMAND && ls"

And now perform an echo, all that has happened is '&& ls' gets appended to the string.

The questions then becomes, what is processing $PROMPT_COMMAND?

ahtoot · 09-30-2010, 01:08 AM

Quote:

Originally Posted by grail

I am curious what you expect to happen?

If you did the following on the command line:

Code:

PROMPT_COMMAND="$PROMPT_COMMAND && ls"

And now perform an echo, all that has happened is '&& ls' gets appended to the string.

The questions then becomes, what is processing $PROMPT_COMMAND?

bash is processing $PROMPT_COMMAND
http://tldp.org/HOWTO/Bash-Prompt-HOWTO/x264.html

I've solved it, I had to put the last quote on the same line as the last fi

Code:

PROMPT_COMMAND='
if [ $TERM = "screen" ]; then
 MYPWD="${PWD/#$HOME/~}"
 [ ${#MYPWD} -gt 20 ] && MYPWD=..${MYPWD:${#MYPWD}-18}
 echo -n -e "\033k$MYPWD\033\\"
fi'

Now if someone can tell me why the previous version didn't work..

Code:

PROMPT_COMMAND='
if [ $TERM = "screen" ]; then
 MYPWD="${PWD/#$HOME/~}"
 [ ${#MYPWD} -gt 20 ] && MYPWD=..${MYPWD:${#MYPWD}-18}
 echo -n -e "\033k$MYPWD\033\\"
fi
'

Edit: Maybe because && can't start on a newline?

catkin · 09-30-2010, 01:12 AM

Because the fi command needs to be terminated -- by a ; or by a newline.