Bash – How to change bash prompt string in current bash session

bashhostnameprompt

I have a following bash prompt string:

root@LAB-VM-host:~# echo "$PS1"
${debian_chroot:+($debian_chroot)}\u@\h:\w\$ 
root@LAB-VM-host:~# hostname 
LAB-VM-host
root@LAB-VM-host:~#

Now if I change the hostname from LAB-VM-host to VM-host with hostname command, the prompt string for this bash session does not change:

root@LAB-VM-host:~# hostname VM-host
root@LAB-VM-host:~#

Is there a way to update hostname part of bash prompt string for current bash session or does it apply only for new bash sessions?

Best Answer

Does Debian really pick up a changed hostname if PS1 is re-exported, as the other answers suggest? If so, you can just refresh it like this:

export PS1="$PS1"

Don't know about debian, but on OS X Mountain Lion this will not have any effect. Neither will the explicit version suggested in other answers (which is exactly equivalent to the above).

Even if this works, the prompt must be reset separately in every running shell. In which case, why not just manually set it to the new hostname? Or just launch a new shell (as a subshell with bash, or replace the running process with exec bash)-- the hostname will be updated.

To automatically track hostname changes in all running shells, set your prompt like this in your .bashrc:

export PS1='\u@$(hostname):\w\$ '

or in your case:

export PS1='${debian_chroot:+($debian_chroot)}\u@$(hostname):\w\$ '

I.e., replace \h in your prompt with $(hostname), and make sure it's enclosed in single quotes. This will execute hostname before every prompt it prints, but so what. It's not going to bring the computer to its knees.

Related Solutions

Bash – I changed the hostname, why is the bash PS1 prompt unchanged

I'm answering my own question, in light of previous answers by Keith and Warren, and the actual resolution. The perceived problem was "I changed my hostname, why is my bash PS1 prompt unchanged?" The actual problem was "Why has my system reverted to its old hostname on reboot?"

The answer in this particular case was: DHCP is configured to override local settings.

An Effective Way to Change the Hostname

The following is applicable to Ubuntu, ymmv.

Change the persistent hostname by editing the file /etc/hostname.
```
echo 'mynewhostname' | sudo tee /etc/hostname
```
To change the hostname for the running system use the hostname command. Without Step 1 this would be reset on reboot. It makes sense to use the value you just set:
```
sudo hostname -F /etc/hostname
```
or its equivalent:
```
sudo hostname `cat /etc/hostname`
```
Set the fully qualified domain name (FQDN) in /etc/hosts.

Excerpt:
```
127.0.0.1    mynewhostname.mydomainname.com    mynewhostname
```
Check if the machine is running a DHCP client. In addition to IP address, a DHCP server may well override settings like hostname and DNS resolution. A "cloud" hosting service might do this so the image of a machine on disk can be reused several times without editing configuration files.

If it exists, edit the DHCP client configuration file /etc/default/dhcpcd to comment out the SET_HOSTNAME directive:
```
#SET_HOSTNAME='yes'
```
When possible, reboot the system and check the name has changed with:
```
hostname
```

Step 4 was news to me and caught me out. I thought it would be useful to document the whole process in this answer. That step is courtesy of (Linode) my hosting service's instructions which I really should have read properly.

Bash – Is there a way to customize “Programmable Completion” in the current session

In the bash_completion mechanism it's the bash function _filedir_xspec() that is responsible for filename and dirname completions. This funtion can be found in the script /etc/bash_completion.

You can edit that function and add a line that contains your regex. For example use this function (it's a copy of the original function):

_filedir_xspec()
{
    local IFS cur xspec

    IFS=$'\n'
    COMPREPLY=()
    _get_comp_words_by_ref cur

    _expand || return 0

    # get first exclusion compspec that matches this command
    xspec=$( awk "/^complete[ \t]+.*[ \t]${1##*/}([ \t]|\$)/ { print \$0; exit }" \
        "$BASH_COMPLETION" )
    # prune to leave nothing but the -X spec
    xspec=${xspec#*-X }
    xspec=${xspec%% *}

    local -a toks
    local tmp

    toks=( ${toks[@]-} $(
        compgen -d -- "$(quote_readline "$cur")" | {
        while read -r tmp; do
            # see long TODO comment in _filedir() --David
            printf '%s\n' $tmp
        done
        }
        ))

    # Munge xspec to contain uppercase version too
    eval xspec="${xspec}"
    eval xspec="!*.txt" #<---- HERE add your regex, that's the only line changed
    local matchop=!
    if [[ $xspec == !* ]]; then
        xspec=${xspec#!}
        matchop=@
    fi
    [[ ${BASH_VERSINFO[0]} -ge 4 ]] && \
        xspec="$matchop($xspec|${xspec^^})" || \
        xspec="$matchop($xspec|$(printf %s $xspec | tr '[:lower:]' '[:upper:]'))"

    toks=( ${toks[@]-} $(
        eval compgen -f -X "!$xspec" -- "\$(quote_readline "\$cur")" | {
        while read -r tmp; do
            [ -n $tmp ] && printf '%s\n' $tmp
        done
        }
        ))
    [ ${#toks[@]} -ne 0 ] && _compopt_o_filenames
    COMPREPLY=( "${toks[@]}" )
}

Notice the new part at line 32:

eval xspec="!*.txt"

This statement is later used in compgen to remove all entries, that do not match the regular expression. I wouldn't recommend to edit the file /etc/bash_completion. Instead make a new file with the content above and source the file if needed:

source /path/to/file

Now, all commands/applications in the shell, that where completed by the function _filedir_xspec(), complete now only with *.txt filenames.

Best Answer

Related Solutions

Bash – I changed the hostname, why is the bash PS1 prompt unchanged

Bash – Is there a way to customize “Programmable Completion” in the current session

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