How to check which terminal emulator is being currently used?

You can get the terminal emulator name, by grepping the parents process name. Therefore it works with every terminal emulator.

In bash, zsh, etc.:

basename "/"$(ps -f -p $(cat /proc/$(echo $$)/stat | cut -d \  -f 4) | tail -1 | sed 's/^.* //')

With fish-shell:

basename "/"(ps -f -p (cat /proc/(echo %self)/stat | cut -d \  -f 4) | tail -1 | sed 's/^.* //')

Try this:

echo $TERM

This is more authoritative, but could be messed up by your programs. However on mine, it says xterm and on ttys it says linux, which I think stands for Linux Console.

This function should do the job:

container() {
    pid=$$
    while true; do
        pid=$(ps -h -o ppid -p $pid 2>/dev/null)
        case $(ps -h -o comm -p $pid 2>/dev/null) in
        (gnome-terminal) echo "Running in gnome terminal";return;;
        (xterm) echo "Running in xterm";return;;
        (rxvt) echo "Running in rxvt";return;;
        (python) if [ ! -z "$(ps -h -o args -p $pid 2>/dev/null | grep guake)" ]; then echo "Running in Guake"; return; fi ;;
        esac
        [[ $(echo $pid) == 1 ]] && break
    done
}
container