Prompt sample: Debian chroot environment

When you chroot in Debian, bash shows the chroot environment in the prompt:

```bash

...

if [ -z "${debian_chroot:-}" ] && [ -r /etc/debian_chroot ]; then
    debian_chroot=$(cat /etc/debian_chroot)
fi

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

...
```

This is the effect:

```
(chroot_env) user@host:~#
```

It is useful when chrooting, since usually the hostname remains the same and thus you can't distinguish where you are.

1 files changed, 55 insertions, 0 deletions

diff --git a/share/tools/web_config/sample_prompts/debian_chroot.fish b/share/tools/web_config/sample_prompts/debian_chroot.fish
new file mode 100644
index 00000000..d800c744
--- /dev/null
+++ b/share/tools/web_config/sample_prompts/debian_chroot.fish
@@ -0,0 +1,55 @@
+# name: Debian chroot
+# author: Maurizio De Santis
+
+function fish_prompt --description 'Write out the prompt, prepending the Debian chroot environment if present'
+
+        # Just calculate these once, to save a few cycles when displaying the prompt
+        if not set -q __fish_prompt_hostname
+                set -g __fish_prompt_hostname (hostname|cut -d . -f 1)
+        end
+
+        if not set -q __fish_prompt_normal
+                set -g __fish_prompt_normal (set_color normal)
+        end
+
+        if not set -q __fish_prompt_chroot_env
+                set -g __fish_prompt_chroot_env (set_color yellow)
+        end
+
+        # Set variable identifying the chroot you work in (used in the prompt below)
+        if begin; not set -q debian_chroot; and test -r /etc/debian_chroot; end
+                set debian_chroot (cat /etc/debian_chroot)
+        end
+        if begin; not set -q __fish_debian_chroot_prompt; and set -q debian_chroot; and test -n $debian_chroot; end
+                set -g __fish_debian_chroot_prompt "($debian_chroot)"
+        end
+
+        # Prepend the chroot environment if present
+        if set -q __fish_debian_chroot_prompt
+                echo -n -s "$__fish_prompt_chroot_env" "$__fish_debian_chroot_prompt" "$__fish_prompt_normal" ' '
+        end
+
+        switch $USER
+
+                case root
+
+                if not set -q __fish_prompt_cwd
+                        if set -q fish_color_cwd_root
+                                set -g __fish_prompt_cwd (set_color $fish_color_cwd_root)
+                        else
+                                set -g __fish_prompt_cwd (set_color $fish_color_cwd)
+                        end
+                end
+
+                echo -n -s "$USER" @ "$__fish_prompt_hostname" ' ' "$__fish_prompt_cwd" (prompt_pwd) "$__fish_prompt_normal" '# '
+
+                case '*'
+
+                if not set -q __fish_prompt_cwd
+                        set -g __fish_prompt_cwd (set_color $fish_color_cwd)
+                end
+
+                echo -n -s "$USER" @ "$__fish_prompt_hostname" ' ' "$__fish_prompt_cwd" (prompt_pwd) "$__fish_prompt_normal" '> '
+
+        end
+end