bash: avoid subprocess spawns during interactive shell startup

On the live image, a fork/exec during login-shell startup can stall the
shell before its first prompt. Replace command substitutions with pure
builtins in the startup path:

- bash.bashrc: read /etc/redox_chroot with the 'read' builtin instead of
  $(cat ...)
- profile: derive the root prompt from EUID/USER/LOGNAME (set by
  login(1)) instead of $(id -u)
- skel/.bashrc: disable lesspipe and dircolors eval (both spawn
  subprocesses); keep the ls --color=auto alias

recipes/shells/bash/etc/bash.bashrc

@@ -11,8 +11,11 @@
 shopt -s checkwinsize
 
 # TODO: redox_chroot
+# Read the file with the `read` builtin instead of `$(cat ...)`: a command
+# substitution here fork/execs a subprocess, and a spawn during interactive
+# shell startup can stall the shell on the live image before its first prompt.
 if [ -z "${redox_chroot:-}" ] && [ -r /etc/redox_chroot ]; then
-    redox_chroot=$(cat /etc/redox_chroot)
+    read -r redox_chroot < /etc/redox_chroot 2>/dev/null || redox_chroot=
 fi
 
 # set a fancy prompt (non-color, overwrite the one in /etc/profile)

recipes/shells/bash/etc/profile

@@ -9,7 +9,12 @@ if [ "${PS1-}" ]; then
       . /etc/bash.bashrc
     fi
   else
-    if [ "$(id -u)" -eq 0 ]; then
+    # Do NOT spawn a subprocess here (the old `$(id -u)` command substitution).
+    # A login shell sources this file before drawing its first prompt; on Redox
+    # a process spawn during that window can stall, hanging the shell before it
+    # is ever usable. Use the shell/login-provided EUID or USER instead — both
+    # are set by login(1) — so this stays a pure builtin test with no fork/exec.
+    if [ "${EUID-}" = 0 ] || [ "${USER-}" = root ] || [ "${LOGNAME-}" = root ]; then
       PS1='# '
     else
       PS1='$ '

recipes/shells/bash/etc/skel/.bashrc

@@ -26,7 +26,9 @@ shopt -s checkwinsize
 #shopt -s globstar
 
 # make less more friendly for non-text input files, see lesspipe(1)
-[ -x /usr/bin/lesspipe ] && eval "$(SHELL=/bin/sh lesspipe)"
+# lesspipe disabled: `$(lesspipe)` spawns a subprocess during shell startup,
+# which can stall the shell on the live image before its first prompt.
+#[ -x /usr/bin/lesspipe ] && eval "$(SHELL=/bin/sh lesspipe)"
 
 # set a fancy prompt (non-color, unless we know we "want" color)
 case "$TERM" in
@@ -58,7 +60,9 @@ unset color_prompt force_color_prompt
 
 # enable color support of ls and also add handy aliases
 if [ -x /usr/bin/dircolors ]; then
-    test -r ~/.dircolors && eval "$(dircolors -b ~/.dircolors)" || eval "$(dircolors -b)"
+    # dircolors disabled: `$(dircolors -b)` spawns a subprocess during shell
+    # startup, which can stall the shell on the live image before its prompt.
+    # test -r ~/.dircolors && eval "$(dircolors -b ~/.dircolors)" || eval "$(dircolors -b)"
     alias ls='ls --color=auto'
     #alias dir='dir --color=auto'
     #alias vdir='vdir --color=auto'