bash-setup

#!/bin/sh
#
# Configure generic bash shell environment.
#
# In WSL environment, make sure prompt and terminal title contains the WSL
# distro name instead of the hostname, which is that of the WSL host.
# Uses the default prompt from Arch and Fedora as starting point.
# Also configure shell options like history, add some aliases etc.
# Do it for all users with a home directory, including root user.
# Assuming running as root, cannot change only for some "current user".
#
# Note: Updates the .bashrc file in individual existing users profile, not the
# global default!
#

# Verify running as root (not relying on sudo which may not be installed yet).
if [ ${EUID:-$(id -u)} -ne 0 ]; then
    echo 'Please run this script as root' >&2
    exit 1
fi

# Verify not running with sudo.
# This would not work, since the environment variables are then stripped to a
# minimum and specifically the WSL_DISTRO_NAME will not be available.
if [ -n "$SUDO_UID" ]; then
    echo 'Please run this script as actual root and not just sudo' >&2
    exit 1
fi

if ! command -v bash > /dev/null 2>&1; then
    if [ "$1" != '--force' ] && [ "$1" != '-f' ]; then
        echo "Bash is not installed" >&2
        echo "To proceed anyway run with argument -f or --force" >&2
        exit 1
    fi
    echo "WARNING: Bash is not installed but proceeding anyway due to argument $1"
fi


# Make sure there is a .bashrc in every existing home directory with some
# proper configuration, as well as a .bash_profile to load it for interactive
# login shells. Also make sure to set the owner, to the same as the home
# directory itself. Normally these will exist, e.g. creating users with
# "useradd --create-home" will put a default .bashrc in place, but there may
# be a home directory created manually that does not contain a .bashrc, and
# e.g. on Alpine bash may be installed when users have already been created.
# Note: Assuming every subdirectory of /home is really a user home, and also
# that the name of the subdirectory always matches the username.

# OLD:
#find /home -mindepth 1 -maxdepth 1 -type d -exec cp --no-clobber /etc/skel/.bashrc {} \; -exec chown --reference={} {}/.bashrc \;
# Make sure root user home directory also has a default .bashrc file,
# as well as .bash_profile to load it for interactive login shells. Normally it
# does not! Assuming we are running as root, current owner should be correct.
#cp --no-clobber /etc/skel/.bash_profile /etc/skel/.bashrc /root
#(find /home -mindepth 2 -maxdepth 2 -type f -name .bashrc -print0 && find /root -mindepth 1 -maxdepth 1 -type f -name .bashrc -print0) | while read -d $'\0' file; do
# ....

(find /home -mindepth 1 -maxdepth 1 -type d -print0 && printf '%s\0' /root) | while read -d $'\0' dir; do
    user=$(basename "$dir")
    echo "Checking user profile ${user}..."

    echo "Checking .bash_profile..."
    file="$dir/.bash_profile"
    if [ ! -f "$file" ]; then
        echo "No existing file"
        if [ -f "/etc/skel/.bash_profile" ]; then
            echo "Copying from skeleton file"
            cp "/etc/skel/.bash_profile" "$dir"
        else
            echo "Creating with hard coded default content"
            # Creating with exact content from /etc/skel/.bash_profile in Arch.
            cat > "$file" << 'EOF'
#
# ~/.bash_profile
#
[[ -f ~/.bashrc ]] && . ~/.bashrc
EOF
        fi
        # Note: The following assumes name of home directory always matches
        # the username. Using chown --reference="$dir" would be safer, but it
        # does not work with BusyBox chown.
        chown "${user}:${user}" "$file"
    else
        echo "Found existing file"
        echo "Skipping: Not checking the existing file and will just assume it is correct"
    fi

    echo "Checking .bashrc..."
    file="$dir/.bashrc"
    if [ ! -f "$file" ]; then
        echo "No existing file"
        if [ -f "/etc/skel/.bashrc" ]; then
            echo "Copying from skeleton file"
            cp /etc/skel/.bashrc "$dir"
        else
            echo "Creating with hard coded default content"
            # Creating with exact content from /etc/skel/.bashrc in Arch.
            # We could have merged in all changes below to get the complete
            # file immediately, but we do it to easier keep track of the origin.
            cat > "$file" << 'EOF'
#
# ~/.bashrc
#

# If not running interactively, don't do anything
[[ $- != *i* ]] && return

alias ls='ls --color=auto'
alias grep='grep --color=auto'
PS1='[\u@\h \W]\$ '
EOF
        fi
        # Note: Same as for .bash_profile above!
        chown "${user}:${user}" "$file"
    else
        echo "Found existing file"
    fi

    # Configure shell prompt for WSL
    # Commenting out any existing assignment of PS1 variable in .bashrc, and
    # adds a new where the WSL distro name is included in the prompt.
    if [ -z "$WSL_DISTRO_NAME" ]; then
        echo "Skipping shell prompt for WSL: Not in a WSL environment"
    else
        # Alternative 1: Default prompt with just \h replaced by ${WSL_DISTRO_NAME}
        # Assuming default is:
        #   PS1='[\u@\h \W]\$ '
        # Creating a new value where ${WSL_DISTRO_NAME} instead of \h:
        #   PS1='[\u@${WSL_DISTRO_NAME} \W]\$ '
        # And then also modify terminal title correspondingly, from something like
        # this which seems to be default, where syntax is "ESC]0;stringBEL" to set
        # window title to string but not icon (change from value 0 to 1 for only icon,
        # 2 for only title, 0 means both, although don't seem to make any difference),
        # with lowercase \w for showing current dir full path, while shell prompt as
        # specified above uses uppercase \W to show only the basename:
        #    \[\e]0;\u@\h:\w\a\]
        # To this:
        #    \[\e]0;\u@${WSL_DISTRO_NAME}:\w\a\]
        #prompt="PS1='\\[\\e]0;\\u@\${WSL_DISTRO_NAME}:\\w\\a\\][\\u@\${WSL_DISTRO_NAME} \\W]\\$ '"

        # Alternative 2: More customized prompt with colors:
        if [ "$user" = "root" ]; then
            # The prompt string to insert. Could also be used to match as fixed
            # string, with 'grep --quiet --line-regexp --fixed-strings "$prompt"',
            # but that is not valid in BusyBox grep.
            prompt="PS1='\\[\\e]0;\\u@\${WSL_DISTRO_NAME}:\\w\\a\\]\\[\\e[01;36m\\]\\u\\[\\e[01;30m\\]@\\[\\e[01;32m\\]\${WSL_DISTRO_NAME} \\[\\e[01;34m\\]\\W \\[\\e[01;31m\\]\\$\\[\\e[00m\\] '"
            # Regex to match any existing, in basic (BRE) syntax, which works
            # with 'grep -q "$prompt"', and therefore also supported with
            # BusyBox grep. The combination of regex escaping necessary with
            # this syntax, and shell double-quote escaping on top of a string
            # that already contains many special characters makes it very
            # complex:
            # 1: Sequences like \e, \u, \w, \a are not valid escape sequences.
            # grep's behavior is undefined — some versions treat \e as literal
            # e (ignoring the backslash), others warn and ignore it. So you
            # cannot use \\ in a double-quoted string to match a literal \ when
            # followed by these letters, because the shell reduces \\ to \, and
            # grep then warns about and ignores the \ in \e, matching only e.
            # The solution is to use a character class [\\] in the double-
            # quoted string, which the shell reduces to [\], and inside a
            # character class \ is just a literal character with no special
            # meaning, so it reliably matches a literal \.
            # 2: Every [ in the pattern — whether it's meant to start a
            # character class or match a literal bracket — is interpreted as
            # opening a character class. So [01;36m] is not "literal [01;36m]",
            # it's a character class containing 0, 1, ;, 3, 6, m followed by a
            # literal ]. The solution is to write every literal [ as [\[] — a
            # character class containing only [, which matches a literal [.
            # Also $ has the same problem — it's an end-of-line anchor outside
            # a character class, so literal \$ in the file needs [\\][$] in the
            # double-quoted string ([\\] becomes [\] matching \, and [$] matches
            # literal $).
            prompt_regex="^PS1='[\\][\\[][\\]e]0;[\\]u@\${WSL_DISTRO_NAME}:[\\]w[\\]a[\\]][\\][\\[][\\]e[\\[]01;36m[\\]][\\]u[\\][\\[][\\]e[\\[]01;30m[\\]]@[\\][\\[][\\]e[\\[]01;32m[\\]]\${WSL_DISTRO_NAME} [\\][\\[][\\]e[\\[]01;34m[\\]][\\]W [\\][\\[][\\]e[\\[]01;31m[\\]][\\][$][\\][\\[][\\]e[\\[]00m[\\]] '\$"
            #echo "$prompt" | grep "$prompt_regex"
            #printf '%s\n' $prompt_regex
        else
            prompt="PS1='\\[\\e]0;\\u@\${WSL_DISTRO_NAME}:\\w\\a\\]\\[\\e[01;36m\\]\\u\\[\\e[01;30m\\]@\\[\\e[01;32m\\]\${WSL_DISTRO_NAME} \\[\\e[01;34m\\]\\W \\[\\e[01;33m\\]\\$\\[\\e[00m\\] '"
            prompt_regex="^PS1='[\\][\\[][\\]e]0;[\\]u@\${WSL_DISTRO_NAME}:[\\]w[\\]a[\\]][\\][\\[][\\]e[\\[]01;36m[\\]][\\]u[\\][\\[][\\]e[\\[]01;30m[\\]]@[\\][\\[][\\]e[\\[]01;32m[\\]]\${WSL_DISTRO_NAME} [\\][\\[][\\]e[\\[]01;34m[\\]][\\]W [\\][\\[][\\]e[\\[]01;33m[\\]][\\][$][\\][\\[][\\]e[\\[]00m[\\]] '\$"
        fi
        if grep -q "$prompt_regex" "$file"; then
            echo "Skipping shell prompt for WSL: Already configured"
        else
            echo "Updating shell prompt for WSL"
            sed -i -r 's/^(\s*PS1=.*)$/#\1/' "$file"
            printf '%s\n' "$prompt" >> "$file"
        fi
        unset prompt prompt_regex
    fi

    # Configure shell history
    # - Append local history to file instead of overwriting, to keep history from multiple parallel sessions.
    # - Do not record repeated commands more than once, and do not record commands prefixed with space.
    # - Record max 1000 entries in memory (bash default is 500 if not overridden by global config)
    # - Read/write max 2000 entries from/to file (bash default is to match history size if not overridden).
    # Note: Originally used 'grep --quiet --line-regexp --fixed-strings "pattern"' for matching, but this is not compatible
    # with BusyBox, so changed it to 'grep -q "^HISTCONTROL=ignoreboth$"' which should be equivalent and work anywhere.
    if grep -q "^shopt -s histappend$" "$file"; then
        echo "Skipping histappend shell option: Already configured"
    else
        echo "Adding histappend shell option"
        echo "shopt -s histappend" >> "$file"
    fi

    # Define variables
    for def in \
        "HISTCONTROL=ignoreboth" \
        "HISTSIZE=1000" \
        "HISTFILESIZE=2000"
    do
        name="${def%%=*}" # %%=* strips from the first = to the end (the name)
        #value="${def#*=}" # #*= strips up to and including the first = (the value)
        if grep -q "^${def}$" "$file"; then
            echo "Skipping variable ${def}: Already defined"
        else
            old=$(grep "^${name}=" "$file")
            if [ -n "$old" ]; then
                echo "Commenting out existing variable ${old}"
                sed -i -r "s/^(\\s*(export\\s+)?${name}=.*)$/#\\1/" "$file"
            fi
            unset old
            echo "Adding variable ${def}"
            echo "$def" >> "$file"
        fi
    done
    unset def name # Currently unused: value line

    # Define aliases
    # - ls alias for automatic colored output by default (already exists by default in Arch)
    # - grep alias for automatic colored output by default (does not exist by default)
    # TODO:
    # - pacman alias for automatic colored output by default (does not exist by default)
    #   - Automatic colored output can also be enabled by option Color in /etc/pacman.conf
    # - diff alias for automatic colored output by default (does not exist by default)
    #   - This assumes package diffutils has been installed, which is not by default.
    #
    for def in \
        "ls=ls --color=auto" \
        "grep=grep --color=auto"
    do
        name="${def%%=*}" # %%=* strips from the first = to the end (the name)
        value="${def#*=}" # #*= strips up to and including the first = (the value)
        line="alias ${name}='${value}'"
        if grep -q "^${line}$" "$file"; then
            echo "Skipping ${line}: Already defined"
        else
            old=$(grep "^alias ${name}=" "$file")
            if [ -n "$old" ]; then
                echo "Commenting out existing ${old}"
                sed -i -r "s/^(\\s*alias\\s+${name}=.*)$/#\\1/" "$file"
            fi
            unset old
            echo "Adding ${line}"
            printf '%s\n' "${line}" >> "$file"
        fi
    done
    unset def name value line

    unset user file
done
unset dir