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Add working version of bashrc-forward

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cubernetes 2026-10-01 08:54:28 +02:00
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#!/usr/bin/env bash
#-# Shebang for syntax highlighting
#-# Minimum Bash version on target host: 4.4
bashrc_get () {
#-# Not perfect, but good enough hack for me and quite concise for what it accomplishes
#-# Has some bugs, which is why we have to introduce this bashrc_get and that bashrc_load function, instead
#-# of just embedding it inside the command substitution.
echo "set -v"
#-# Setting BASH_COMPLETION_VERSINFO because nixos likes to hijack your .bashrc to run bash-completion.sh, which
#-# of course fails on remote systems, so we need a way to stop that from happening. Not perfect, but I'll accept the tradeoff.
echo "[ \"\${BASH_COMPLETION_VERSINFO-}\" ] || BASH_COMPLETION_VERSINFO="
#-# There's still a bug in bash at the moment regarding verbose mode not being turned on again after ${ :;}
#-# https://www.mail-archive.com/bug-bash@gnu.org/msg35966.html
#-# Therefore, be careful to use this new command substition syntax until it is fixed upstream!
cat ~/.bashrc
echo "set +v"
}
bashrc_load () {
if [ "$_s" ]; then
#-# Relay .bashrc if it has already been forwarded
: "${_s#*[B]ASH_COMPLETION_VERSINFO=[[:space:]]}"
printf %s "${_%[[:space:]][s]et +v*}"
else
#-# Warning: Your `.bashrc` MUST NOT print any error messages at all!
#-# Additionally, be aware that every time you use bashrc_forward,
#-# the entire `.bashrc` gets executed, so try to make your `.bashrc`
#-# as idempotent as possible. You can also add the string
#-# - ` # bashrc_forward: noreexec`
#-# (leading space mandatory!) the the end of those lines that should not be re-executed, but be aware that this only
#-# works for lines directly inside the `~/.bashrc`, not inside files sourced by `~/.bashrc`.
#-#
#-# If there's lines you don't want to forward at all (e.g. secrets), add the string
#-# - ` # bashrc_forward: ignore`
#-# (leading space mandatory!) to the lines of your `.bashrc` that should not get forwarded!
#-# You may combine `ignore` and `noreexec` like this: ` bashrc_forward: noreexec ignore`.
#-#
#-# The process substition below MUST be a single line. See the command above the call-site of `bashrc_load` to understand why.
2>&1 >/dev/null bash --rcfile <(bashrc_get | grep -v ' # *bashrc_forward: .*\<noreexec\>[ a-z]*$') -ic :
fi |
#-# Removing comments (if marked as such by using #-#) because final `.bashrc` must be
#-# below 131k bytes because of resource limits (`MAX_ARG_STRLEN` on Linux)
grep -v -e '^[[:space:]]*#\+-#' -e ' # *bashrc_forward: .*\<ignore\>[ a-z]*$' |
sed '
s,/nix/store/[^/]\+,,
s,'\'','\''\\'\'''\''\\'\''\\'\'''\'''\''\\'\'''\'',g
'
}
#-# Warning, forwards the entire effective .bashrc, which may include secrets or confidential data.
#-# Everything is provided "AS IS" without any warranty. Use at your own risk.
#-# Without any pipelines and without any external utilies on the remote system (except the shell)*.
#-#
#-# *unless you relay the `.bashrc`, in that case the remote system needs sed, grep, cat and bash.
bashrc_forward () {
printf %s '
_argv_wrap () {
if >/dev/null 2>&1 command -v bash; then
bash -c '\''
if [ "$#" -gt 0 ]; then
builtin exec -- bash "$@"
#-# Newest Bash feature used here is parameter transformation (`${_s@A}`), introduced in Bash 4.4
elif ! ((BASH_VERSINFO[0]>4||(BASH_VERSINFO[0]==4&&BASH_VERSINFO[1]>=4))) 2>/dev/null; then
>&2 echo "Failed to SSH with .bashrc-forwarding, the Bash version is too old."
>&2 echo "Please install Bash 4.4 or newer on the target system and make it available in the PATH."
>&2 echo "Falling back to default login shell: '\''\'\'''\''${SHELL:-${0#-}}'\''\'\'''\''."
builtin exec -l -- "${SHELL:-${0#-}}"
fi
ENV=<(
_s='\''\'\'''\''
set +o posix
#-# In case `$0` is checked by other scripts
BASH_ARGV0=bash
#-# The following host-side command substitution MUST be single line if this file where the bashrc_forward function is defined
#-# is part of the host-side .bashrc. Otherwise the self-inclusion trick with the `set -v; cat ~/.bashrc; set +v` WILL NOT work,
#-# either because of a bug in bash or because of a quirk I do not understand. For some reason, if it is multiline, only the line
#-# where the command substition starts is printed. If there is a trailing backslash, then also the second line is printed. But in
#-# no circumstance will the last line be printed, no matter what amount of trailing backslashes you add.
'"$(bashrc_load)"'
#-# Not universal, but good enough to bash is preferrably invoked as sh so our constructed ENV is loaded.
alias bash="bash -c '\''\'\'''\''\'\''\'\'''\'''\''\'\'''\''exec -a sh bash \"\$@\"'\''\'\'''\''\'\''\'\'''\'''\''\'\'''\'' _"
#-# instead of the sudobash alias, you can also just do `sudo bbrc`. Keeping the `sudobash` alias anyway as an alternative.
#-# Warning: Be careful! sudobash will run YOUR .bashrc with ROOT on the remote system! You may or may not want this!
alias sudobash="ENV_RAW=\$(<\"\$ENV\") sudo --preserve-env=ENV_RAW bash --norc --noprofile -ic '\''\'\'''\''\'\''\'\'''\'''\''\'\'''\''. <(printf %s \"\$ENV_RAW\"); unset -v ENV_RAW; builtin eval \"\$PROMPT_COMMAND\"; builtin exec -a sh bash \"\$@\"'\''\'\'''\''\'\''\'\'''\'''\''\'\'''\'' _"
#-# Using PROMPT_COMMAND instead of DEBUG trap because of speed tradeoffs (DEBUG trap runs way too often)
#-# Also explicitly removing the export flag as to not append needlessly, in case the remote system exported it accidentally.
declare +x PROMPT_COMMAND=${PROMPT_COMMAND:+$PROMPT_COMMAND$'\''\'\'''\''\'\''\'\'''\'''\''\'\'''\''\n'\''\'\'''\''\'\''\'\'''\'''\''\'\'''\''}'\''\'\'''\''\'\''\'\'''\'''\''\'\'''\''
#-# Close stale file descriptor
[[ "${ENV##*/}" =~ ^[0-9]+$ ]] && builtin eval "builtin exec ${ENV##*/}<&-"
#-# Constructs new ENV after every command, thanks to the quine
builtin exec {ENV}< <(
printf %s "${_s@A}
$_s"
)
export ENV="/dev/fd/$ENV"
'\''\'\'''\''\'\''\'\'''\'''\''\'\'''\''
'\''\'\'''\''
printf %s "${_s@A}; $_s"
#-# Suppress the warning `bash: POSIXLY_CORRECT: readonly variable` using a one-shot DEBUG trap
#-# `PS0` and `PROMPT_COMMAND` will not suffice, `PROMPT_COMMAND` runs AFTER the command, therefore
#-# our first command would be interpreted in posix mode (bad), and commands in `PS0` always run in a
#-# subshell that does not affect the parent shell (unless we assume Bash 5.3+, which we do not).
#-# Therefore, the only sensible options for us to get out of posix mode are:
#-# - unset `POSIXLY_CORRECT` and make it readonly. When Bash tries to overwrite it, it fails, keeping the shell out of posix mode
#-# - Run `exec 2> >(stdbuf -o0 tail -n+2)` right here. But this depends on stdbuf and tail, which may or may not exist (and it would be bloated)
#-# - Print the initial prompt early, disable stderr, and restore stderr in `PROMPT_COMMAND` (runs after the inital command) (robs the first command of its stderr)
#-# - use a DEBUG trap to unset POSIXLY_CORRECT before the first command runs
#-# Only the last options seems to satisfy all constraints, albeit less elegant since the DEBUG trap is kinda like a chainsaw for everything.
#-# But we do not want to always disable posix mode, so we need to reset the DEBUG to its original value
echo '\''\'\'''\''
trap '\''\'\'''\''\'\''\'\'''\'''\''\'\'''\''
set +o posix
: "$(trap -p DEBUG)"
: "${_#trap -- }"
: "$(builtin eval echo "${_% DEBUG}.")"
: "${_#*[M]ARKER[[:space:]]}"
: "${_%.}"
trap "${_:--}" DEBUG; : MARKER'\''\'\'''\''\'\''\'\'''\'''\''\'\'''\''$'\''\'\'''\''\'\''\'\'''\'''\''\'\'''\''\n'\''\'\'''\''\'\''\'\'''\'''\''\'\'''\''"$(
: "$(trap -p DEBUG)"
: "${_#trap -- }"
builtin eval printf %s "${_% DEBUG}"
)" DEBUG
'\''\'\'''\''
) \
builtin exec -a sh bash -l
#-# Note for the exec above: `ENV` is read if and only if bash is invoked as `sh` (or `-sh`), which we enforce using `exec -a sh ...`.
#-# Additionally, when invoked just as `sh`, it never reads `~/.bashrc` (or `/etc/bash.bashrc`), because of the implicit posix mode.
#-# When invoked as a login shell however (either by having a leading dash in `argv[0]` or with `--login/-l`),
#-# then `/etc/profile` and the one user startup file (in this precedence order: `~/.bash_profile`, `~/.bash_login`, `~/.profile`, in posix mode only the last)
#-# are loaded. `/etc/profile` usually loads `/etc/bash.bashrc` and the user startup file usually loads `~/.bashrc`.
#-# The system bashrc (`SYS_BASHRC`, usually `/etc/bash.bashrc`) is disabled by default and only some distros enable it, like Debian:
#-# - https://sources.debian.org/src/bash/5.3-4/debian/patches/deb-bash-config.diff#L32
#-# Also, you might think `BASH_ENV` would be more appropriate, but it only works with a non-interactive Bash shell, so it is not an option.
'\'' "$(command -v bash)" "$@"
else
if [ "$#" -gt 0 ]; then
exec "${SHELL:-${0#-}}" "$@"
else
>&2 echo "Failed to SSH with .bashrc-forwarding, could not find Bash binary."
>&2 echo "Please install Bash 4.4 or newer on the target system and make it available in the PATH."
>&2 echo "Falling back to default shell (warning, possibly not a login shell anymore!): '\''${SHELL:-${0#-}}'\''."
#-# Using generic `exec` call instead of fancy `exec -l --` because we cannot assume that we are inside Bash.
#-# For example, the exec builtin from the Dash shell does not support any options at all, not even `--`.
exec "${SHELL:-${0#-}}" || { _status=$?; >&2 echo "Failed to run shell '\''${SHELL:-${0#-}}'\''"; exit "$_status"; }
fi
fi
}
_argv_wrap \
'
}
#-# Special aliases that play nicely with my `bash-abbr` bash plugin. The leading `*` means they expand
#-# anywhere in the command line (as long as they start a word). Like global aliases in zsh.
#-# Allows you to do these kinds of things:
#-# - `docker container run --rm -itu1000 ubuntu bbrc` -> the `bbrc` expands to `bash -c "$(bashrc_forward)"` -> starts ubuntu container as ubuntu user with my bashrc
#-# -> inside the container:
#-# - either `sudobash` (escalates to root and keeps my bashrc)
#-# - or just `sudo bbrc` -> uses the same trick to forward bashrc to root shell
#-# - `ssh host tbrc` -> `tbrc` expands to `-t "$(bashrc_forward)"` -> ssh to host with my bashrc
#-# - `su another_user -c brc` -> expands to `su another_user -c "$(bashrc_forward)"` -> switch to another user but keep the bashrc (e.g. in containers)
alias brc='*"$(bashrc_forward)"'
alias bbrc='*sh -c "$(bashrc_forward)"'
alias tbrc='*-t "$(bashrc_forward)"'