grabfd

#!/bin/sh
##
## Grab stdin/stdout/stderr from another process
## Copyright (c) 2014 SATOH Fumiyasu @ OSS Technology Corp., Japan
##
## License: GNU General Public License version 3
##

## Inspired by:
##	http://yudoufu.hatenablog.jp/entry/2014/02/06/001440
##	http://qiita.com/kawaz/items/96af6fa59fdf999b94bd

set -u

pdie() {
  echo "$0: ERROR: $1"
  exit ${2-1}
}

cmd_usage="Usage: $0 [OPTIONS] PID

Options:
 -w, --wait
  Wait for process termination (default: Wait if stdout and/or stderr is tty)
 -W, --no-wait
  Do not wait for process termination
 -i, --stdin
  Grab process's stdin too (default: stdout and stderr only)
"

o_rdonly=0x0000
o_wronly=0x0001
if [ x"`uname`" = x"Linux" ]; then
  o_append=02000
else
  o_append=0x0008
fi

unset wait_f
stdin_f=''

while [ $# -gt 0 ]; do
  case "$1" in
  --wait|-w)
    wait_f='set'
    ;;
  --no-wait|-W)
    wait_f=''
    ;;
  --stdin|-i)
    stdin_f='set'
    ;;
  --)
    break
    ;;
  -*)
    pdie "Unknown option: $1"
    ;;
  *)
    break
    ;;
  esac
  shift
done

if [ -n "$stdin_f" ] && [ -t 0 ] || [ -t 1 ] || [ -t 2 ]; then
  wait_f='set'
else
  wait_f=''
fi

if [ $# -lt 1 ] || [ $# -gt 2 ]; then
  echo "$cmd_usage"
  exit 1
fi

pid="$1"; shift
kill -0 "$pid" || pdie "No such process ID: $pid"
if [ -n "${1:+set}" ]; then
  pid2="$1"; shift
  kill -0 "$pid" || pdie "No such process ID: $pid2"
else
  pid2="$$"
fi

if [ -d "/proc/$pid2/fd" ]; then
  stdin="/proc/$pid2/fd/0"
  stdout="/proc/$pid2/fd/1"
  stderr="/proc/$pid2/fd/2"
else
  if [ "$pid2" -ne "$$" ]; then
    pdie "Cannot attach to another process's stdio on this platform"
  fi
  tty=`tty` || pdie "Tty not detected"
  stdin="$tty"
  stdout="$tty"
  stderr="$tty"
fi

shift $#

## FIXME: Only gdb 7.0+ support --eval-command option
if [ -n "$stdin_f" ]; then
  set -- "$@" --eval-command="print close(0)"
  set -- "$@" --eval-command="print open(\"$stdin\", $o_rdonly)"
fi
set -- "$@" --eval-command="print close(1)"
set -- "$@" --eval-command="print open(\"$stdout\", $o_wronly|$o_append)"
set -- "$@" --eval-command="print close(2)"
set -- "$@" --eval-command="print open(\"$stderr\", $o_wronly|$o_append)"
set -- "$@" --eval-command="quit"

gdb_out=`gdb --batch --quiet -p "$pid" "$@" 2>&1`

if [ $? -ne 0 ]; then
  echo "$gdb_out" 1>&2
  pdie "gdb failed"
fi

if [ -z "$wait_f" ]; then
  exit 0
fi

if type pwait >/dev/null 2>&1; then
  pwait "$pid"
elif type procwait >/dev/null 2>&1; then
  procwait "$pid"
else
  ## pwait(1) emulation

  cd "/proc/$pid" 2>/dev/null || exit 0

  if type inotifywait >/dev/null 2>&1; then
    inotifywait='set'
  else
    inotifywait=
  fi

  while :; do
    if [ -n "$inotifywait" ]; then
      inotifywait --quiet --event close_nowrite exe >/dev/null || sleep 1
    else
      sleep 1
    fi
    if ! cd . 2>/dev/null; then
      break
    fi
  done
fi

exit 0