fdswap.sh

#!/bin/bash
#
# Swap/Roll a file handle between processes.
#
# Posted at https://groups.google.com/forum/#!topic/alt.hackers/0ZMsMc5DvUw
#
# Usage:
#
#    fdswap.sh <old logfile>    <new logfile> [optional pids]
#    fdswap.sh /var/log/logfile /tmp/logfile  [pids]
#
# Author: Robert McKay
# Date: Tue Aug 14 13:36:35 BST 2007

src=$1
dst=$2
shift
shift
pids=$*

for pid in ${pids:=$(/sbin/fuser $src)}; do
  echo "${src} has ${pid} using it..."
  (
    echo "attach ${pid}"
    echo 'call open("'${dst}'", 66, 0666)'
    for ufd in $(ls -l /proc/${pid}/fd | grep ${src}\$ | awk '{print $9;}'); do
      echo 'call dup2($1, '${ufd}')'
    done
    echo 'call close($1)'
    echo 'detach'
    echo 'quit'
    sleep 3
  ) | gdb -q -x -
done