log in shell scripts

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Tags: website

In some scenarios, we need to store shell script console output to a log file. In log4j, we can define two appenders, one for ConsoleAppender and the other one for FileAppender. In console, we can use FIFO (named pipe) to redirect the output to log files. Unfortunately, in sh/ksh, we have to do it manually.

Here is one implementation:

Step 1: define a utility shell function

shell_functions.sh

startLogging(){
  if [ -p "/tmp/$$.fifo" ]; then
    then 1
  fi

  logginTo=$1
  mkfifo /tmp/$$.fifo
  exec 3>&1 4>&2

  tee "$1" < /tmp/$$.fifo >&3 & tpid=$!

  exec > /tmp/$$.fifo 2>&1

  echo "Logging started to $1" >&2
}

stopLogging(){
  if [ -p "/tmp/$$.fifo" ]; then
    echo "logfile written to ${loggingTo}" >&2
    exec 1>&3 3>&- 2>&4 4>&-
    wait $tpid 
    rm /tmp/$$.fifo
  fi
}

Step 2: You can put it in a central place for all caller shell scripts.

in setenv.sh

if [ $VERBOSE -ne 0 ]; then
  if [ -z "${RT_SCRIPT_LOGDIR}" ]; then
    RT_SCRIPT_LOGDIR="${APP_LOG_DIR}/$(basename "$0").$(date
    +"%Y%m%d_%H%M%S").log"
  fi
  startLogging "${RT_SCRIPT_LOGDIR}"
fi

Step 3: then include both utility script and common ‘setenv.sh’ in execution script.

in a real calling script

BASEDIR=$(cd $(dirname $0); pwd)

# pull in common shell functions
. $(dirname "$0")/shell_functions.sh

# stop logging on exit
trap "stopLogging" EXIT

. $(dirname "$0"/setenv.sh

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