Bash program messages - terminal and log file printing

logSay.sh

# USAGE:
#    say $LEVEL_INFO "This is an" "informational message."
#    #> "This is an informational message."
#
#    sayError "This is an" "error message."
#    #> "ERROR: This is an error message."
#
# LEVELS:
#  In order from highest priority message to lowest:
#    $LEVEL_ALL $LEVEL_ERROR $LEVEL_WARN $LEVEL_INFO $LEVEL_VERBOSE
#       $LEVEL_DEBUG $LEVEL_TRACE $LEVEL_IGNORE
#
# DETAILS:
#  Print a message to the console and/or to a log file. All strings in the
#  message will be concatenated with a space and a newline will be added at
#  the end. The level name + a colon and a space will be prefixed to the
#  message, except (by default) for INFO and VERBOSE console messages. Warning
#  and error console messages will be printed (by default) to STDERR. Escape
#  characters in messages will be translated when printed to the console and
#  left as escape characters when printing to the log file. Messages printed
#  to the log file will also have a timestamp (with no interal spaces) + a
#  space added immediately after the LEVEL: prefix.
#
#  Logging to the console and the screen are independent. By default logging
#  to a file is turned off and messages above INFO are ignored.
#
# GLOBAL PARAMETERS:
#  * SAY_BOUND - At this level and below a message is printed to the console.
#  * LOG_BOUND - At this level and below a message is written to a file.
#  * LOG_FILE - The file to append messages to, created if not existing.
#  * DEFAULT_LEVEL - The default level for a message if not specified.
#  * ERROR_BOUND - At this level and below, console messages print to STDERR.
#  * NO_SAY_INFO - Set to 1 to slip INFO label on console messages.
#  * NO_SAY_VERBOSE - Set to 1 to slip VERBOSE label on console messages.
#
# TODO:
#  * Extract as module
#  * Add functions to change default parameters (Logging and formatting).

# Message level definitions
LEVEL_ALL=-3
LEVEL_ERROR=-2
LEVEL_WARN=-1
LEVEL_INFO=0
LEVEL_VERBOSE=1
LEVEL_DEBUG=2
LEVEL_TRACE=3
LEVEL_IGNORE=4
LEVEL_NAMES=("ALL" "ERROR" "WARN" "INFO" "VERBOSE" "DEBUG" "TRACE" "IGNORE")

# Logging defaults
SAY_BOUND=$LEVEL_INFO
LOG_BOUND=$LEVEL_OFF
ERROR_BOUND=$LEVEL_WARN
DEFAULT_LEVEL=$LEVEL_INFO
LOG_FILE="$0.log"

# Formatting defaults
# TODO: Add color
NO_SAY_INFO=1
NO_SAY_VERBOSE=1

# TODO: Create parameter checking module, migrate this function
function isInt() {
   local val="$1"
   local re='^[-0-9]+$'
   [[ "$val" =~ $re ]]
}

# TODO: Create date/time module, migrate this functions
function timeStamp() {
   local ts=$(date '+%FT%T%z')
   RETVAL="${ts%%??}:${ts: -2}"
}

# Main function
log() {
   # Get message level. If first parameter is not a number, assume that
   # it is part of the message and use the default level.
   local asLevel=$1
   if ! isInt $asLevel ; then
      asLevel=$DEFAULT_LEVEL
   else
      shift
   fi
   
   # Handle out of bound numbers
   [[ $asLevel -lt $LEVEL_ALL ]] && asLevel=$LEVEL_ALL
   [[ $asLevel -gt $LEVEL_IGNORE ]] && asLevel=$LEVEL_IGNORE

   # Want to print to terminal? Handle STDERR vs STDOUT and no-label messages.
   if [[ $asLevel -le $SAY_BOUND ]]; then
      # Want level name?
      if [[ $asLevel == $LEVEL_INFO && $NO_SAY_INFO -eq 1 ]] ||
            [[ $asLevel == $LEVEL_VERBOSE && $NO_SAY_VERBOSE -eq 1 ]]; then
         # Print to stderr or to stdout
         if [[ $asLevel -le $ERROR_BOUND ]]; then
            echo -e "$@" 1>&2
         else
            echo -e "$@"
         fi
      else
         # Print to stderr or to stdout
         if [[ $asLevel -le $ERROR_BOUND ]]; then
            echo -e "${LEVEL_NAMES[((asLevel - LEVEL_ALL))]}:" "$@" 1>&2
         else
            echo -e "${LEVEL_NAMES[((asLevel - LEVEL_ALL))]}:" "$@"
         fi
      fi
   fi

   # Want to print to the log file? Add timestamp and don't translate escapes.
   if [[ $asLevel -le $LOG_BOUND ]]; then
      local ts
      timeStamp
      ts="$RETVAL"
      echo "${LEVEL_NAMES[((asLevel - LEVEL_OFF))]}" "$ts" "$@" 1>>"$LOG_FILE"
   fi
}

# Shortcut alias functions
function logErr()     { log $LEVEL_ERROR   "$@" ; }
function logWarn()    { log $LEVEL_WARNING "$@" ; }
function logInfo()    { log $LEVEL_INFO    "$@" ; }
function logVerbose() { log $LEVEL_VERBOSE "$@" ; }
function logDebug()   { log $LEVEL_DEBUG   "$@" ; }
function logTrace()   { log $LEVEL_TRACE   "$@" ; }