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h1. Generalised messaging function

{{toc}}

h1. Called function

finalise: called after generating an error message

h1. Function msg

<pre>

#!/bin/bash   <- Does nothing but triggers editor syntax highlighting

# Copyright (C) 2013 Charles Atkinson

#

# This program is free software; you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation; either version 2 of the License, or

# (at your option) any later version.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

# GNU General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program; if not, write to the Free Software

# Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA

#--------------------------

# Name: msg

# Purpose: generalised messaging interface

# Arguments:

#    $1 class: D, E, I or W indicating Debug, Error, Information or Warning

#    $2 message text

#    $3 logger control. Optional

#       If "logger" then also send class I messages with logger (to syslog)

#       If "no_logger" then do not also send class  W and E messages with

#       logger (to syslog).

# Global variables read: none

# Output: information messages to stdout; the rest to stderr

# Returns: 

#   Does not return (calls finalise) when class is E for error

#   Otherwise returns 0

#--------------------------

function msg {

    local buf class i logger_flag logger_msg message_text prefix

    local -r regex='^(|(logger)|(no_logger))$'

    local -r max_logger_chars=100000

    # Process arguments

    # ~~~~~~~~~~~~~~~~~

    class="${1:-}"

    message_text="${2:-}"

    [[ ! ${3:-} =~ $regex ]] && msg E "Programming error: invalid ${FUNCNAME[0]} third argument '${3:-}' (does not match regex $regex)"

    # Class-dependent set-up

    # ~~~~~~~~~~~~~~~~~~~~~~

    logger_flag=$false

    case "$class" in  

        D ) 

            [[ ! $debugging_flag ]] && return

            prefix='DEBUG: '

            [[ ${3:-} = logger ]] && logger_flag=$true

            ;;  

        E ) 

            error_flag=$true

            prefix='ERROR: '

            [[ ${3:-} != no_logger ]] && logger_flag=$true

            ;;  

        I ) 

            prefix=

            [[ ${3:-} = logger ]] && logger_flag=$true

            ;;  

        W ) 

            warning_flag=$true

            prefix='WARN: '

            [[ ${3:-} != no_logger ]] && logger_flag=$true

            ;;  

        * ) 

            msg E "msg: invalid class '$class': '$*'"

    esac

    # Write to syslog

    # ~~~~~~~~~~~~~~~

    if [[ $logger_flag ]]; then

        preamble=<whatever is appropriate for your app>

        logger_msg=("$prefix$message_text")

        if ((${#logger_msg}>max_logger_chars)); then

            unset logger_msg

            logger_msg+=("${prefix}Message too big (>$max_logger_chars characters)")

            logger_msg+=('The message is split into pieces:')

            buf=$message_text

            while ((${#buf}>0))

            do

                logger_msg+=("${buf:0:$max_logger_chars}")

                buf=${buf:$max_logger_chars}

            done

        fi  

        for ((i=0;i<${#logger_msg[*]};i++))

        do  

            buf=$(logger -t "$preamble" -- "${logger_msg[i]}" 2>&1)

            [[ $buf != '' ]] && msg W "${FUNCNAME[0]}: problem writing to syslog: $buf"

        done

    fi

    # Write to stdout or stderr

    # ~~~~~~~~~~~~~~~~~~~~~~~~~

    # Which is to log if such redirection is set up, as is usual

    message_text="$(date "$log_date_format") $prefix$message_text"

    if [[ $class = I ]]; then

        echo "$message_text"

    else

        echo "$message_text" >&2

        if [[ $class = E ]]; then

            [[ ! $finalising_flag ]] && finalise 1 

        fi

    fi  

    return 0

}  #  end of function msg

</pre>