generate serial numbers

get_serial_number.sh

#!/bin/bash
## returns a serial number based on a file
## can be used for programs requiring a running id
## different apps can have their own serial numbers
## different folders can have their serial number file
# == PROCESS OPTIONS ==
Revision="0.1"
Date="2009-11-06"
arg0=$(basename "$0")
istart=1
increment=1
irestart=999999
MYDIR=~/bin
VERBOSE_FLAG=0
app="GENERAL"

usage()
{
    sed -e 's/^    //' <<EndUsage
    Usage: $arg0 [OPTIONS]
    OPTIONS: 
             -a application name (separate counter for different applications
             -s start
             -i increment
             -r reset
             -d directory for serial_number file
    Try '$arg0 -h' for more information.
EndUsage
    exit 1
}
help()
{
    sed -e 's/^    //' <<EndUsage
    $arg0
    Returns a serial number based on a file 'serial_number'
    Can be used for programs requiring a running id
    Different apps can have their own serial numbers
        $arg0 -a ACCOUNTS
    different folders can have their serial number file
        $arg0 -d /Users/ram/projects
    Without application option, returns one serial number sequence to all callers
        $arg0 
        
EndUsage
}


while getopts hVvd:a:s:i:r: flag
do
    case "$flag" in
    (h) help; exit 0;;
    (V) echo "$arg0: version $Revision ($Date) Author: rkumar"; exit 0;;
    (v) VERBOSE_FLAG=1;;
    (a) app="$OPTARG";;
    (i) increment="$OPTARG";;
    (s) istart="$OPTARG";;
    (r) irestart="$OPTARG";;
    (d) MYDIR="$OPTARG";;
    (*) usage;;
    esac
done
shift $(($OPTIND - 1))
file=$MYDIR/serial_numbers
[ -f "$file" ] || echo "GENERAL:0" > "$file"
## user mentioned an app
[ -z "$app" ] || {
    [ $VERBOSE_FLAG -gt 0 ] && echo "$arg0: App mentioned $app"
   ## check if app exists, if not initialize
   exists=$(grep "^$app" "$file")
   [ -z "$exists" ] && {
       [ $VERBOSE_FLAG -gt 0 ] && echo "$arg0: No entry for $app, creating one"
      let result=$istart+$increment
      echo "$app:$result" >> "$file"
      echo $istart
      exit 0
   }
   [ $VERBOSE_FLAG -gt 0 ] && echo "$arg0: Entry for app found:>> $exists"
   ## extract counter
   ctr=`expr "$exists" : '.*:\([0-9]\+\)'`
   let result=$ctr+$increment
   ## update serial number in file
   sed -i.bak -e "/$app/s/:$ctr$/:$result/" $file
   echo $ctr
   exit 0

}

#[ $VERBOSE_FLAG -gt 0 ] && echo "$arg0: No app mentioned, general case"
[ $VERBOSE_FLAG -gt 0 ] && echo "$arg0: Should not cme here !!"