Here we have our nightly database backup script that runs in a cron job:

Notice the use of:

• if/else structures;
• for loop structures;
• branching on file existance check; and
• the use of strong (') and week (") quotes.

backup_databases:

  #!/bin/bash 
  #  Backup,  
  #  Move to off-line to Backup Server, and
  #  Vacuum 
  # 03-Jun-2003  -dvl
  # 08-Dec-2004  -dvl brought to viddev1
  # 24-May-2005  -im  group write permission to db dump file
  # 11-Oct-2005  -dvl reworked to use archive.pl
  
  # Tweak these as need be ----------------
  
    dblist="prod1 prod2"
    do_schema=1
    do_nonsales=1
    do_sales=1;   
    years="2006" # 2003 2002 2001 2000"
    vacuum=1
  
  # ----------------------------------------
  
  logdir=/var/log
  bkupdir=/backup
  storage_dir="/backups/$HOSTNAME"
  weekday=`date|cut -c1-3`
  
  # function: copy_to_storage  
  # must split files greater than 2gig due to microsoft limitation
  
  gig=1073741824
  gig1_5=1610612736 # 1.5 Gig
  let two_gig=$gig*2
  function copy_to_storage () {
      db=$1;
      file_extension=$2
      logfile=$3
      dump_file=${bkupdir}/${db}_${file_extension}
      storage_file=${storage_dir}/${db}_${weekday}_$file_extension
      size=$(ls -l $dump_file |cut -d' ' -f6)
      if (( $size < $two_gig )) ; then
         cp -v $dump_file $storage_file 2>&1 |tee -a $logfile
      else
         split --verbose -b$gig1_5 $dump_file $storage_file 2>&1 |tee -a $logfile
      fi
  }
  
  if [ ! -d ${storage_dir} ] ; then
    mount_netbackup
  fi
  
  
  if (( $vacuum )) ; then 
     opts='';
  else
     opts='-b'; # backup only (no vacuum)
  fi
    
  for db in $dblist; do
    logfile=$logdir/${db}_backup.log
  
    if (( $do_schema )) ; then
       su -l postgres -s /bin/bash -c "archive.pl -nd $db -t schema"
       copy_to_storage $db schema_dump.gz $logfile
    fi
  
    if (( $do_nonsales )) ; then
       su -l postgres -s /bin/bash -c "archive.pl $opts -nd $db -t nonsales"
       copy_to_storage $db nonsales_data.gz $logfile
    fi
  
    if (( $do_sales )) ; then
       for year in $years; do
          su -l postgres -s /bin/bash -c "archive.pl $opts -nd$db -tsales -y$year"
          copy_to_storage $db sales_${year}_data.gz $logfile
       done
    fi
  
  done;