This week was the second preliminary laboratory of Operating Systems course in the PUCP. One topic I had to explain to the students was a little introduction to shell scripting.

I told them about an application I made using only Bash Shell Scripting. Why did I use shell scripting? well, because that application had to take a big amount of data (more than 4GB) from two differents databases (oracle & mysql) and do a complex bussiness logic. The solution I provided was filtering the input data with some simple rules (using awk & sed) and discarded unuseful data (aprox 40%). After that, the application used some temporary tables (to do the complex logic) on mysql and got the expected result. It was unncessary to make a compiled program.

BTW, we can do some interesting things with Shell Scripting. For example, a good practice is to give users a feedback that a script is not hung (progress indicator). This is specially useful with long time jobs. 

I will show two kinds of progress indicators:

Simple Progress Indicator

Print a sequence of dots.

 #!/bin/bash
  #
  # Copyright © Abner Ballardo Urco
  # http://www.modlost.net
  #
  
  #
  # Simple Progress Indicator
  #
  function simple_progress_ind {
          # Sleep at least 1 second otherwise this algoritm will consume
          # a lot system resources.
          interval=1
  
          while true
          do
                  echo -ne "."
                  sleep $interval
          done
  }
  
  #
  # Stop distraction
  #
  function stop_progress_ind {
          exec 2>/dev/null
          kill $1
          echo -en "\n"
  }
  
  echo "Simple Progress Indicator"
  echo -n "Processing "
  
  simple_progress_ind &
  pid=$!
  
  /long/time/job/zzZZzz.sh
  
  stop_progress_ind $pid
   
 

Cool Progress Indicator

Print a rotating line.

 #!/bin/bash
  #
  # Copyright © Abner Ballardo Urco
  # http://www.modlost.net
  #
  
  #
  # Cool Progress Indicator
  #
  function cool_progress_ind {
          chars=( "-" "\\" "|" "/" )
          interval=1
          count=0
  
          while true
          do
                  pos=$(($count % 4))
  
                  echo -en "\b${chars[$pos]}"
  
                  count=$(($count + 1))
                  sleep $interval
          done
  }
  
  #
  # Stop progress indicator
  #
  function stop_progress_ind {
          exec 2>/dev/null
          kill $1
          echo -en "\n"
  }
  
  echo "Cool Progress Indicator"
  echo -n "Processing "
  
  cool_progress_ind &
  pid=$!
  
  /long/time/job/zzZZZzz.sh
  
  stop_progress_ind $pid

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