How to run script continously in background without using crontab

Question

I have a small script that checks certain condition continously and as soon as that condition is met the program should execute. Can this be done. I thought of using crontab where script runs every 5 min but now I want that to be done without crontab

Answer 1

You probably want to create an infinite loop first, then within that loop you probably want to verify your condition or wait a bit. As you did not mention which scripting language you wanted to use, I'm going to write pseudo code for the example. Give us more info about the scripting language, and perhaps also the conditions.

Example in pseudo code:

# Defining a timeout of 1 sec, so checking the condition every second
timeout = 1

# Running in background infinitely
while true do
  # Let's check the condition
  if condition then
    # I got work to do
    ...
  else
    # Let's wait a specified timeout, not to block the system
    sleep timeout
  endif
endwhile

Example in sh with your input code

#!/bin/sh
PATH=/bin:/usr/bin:/sbin:/usr/sbin

# Defining a timeout of 1 hour
timeout=3600

while true
do
  case 'df /tmp' in
    " "[5-9]?%" ") rm -f /tmp/af.*
      ;;
    *)
      sleep $timeout
      ;;
  esac
done

You can then run this script from the shell using 'nohup':

nohup yourscript &