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bash script + cron (how to wait for condition to start)

Posted on 2006-11-15
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Last Modified: 2011-08-18
I have a bash script which is scheduled as a cronjob to run each day. However, I want it to wait for an ftp update before starting. So it should it first check if a file has been updated on an ftp server, if so then start, if not then wait an hour and try again. After 3 hours if it's still not updated then don't run today.

I already have the script to check for an ftp update. I just need to know how to wait for it to return true. Any ideas?
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Question by:itcdr
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Expert Comment

by:slyong
ID: 17950907
If you script to check for ftp update, use "exit $x" where x is your exit status, then you should be able to track the exit status from your second script.
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by:itcdr
ID: 17950972
Yes, but how do I set it so if it's not ready to wait an hour before checking again. And after 3 times (3 hours) quit if there is still no update.
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slyong earned 500 total points
ID: 17951102
Just try to write a sample script for you...

#!/bin/sh
# check.sh just return an exit status assuming this is your ftp update script...
exit 1

#!/bin/bash
# test.sh test if ftp update script status code is 0
for i in 1 2 3
do
  ./check.sh
  if [ $? -eq 0 ]
  then
    echo $i "yes"
    break;
  fi
  echo $i "no"
  sleep 1h
done
exit 0
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Author Comment

by:itcdr
ID: 17951216
I didn't realize there was a sleep program in linux. I just want to make sure that doing something like this the program won't just timeout and quit before it retries. What do you think?
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Expert Comment

by:slyong
ID: 17951436
hmm.. sleep don't really have a timeout problem.  I am not aware of any problem with that.  Normally I know that we have problem that a script doesn't finish on time and we have to break it (force timeout in the bash script) but not the other way around.  So, this should be fine.
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Author Comment

by:itcdr
ID: 17951475
Sounds good. Here is my new startup script I will set for my update.

#!/bin/bash
checkFTP() {
  #My code to check for FTP update, return 1 if there was one
}

for i in 1 2 3
do
  checkFTP
  if [ $? -eq 1 ]; then ./my_script; exit; fi
  sleep 1h
done



Thanks for your help!
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LVL 24

Expert Comment

by:slyong
ID: 17951500
No worries.  Thanks for the points
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