There are a few more topics that we should look at in this chapter. Suppose you want to be alerted when a running process ends on your system.
Here's a script that notifies the user when the specified process ends. Note that there are other ways to do this task, this is just one approach.
#!/bin/sh # # 5/3/2017 # echo "script12 - Linux Scripting Book" if [ $# -ne 1 ] ; then echo "Usage: script12 process-directory" echo " For example: script12 /proc/20686" exit 255 fi FN=$1 # process directory i.e. /proc/20686 rc=1 while [ $rc -eq 1 ] do if [ ! -d $FN ] ; then # if directory is not there echo "Process $FN is not running or has been terminated." let rc=0 else sleep 1 fi done echo "End of script12" exit 0
To see this script in action run the following commands:
- In a terminal, run
script9 - In another terminal run
ps auxw | grep script9. The output will be something like this:guest1 20686 0.0 0.0 106112 1260 pts/34 S+ 17:20 0:00 /bin/sh ./script9 guest1 23334 0.0 0.0 103316 864 pts/18 S+ 17:24 0:00 grep script9
- Use the process ID from
script9(in this case20686) and use it as the parameter to runscript12:$ script12 /proc/20686
You may let it run for a bit if you want. Eventually go back to the terminal that is running script9 and terminate it with Ctrl + C. You will see script12 output a message and then also terminate. Feel free to experiment with this one as it has a lot of important information in it.
You may notice that in this script I used a variable, rc, to determine when to end the loop. I could have used the break command as we saw earlier in this chapter. However, using a control variable (as it's often called) is considered to be a better programming style.
A script like this can be very useful when you have started a command and then it takes longer than you expected for it to finish.
For example, a while back I started a format operation on an external 1 TB USB drive using the mkfs command. It took a few days to complete and I wanted to know exactly when so that I could continue working with the drive.