CODEWITHSUNDEEP
shellunix
Raghvendra Gupta
Raghvendra Gupta

Reputation: 73

Best Option for resumable script

I am writing a script that executes around 10 back-end processes in sequence, depending on if the previous process was executed without any errors.

Now let's assume the scenario, in which lets say 5th process failed and script came out. But I want to code it in a way such that, when next time user runs it(after removing the error because of which script exited last time), he should be able to run from 5th process onwards and not again from 1st process.

To be more specific, assume following is the script:

Script Starts
Process1
if [ $? -eq 0 ] then
Process2
if [ $? -eq 0 ] then
Process3
if [ $? -eq 0 ] then
..
..
..
..
if [ $? -eq 0 ] then
Process10
else
exit

So here the script will exit anytime if any one of the process fails to complete with status 0. So again, if process5 fails, and user corrects the problem and restarts script, the script should start with process5 again and not process1 or at least there should be an option to user if he wants to resume the script or start it back from beginning i.e. process1.

What all possible ways we can code this kind of script, also please bear in mind, I am not allowed to use a temporary db, where I can store the status of each process.

I need to code in sh (shell script) in unix.

Upvotes: 3

Views: 327

Answers (1)

William Pursell
William Pursell

Reputation: 212434

A simple solution would be to write stamp files:

#/bin/sh

set -e  # Automatically abort if any simple command fails

if ! test -f cmd1-stamp; cmd1; fi
touch cmd1-stamp
if ! test -f cmd2-stamp; cmd2; fi
touch cmd2-stamp

When the script executes, if cmd1-stamp exists, cmd1 is not executed. Otherwise, cmd1 is executed. The script will abort if it fails. Note that it is very tempting to write test -f cmd1-stamp || cmd1, and this seems to work ( in bash ) but the shell specs state that the shell shall abort if the simple command that fails is not a part of an AND or OR list, and I suspect this is (yet another) instance of bash not conforming to the spec. (Although it doesn't seem to specify that the shell shall not abort if the failing command is part of an AND or OR list.)

Upvotes: 3

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