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Top Forums Shell Programming and Scripting Script that will look the same as Cron Post 303037672 by drysdalk on Friday 9th of August 2019 09:29:08 AM
Old 08-09-2019
Hi,

If you definitely don't have access to the crontab for the user you want to run the script as, and if you can't get the person who has root on the box in question to set it up for you, then one approach would be to have a script that runs in an infinite loop until a target time arrives, and then runs whatever task it's meant to run at that time.

Here's an example of such a script, showing the code and me starting to run it roughly ten seconds before the appointed time:

Code:
$ cat script.sh 
#!/bin/bash

runtime=`/usr/bin/date -d '2019-08-09 14:22:00' +%s`

while true
do
        nowtime=`/usr/bin/date +%s`

        if [ "$runtime" == "$nowtime" ]
        then
                date
                echo "It's time to run"
                exit 0
        else
                date
                echo "It's not time to run, I'll keep waiting"
        fi

        /usr/bin/sleep 1
done

$ ./script.sh 
Fri Aug  9 14:21:50 BST 2019
It's not time to run, I'll keep waiting
Fri Aug  9 14:21:51 BST 2019
It's not time to run, I'll keep waiting
Fri Aug  9 14:21:52 BST 2019
It's not time to run, I'll keep waiting
Fri Aug  9 14:21:53 BST 2019
It's not time to run, I'll keep waiting
Fri Aug  9 14:21:54 BST 2019
It's not time to run, I'll keep waiting
Fri Aug  9 14:21:55 BST 2019
It's not time to run, I'll keep waiting
Fri Aug  9 14:21:56 BST 2019
It's not time to run, I'll keep waiting
Fri Aug  9 14:21:57 BST 2019
It's not time to run, I'll keep waiting
Fri Aug  9 14:21:58 BST 2019
It's not time to run, I'll keep waiting
Fri Aug  9 14:21:59 BST 2019
It's not time to run, I'll keep waiting
Fri Aug  9 14:22:00 BST 2019
It's time to run
$

So the basic idea is we define our target time in the runtime variable at the top, converting a human-readable date into the UNIX epoch (the number of seconds since the start of 1970). We then in an infinite loop check the current time, compare it to our target time, and do something specific if the two match. If the current time is not the target time, we wait one second, and the loop goes round again until the target time arrives.

Note that this isn't entirely ideal, and you'd need to run this via screen or tmux or something similar to ensure that the script didn't die when your terminal session did. But if you really definitely don't have access to an actual system-level task scheduler, this kind of approach will work in a pinch. You might also want to make the sleep command wait for less than one second, just to be sure you don't ever miss the target second you want your job to actually run, but that's the only other issue that immediately comes to mind.

Hope this helps !
 

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RunTargetUnitTests(1)					    BSD General Commands Manual 				     RunTargetUnitTests(1)

NAME
RunTargetUnitTests -- run unit tests for the current target SYNOPSIS
RunTargetUnitTests DESCRIPTION
RunTargetUnitTests examines its environment and runs the unit tests it presumes are present using otest(1). RunTargetUnitTests is intended to be called from a shell script build phase. It expects certain environment variables to be configured from Xcode build settings (see below). RunTargetUnitTests will run tests for all built architectures appropriate for the machine running the tests. ENVIRONMENT
ARCHS The architectures the tests were built for; when tests are run, they will be run once per architecture. If unspecified, tests are run for the architecture returned by arch(1). DEVELOPER_DIR The Xcode folder, e.g. "/Developer". If unspecified the value for SYSTEM_DEVELOPER_DIR will be used, or "/Developer" if that also is unspecified. BUILT_PRODUCTS_DIR The directory containing built products; when tests are run, this is specified in DYLD_FRAMEWORK_PATH. If unspecified tests are run from the current working directory with no DYLD_FRAMEWORK_PATH. FULL_PRODUCT_NAME The full name of the built product, including its wrapper extension if any. GCC_ENABLE_OBJC_GC Whether or not the test bundle was compiled with Objective-C garbage collection enabled. Possible values are unsupported, supported, and required. If not set, defaults to unsupported, which will run otest(1) with Objective-C garbage collection disabled. NATIVE_ARCH_ACTUAL The architecture of the machine running the tests, used to determine for which architectures tests can be run. If unspecified, defaults to the architecture returned by arch(1). OTEST The path to the otest command line tool; defaults to /Developer/Tools/otest. TEST_AFTER_BUILD Set to YES to run tests, any other value will prevent test execution. FILES
/Developer/Tools/RunTargetUnitTests The script used to run tests from a shell script build phase. /Developer/Tools/otest The OCUnit test rig. SEE ALSO
arch(1), otest(1) Mac OS X June 2, 2019 Mac OS X
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