Command Line Scheduling – Simple Way to Schedule a Single Future Event

command linescheduling

There are often times that I want my computer to do a single task, but not right now. For example, I could have it notify me in 30 minutes that it is time to leave work. Or maybe I want it to run a complicated test 2 hours from now when I'm sure most everyone else will be gone from the office.

I know I could create a cron job to run at a specific time of day, but that seems like a lot of work when all I want is something simple like "Run this script in 10 minutes", besides I'd have to figure out what time it will actually be X minutes/hours/days from now, and then delete the cron job once it finished.

Of course I could just write this script and run it in the background:

sleep X
do_task

But that just seems so clunky: I either need a new script for each task, or I need to write and maintain a script generic enough to do what I want, not to mention I have to figure out how many seconds are in the minutes, hours, or days I want.

Is there not an already established solution to this problem?

Best Answer

I use a simple script with at:

#!/bin/bash
# email reminder notes using at(1)...

read -p "Time of message? [HH:MM] " time
read -p "Date of message? [dd.mm.yy] " date
read -p "Message body? " message

at "$time" "$date" <<EOF
echo "$message" | mailx -s "REMINDER" me@gmail.com
EOF

You could just as easily pipe the $message to notify-send or dzen if you wanted a desktop notification instead of an email.

Related Solutions

Bash – Run program x minutes after finishing

cron sounds unsuitable for this; an hour after the completion of the previous run could either be done via a while loop

#!/bin/sh
while :; do
    some_job_that_takes_a_while
    sleep 3600
done

or by scheduling the next run in one hour via at(1) at the end of the job.

$ cat atat
#!/bin/sh
echo running the job
echo $HOME/atat | at now + 1 hours
$ ./atat
running the job
job 4 at 2015-09-30 17:00
$ date
Wed Sep 30 16:00:19 UTC 2015
$

There may need to be sanity checks or a timeout on the job, in the event it gets stuck and thus no subsequent jobs run until someone manually kills it and restarts things.

How to set (find) atime in seconds

Note that when you do -mtime <timespec>, the <timespec> checks the age of the file at the time find was started.

Unless you run it in a very small directory tree, find will take several milliseconds (if not seconds or hours) to crawl the directory tree and do a lstat() on every file. So having a precision of shorter than a second doesn't necessarily make a lot of sense.

Also note that not all file systems support time stamps with subsecond granularity.

Having said that, there are a few options.

With the find of many BSDs and the one from schily-tools, you can do:

find . -atime -1s

To find files that have been last accessed less than one second ago (compared to when find was started).

With zsh:

ls -ld -- **/*(Dms-1)

For subsecond granularity, with GNU tools, you can use a reference file whose atime you set with touch:

touch -ad '0.5 seconds ago' ../reference
find . -anewer ../reference

Or with recent versions of perl:

perl -MTime::HiRes=lstat,clock_gettime -MFile::Find -le '
  $start =  clock_gettime(CLOCK_REALTIME) - 0.5;
  find(
    sub {
      my @s = lstat $_;
      print $File::Find::name if @s and $s[8] > $start
    }, ".")'

Best Answer

Related Solutions

Bash – Run program x minutes after finishing

How to set (find) atime in seconds

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