Shell script: fire a command if system time is equal to given time

Question

I am very new to shell scripting. The script should fire a command if the given time as command line argument is equal to the system time, else it should wait(poll) for the given time.

I started with very basics, but i am stuck here only:-(

#!/bin/sh

now=$(date +%k%M)
cur="055" # should be given as command line arg
if ($now == $cur)
then
    echo "Fire command here"
else
    echo "poll for time"
fi

When i execute the script:

./script.sh: line 5: 055: command not found

poll for time

Thanks for the help.

Do you know [`cron`](http://en.wikipedia.org/wiki/cron) can trigger command at given time — Édouard Lopez, Sep 02 '13 at 14:00
Check here [How to read date from terminal and compare with current date](http://stackoverflow.com/q/14501734/802365). — Édouard Lopez, Sep 02 '13 at 14:03
yep, I was talking about cron jobs, just as another POV on your problem — Édouard Lopez, Sep 02 '13 at 14:03
@James Should you be specific on the very second, minute or hour? You could also use `crontab` or `at`, but to make life easier you could also wrap them with a script. — konsolebox, Sep 02 '13 at 14:50

Juto · Answer 1 · 2013-09-02T16:03:09.717

3

I think the above is just a small syntax error, instead of:

if ($now == $cur)

You may want to do this:

if [ $now -eq $cur ]  #very basic comparison here, you may want to have a
                      #look at the bash comparisons

Update Could you change the variable to,

$cur=$(date +%H%M)

And in case the input is not provided by you, you should remove the space in front of the $now

now=$(echo $now | sed 's/\s//g') #this removes the spaces in the input

edited Sep 02 '13 at 16:03

answered Sep 02 '13 at 14:07

Juto

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if i use `if [ $now -eq $cur ]` , i get `./script.sh: line 5: [: missing `]'` `poll for time` , i don't know why? – james Sep 02 '13 at 14:10
Did you put a space between the `[` and the `$now`? – Juto Sep 02 '13 at 14:12
I used the syntax suggested by you, it reflects the error:`./script.sh: line 5: [: missing `]'` – james Sep 02 '13 at 14:14
I mean, are you going to get from the command line the values padded by `\s` if the hour value is less than 10? – Juto Sep 02 '13 at 14:17

score 0 · Answer 2 · answered Sep 02 '13 at 14:14

0

You can run a program @ a particular time with :

crontab -e

and

0 14 * * * command

to run command @ 14 PM (by example)

answered Sep 02 '13 at 14:14

Gilles Quénot

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score 0 · Answer 3 · answered Sep 02 '13 at 14:21

0

begin="`date '+%s'`"
final=... #should be converted to seconds since epoch...
sleep $((final - begin))
exec_your_command

answered Sep 02 '13 at 14:21

MasterID

1,510
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Thanks, it does the job but calculating seconds since epoch is not user friendly. :-( – james Sep 02 '13 at 14:41

score 0 · Answer 4 · answered Sep 02 '13 at 15:25

The problem you described seems to be exactly what crontab is designed to handle, from wikipedia "Cron is driven by a crontab (cron table) file, a configuration file that specifies shell commands to run periodically on a given schedule."

Here is a quick reference, it is reletively barebones, but should be enough to determine if it meets your needs.

score 0 · Answer 5 · answered Oct 14 '14 at 06:58

0

Use following code

if [ $now == $cur ]

answered Oct 14 '14 at 06:58

Siddeshwar Vanga

20
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Shell script: fire a command if system time is equal to given time

5 Answers5