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Full Discussion: Is this the "right" way to make an alarmclock?
Top Forums Shell Programming and Scripting Is this the "right" way to make an alarmclock? Post 302557922 by alister on Thursday 22nd of September 2011 11:09:51 AM
Old 09-22-2011
Quote:
Originally Posted by ninjaaron
Code:
#!/bin/bash

time="$1"
command="$2"
trig=0

while [ $trig = 0 ]; do
	if [ "$(date +%R)" = $time ]; then
		$command
		trig=1
	else
		sleep 5
		
	fi
done
exit

In my opinion, your simple script is too complex. Smilie

Why not directly use the date-$time check as the loop condition? This way, $trig is not needed. Also, it may be more useful to have this script return the exit status of $command.

For your consideration:
Code:
#!/bin/sh

time="$1"
command="$2"

while [ "$(date +%H:%M)" != "$time" ]; do
	sleep 5
done
$command

Also, for portability, I made some minor modifications that may not be of any interest to you.

Since there's nothing bash-specific about this little script, I changed /bin/bash to /bin/sh. Should you ever need to run it on a system that does not have bash, it will still work.

A system without bash may have a date command that does not support the %R format. Since that's equivalent to the standard %H:%M, I used that instead.

Regards,
Alister
Last edited by alister; 09-22-2011 at 12:17 PM..
This User Gave Thanks to alister For This Post:
ninjaaron
 

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LEARN ABOUT CENTOS

lksh

LKSH(1) 						    BSD General Commands Manual 						   LKSH(1)

NAME

     lksh -- Legacy Korn shell built on mksh

SYNOPSIS

     lksh [-+abCefhiklmnprUuvXx] [-+o opt] [-c string | -s | file [args ...]]

DESCRIPTION

     lksh is a command interpreter intended exclusively for running legacy shell scripts.  It is built on mksh; refer to its manual page for
     details on the scripting language.  It is recommended to port scripts to mksh instead of relying on legacy or idiotic POSIX-mandated behav-
     iour, since the MirBSD Korn Shell scripting language is much more consistent.

LEGACY MODE

     lksh has the following differences from mksh:

     o	 lksh is not suitable for use as /bin/sh.

     o	 There is no explicit support for interactive use, nor any command line editing or history code.  Hence, lksh is not suitable as a user's
	 login shell, either; use mksh instead.

     o	 The KSH_VERSION string identifies lksh as ``LEGACY KSH'' instead of ``MIRBSD KSH''.

     o	 lksh only offers the traditional ten file descriptors to scripts.

     o	 lksh uses POSIX arithmetics, which has quite a few implications: The data type for arithmetics is the host ISO C long data type.  Signed
	 integer wraparound is Undefined Behaviour.  The sign of the result of a modulo operation with at least one negative operand is unspeci-
	 fied.	Shift operations on negative numbers are unspecified.  Division of the largest negative number by -1 is Undefined Behaviour.  The
	 compiler is permitted to delete all data and crash the system if Undefined Behaviour occurs.

     o	 The rotation arithmetic operators are not available.

     o	 The shift arithmetic operators take all bits of the second operand into account; if they exceed permitted precision, the result is
	 unspecified.

     o	 The GNU bash extension &> to redirect stdout and stderr in one go is not parsed.

     o	 The mksh command line option -T is not available.

     o	 Unless set -o posix is active, lksh always uses traditional mode for constructs like:

	       $ set -- $(getopt ab:c "$@")
	       $ echo $?

	 POSIX mandates this to show 0, but traditional mode passes through the errorlevel from the getopt(1) command.

     o	 lksh, unlike AT&T UNIX ksh, does not keep file descriptors > 2 private.

SEE ALSO

     mksh(1)

     https://www.mirbsd.org/mksh.htm

     https://www.mirbsd.org/ksh-chan.htm

CAVEATS

     lksh tries to make a cross between a legacy bourne/posix compatibl-ish shell and a legacy pdksh-alike but ``legacy'' is not exactly speci-
     fied.

     The set built-in command does not have all options one would expect from a full-blown mksh or pdksh.

     Talk to the MirOS development team using the mailing list at <miros-mksh@mirbsd.org> or the #!/bin/mksh (or #ksh) IRC channel at
     irc.freenode.net (Port 6697 SSL, 6667 unencrypted) if you need any further quirks or assistance, and consider migrating your legacy scripts
     to work with mksh instead of requiring lksh.

MirBSD								    May 2, 2013 							    MirBSD
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