Greetings. This is my first post in this forum; I hope y'all find it useful. One caveat: "Concise" is my middle name. NOT!
I am almost done with a shell script that runs as a daemon. It monitors a message log that is frequently written to by a database server but it it works my client will have more such daemons.
After a few rough starts and things that just don't work, I am using dtksh (M-12/28/93d; the alternative on my client's old Solaris box was ksh 88). Here's how the loop works:
Code:
tail -0f $ONLINELOG |
while true # Loop until a break command
do
if [[ $go_flag -eq $FALSE ]]
then
break
fi
read newline
<.... Do my stuff, parsing $newline for a significant event ...>
done
Now how do I send this daemon a message to clean up after itself and exit quietly? Well, before I started that loop, I set up a simple, one-signal trap command:
Code:
trap 'echo Interrupt received; go_flag=$FALSE; break' INT
(I'm not even certain that break will do what I think.) All so very logical! So what's the problem?
Well, it is overwhelmingly likely that when I send it the "kill -2", my daemon will be sleeping on that "read newline" command. My output log shows that it did catch the signal but it goes right back to sleep on that read!
A Google search [ksh signal break read] showed me I am not alone; the first hit was a 5-year-old posting on this very forum. I was quite unhappy with the conclusion of that thread but even if ksh83v (the latest I've heard of) has fixed the issues discussed in that thread, I have no access to that. But I love to tinker so I added this to the trap handler:
Code:
trap 'echo Interrupt received; go_flag=$FALSE; echo "" >>$ONLINELOG; break' INT
What did I do up there?
I fed an extra empty line to the end of the file being tailed. (Remember, I'm not reading directly from the file but from a pipeline.) Hence, that read is immediately satisfied and the process awakens to see an empty line, continues back at the top of the loop, where it sees that $go_flag is $FALSE and breaks out of the loop.
This kluge worked for me, although it's a fair bet it won't work for everyone. And, of course, for all I know the SA_RESETHAND issue discussed in that post has been fixed.
Hi,
Could someone please tell me how to wakeup sleeping processes? (i.e. change the process status from "S" to "R" when viewing in ps command).
I ran a few programs in the background by "&" which went into "sleep" mode and I want them to run.
Any help will be greatly appreciated.
Steve (11 Replies)
Hi all,
Can anybody send the autosys developer sample resumes.
If this is not the correct place to ask please let me know where can I get them.
Your help would be appreciated.
Thanks
Renuka (0 Replies)
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Hi
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Dear shell experts,
I spent last few days porting ksh script from ksh88/SunOS to ksh93/Linux.
Basically, things are going well and I do not have too much troubles porting ks88 script to ksh93, but I stuck on one item. It's about sending and handling the signal.
I found two similar... (8 Replies)
Discussion started by: bzk
8 Replies
LEARN ABOUT SUNOS
continue
break(1) User Commands break(1)NAME
break, continue - shell built-in functions to escape from or advance within a controlling while, for, foreach, or until loop
SYNOPSIS
sh
break [n]
continue [n]
csh
break
continue
ksh
*break [n]
*continue [n]
DESCRIPTION
sh
The break utility exits from the enclosing for or while loop, if any. If n is specified, break n levels.
The continue utility resumes the next iteration of the enclosing for or while loop. If n is specified, resume at the n-th enclosing loop.
csh
The break utility resumes execution after the end of the nearest enclosing foreach or while loop. The remaining commands on the current
line are executed. This allows multilevel breaks to be written as a list of break commands, all on one line.
The continue utility continues execution of the next iteration of the nearest enclosing while or foreach loop.
ksh
The break utility exits from the enclosed for, while, until, or select loop, if any. If n is specified, then break n levels. If n is
greater than the number of enclosing loops, the outermost enclosing loop shall be exited.
The continue utility resumes the next iteration of the enclosed for, while, until, or select loop. If n is specified then resume at the n-
th enclosed loop. If n is greater than the number of enclosing loops, the outermost enclosing loop shall be used.
On this man page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:
1. Variable assignment lists preceding the command remain in effect when the command completes.
2. I/O redirections are processed after variable assignments.
3. Errors cause a script that contains them to abort.
4. Words that follow a command preceded by ** that are in the format of a variable assignment are expanded with the same rules as a vari-
able assignment. This means that tilde substitution is performed after the = sign, and also that word splitting and file name genera-
tion are not performed.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
SEE ALSO csh(1), exit(1), ksh(1), sh( 1), attributes(5)SunOS 5.10 17 Jul 2002 break(1)
07-14-2016
Signal trapped during read resumes sleeping
