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Full Discussion: code checking
Top Forums Shell Programming and Scripting code checking Post 302558201 by maverick72 on Friday 23rd of September 2011 05:05:18 AM
Old 09-23-2011
Code:
# prgname='test.sh' # cat $prgname sleep 120 # sh test.sh  &                    [1]     25806

That part is telling ya to assign the script name to the variable prgname, what it does (the cat part) and he's executing it in background (&). You can see the process id of the script at the end (25806).

He's just showing you that the script is already running so you can test it.

Code:
# if [ "$(ps -ef|awk '/'${prgname}'/ && !/awk/')." != "." ] > then > echo "${prgname} running !" > fi test.sh running !

That part is the actual loop thats looking for the running script. [ ] Tests if the script is already running. If it does it echo's "(script name) running!". The last part is the actualy the result of the command which tells you ... yeah your script is running.

Back a bit... the test part.

[ ] this is the test part. So if [test] is true do something.

Test what? If the variable exist. If it exists you want to know.

ps -ef will list the processes (good thing to know if your looking for a process).

He's pipping it into a awk which will search for the variable prgname BUT will leave out awk. You always want to do this cause else it will always return with your actual search. See ex:

Code:
$ ps -ef | awk '/'ssh-agent'/'
user     1625 25793  0 10:55 pts/2    00:00:00 awk /ssh-agent/
user    20491     1  0 Sep19 ?        00:00:00 ssh-agent

You want the second one but not the first one. So the AND operator (&&) is really needed here to skip your search.

Ok ... last thing he does ... he assigns the result to a variable PLUS a dot "$(bla bla bla bla)."

See the trailling dot at the end? Thats actually needed incase your result is empty. If it is your variable will be a simple dot. That simple dot will be compared the other part of the test "."

That != says NOT equal so if it finds your script name that test will look like:

test.sh. (see the dot at the end of test.sh) NOT equal to dot

That test is true so do somehing.

In case its not running the test will look like this:

"." NOT equal to "." which is not true so it will skip the "do something part"

Hope it helped. Thats really the simplest i can do.
 

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LEARN ABOUT OPENSOLARIS

halockrun

halockrun(1M)						  System Administration Commands					     halockrun(1M)

NAME

       halockrun - run a child program while holding a file lock

SYNOPSIS

       /usr/cluster/bin/halockrun [-nsv] [-e exitcode] lockfilename
       prog [args]

DESCRIPTION

       The halockrun utility provides a convenient means to claim a file lock on a file and run a program while holding that lock. As this utility
       supports script locking, this utility is useful when programming in scripting languages such as the Bourne shell. See sh(1).

       halockrun opens the file lockfilename and claims an exclusive mode file lock on the entire file. See fcntl(2) fcntl(2)). Then it  runs  the
       program	prog  with arguments args as a child process and waits for the child process to exit. When the child exits, halockrun releases the
       lock, and exits with the same exit code with which the child exited.

       The overall effect is that the child prog is run as a critical section, and that this critical section is well-formed, in  that	no  matter
       how the child terminates, the lock is released.

       If the file lockfilename cannot be opened or created, then halockrun prints an error message on stderr and exits with exit code 99.

       You  can  run  this command in the global zone or in a non-global zone. The command affects only the global or non-global zone in which you
       issue the command.

OPTIONS

       The following options are supported:

       -e exitcode		   Normally, errors detected by halockrun exit with exit code 99. The -e option provides a means  to  change  this
				   special exit code to a different value.

       -n			   The	lock  should be requested in non-blocking mode: if the lock cannot be granted immediately, halockrun exits
				   immediately, with exit code 1, without running prog. This behavior is not affected by the -e option.

				   Without the -n option, the lock is requested in blocking mode, thus, the halockrun utility blocks  waiting  for
				   the lock to become available.

       -s			   Claim the file lock in shared mode, rather than in exclusive mode.

       -v			   Verbose output, on stderr.

EXIT STATUS

       Errors  detected  by halockrun itself, such that the child process was never started, cause halockrun to exit with exit code 99. (This exit
       code value can be changed to a different value using the -e option. See OPTIONS.

       Otherwise, halockrun exits with the same exit code with which the child exited.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWscu			   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Evolving			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       fcntl(2), attributes(5)

Sun Cluster 3.2 						    10 Apr 2006 						     halockrun(1M)
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