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Full Discussion: Explanation for interesting sed behaviour?
Top Forums Shell Programming and Scripting Explanation for interesting sed behaviour? Post 302355944 by Gavster on Thursday 24th of September 2009 07:07:51 AM
Old 09-24-2009
Thanks guys for the quick replies.

In response to pludi's explanation, I have been going through a mental experiment with pencil and paper to figure out the sequence of events with this line of code:
cat $file | sed 's/phrase/substitute/' > $file
I can understand how this might result in truncated files (which I have also seen). Essentially, if the redirection begins writing back to the file before the cat command had finished buffering it, I can see how we could loose the end of the file.

But that still doesn't explain (in my mind at least) how I could end up with a file of zero bytes in size. Surely, for this to happen, the redirection would have written (opened) the file before cat had even started reading it?!?! Is this possible?

Unfortunately, my knowledge of process scheduling and file IO in Linux is extremely limited so I'm not entirely sure.

Gavin
 

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LEARN ABOUT DEBIAN

ocf_heartbeat_stateful

OCF_HEARTBEAT_STATEF(7) 					OCF resource agents					   OCF_HEARTBEAT_STATEF(7)

NAME

       ocf_heartbeat_Stateful - Example stateful resource agent

SYNOPSIS

       Stateful [start | stop | monitor | meta-data | validate-all]

DESCRIPTION

       This is an example resource agent that impliments two states

SUPPORTED PARAMETERS

       state
	   Location to store the resource state in (unique, optional, string, default
	   /var/run/resource-agents/Stateful-{OCF_RESOURCE_INSTANCE}.state)

SUPPORTED ACTIONS

       This resource agent supports the following actions (operations):

       start
	   Starts the resource. Suggested minimum timeout: 20s.

       stop
	   Stops the resource. Suggested minimum timeout: 20s.

       monitor
	   Performs a detailed status check. Suggested minimum timeout: 20. Suggested interval: 10.

       meta-data
	   Retrieves resource agent metadata (internal use only). Suggested minimum timeout: 5.

       validate-all
	   Performs a validation of the resource configuration. Suggested minimum timeout: 20s.

EXAMPLE

       The following is an example configuration for a Stateful resource using the crm(8) shell:

	   primitive p_Stateful ocf:heartbeat:Stateful 
	     op monitor depth="0" timeout="20" interval="10"

SEE ALSO

       http://www.linux-ha.org/wiki/Stateful_(resource_agent)

AUTHOR

       Linux-HA contributors (see the resource agent source for information about individual authors)

resource-agents UNKNOWN 					    03/09/2014						   OCF_HEARTBEAT_STATEF(7)
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