File name with yyyymmddhhmi Post: 303019989

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Top Forums UNIX for Beginners Questions & Answers File name with yyyymmddhhmi Post 303019989 by rbatte1 on Wednesday 11th of July 2018 01:30:25 PM

07-11-2018

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You also need to ensure that your file creation and all the output being put into it is Atomic, i.e. a single operation that takes a single IO. Often this is done by creating the file and building it up with content as another name and then when it is ready, renaming it to it appears as a complete file instantly.

If you have a file that takes even a whole second to build, then you may sometimes be unlucky and fetch a partial file.

Something like this would illustrate it:-

Code:

((random_delay=$RANDOM%9))

( sleep $random_delay ; cat /tmp/myfile ) &      # Display the file at some undetermined time

date                             > /tmp/myfile
echo "First data line of file"  >> /tmp/myfile
sleep 3
echo "Second data line of file" >> /tmp/myfile
sleep 3
echo "Last data line of file"   >> /tmp/myfile
wait                                             # In case the random delay is long, wait for the background sleep/cat to finish

If you run this repeatedly, you may get 1, 2 or 3 lines of output. You can compensate by the cat reading a file that is always the finished article, so more like:-

Code:

((random_delay=$RANDOM%9))

( sleep $random_delay ; cat /tmp/finalfile ) &   # Display the file at some undetermined time

date                             > /tmp/myfile
echo "First data line of file"  >> /tmp/myfile
sleep 3
echo "Second data line of file" >> /tmp/myfile
sleep 3
echo "Last data line of file"   >> /tmp/myfile

mv /tmp/myfile /tmp/finalfile                    # Atomic file write
wait                                             # In case the random delay is long, wait for the background sleep/cat to finish

It may fail first time if the file does not exist, but afterwards it would only ever read a completed file.

Doing this, you could also make a link as a "latest" file, so you always know which one to pick up.

I hope that this helps,
Robin

rbatte1

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LEARN ABOUT OPENSOLARIS

rmvb

rmvb(9F)						   Kernel Functions for Drivers 						  rmvb(9F)

NAME

       rmvb - remove a message block from a message

SYNOPSIS

       #include <sys/stream.h>

       mblk_t *rmvb(mblk_t *mp, mblk_t *bp);

INTERFACE LEVEL

       Architecture independent level 1 (DDI/DKI).

PARAMETERS

       mp    Message from which a block is to be removed. mblk_t is an instance of the msgb(9S) structure.

       bp    Message block to be removed.

DESCRIPTION

       The  rmvb()  function  removes a message block (bp) from a message (mp), and returns a pointer to the altered message. The message block is
       not freed, merely removed from the message. It is the module or driver's responsibility to free the message block.

RETURN VALUES

       If successful, a pointer to the message (minus the removed block) is returned. The pointer is NULL if bp was the only block of the  message
       before  rmvb() was called. If the designated message block (bp) does not exist, -1 is returned.

CONTEXT

       The rmvb() function can be called from user, interrupt, or kernel context.

EXAMPLES

       This  routine  removes  all  zero-length M_DATA message blocks from the given message. For each message block in the message, save the next
       message block (line 10). If the current message block is of type M_DATA and has no data in its buffer (line 11), then remove  it  from  the
       message (line 12) and free it (line 13). In either case, continue with the next message block in the message (line 16).

	 1  void
	  2  xxclean(mp)
	  3	 mblk_t *mp;
	  4  {
	  5	     mblk_t *tmp;
	  6	     mblk_t *nmp;
	  7
	  8	     tmp = mp;
	  9	     while (tmp) {
	 10		      nmp = tmp->b_cont;
	 11		      if ((tmp->b_datap->db_type == M_DATA) &&
				    (tmp->b_rptr == tmp->b_wptr)) {
	 12			   (void) rmvb(mp, tmp);
	 13			   freeb(tmp);
	 14		      }
	 15		      tmp = nmp;
	 16	     }
	 17  }

SEE ALSO

       freeb(9F), msgb(9S)

       Writing Device Drivers

       STREAMS Programming Guide

SunOS 5.11							    16 Jan 2006 							  rmvb(9F)