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Full Discussion: [Shell/Perl(?)] Prepending timestamps to console output & writing results to a file
Top Forums Shell Programming and Scripting [Shell/Perl(?)] Prepending timestamps to console output & writing results to a file Post 302647045 by agama on Sunday 27th of May 2012 12:23:31 AM
Old 05-27-2012
Quote:
Originally Posted by Vryali

That said, your fix works, thanks so much! Would you mind explaining a tiny snippet?

Code:
 ...; c | getline; close( c ); ...

Is that just prepending c to $0, basically, and if so, why does it need a close, I don't see an open?

Thanks!
Glad it worked. The line you asked about can be confusing.

The variable 'c' is assigned a command and as a result the construct c | getline basically causes awk to execute a popen() call (pipe open) which executes the command in a child process and pipes the results from that command back to awk. The first line of the output from the command is read by the getline, and since no variable is defined, it is parsed into the standard $0, $1... parameters. If a second getline is used with the same command it would attempt to read the next line of input from the command. This would result in and end of file as the date command returns only one line. So, the command must be closed in order for the next to be successful.

Behind the scenes awk maps the command to the file descriptor, so to close the descriptor the command string must be given to the close() function. This is easiest by assigning the command to a variable.

Hope this makes sense.

---------- Post updated at 00:23 ---------- Previous update was at 00:14 ----------

Found a bit more of a description that might do a better job than the paragraph I posted:

Close Files And Pipes - The GNU Awk User's Guide
Last edited by agama; 05-27-2012 at 01:25 AM.. Reason: correction.
This User Gave Thanks to agama For This Post:
Vryali
 

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LEARN ABOUT HPUX

tsm.lpadmin

tsm.lpadmin(1M) 														   tsm.lpadmin(1M)

NAME

       tsm.lpadmin - add or remove a printer for use with tsm(1)

SYNOPSIS

       printer model

       printer

DESCRIPTION

       is  used  to add (or remove) a printer to the LP spooling system when the printer is connected to the system through a terminal running the
       Terminal Session Manager (see tsm(1)).  is a shell script that uses in the normal way but also creates a named pipe to which LP	output	is
       directed (see lpadmin(1)).  This named pipe is opened by TSM and data flowing from it is sent to the printer through the terminal.

   Options
       recognizes the following options:

	      Names a printer to be created with an associated pipe.
			     If is used, must also be specified.

	      Selects a model interface program for
			     printer.	model is one of the model interface names supplied with the LP software (see the Models topic in the lpad-
			     min(1)) manual entry.  If is used, must also be specified.

	      Removes	     printer from the LP system.  No other options are allowed with

   Restrictions
       To use you must be user or

AUTHOR

       was developed by HP.

FILES

SEE ALSO

       lpadmin(1M), tsm(1).

																   tsm.lpadmin(1M)
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