SED help (remove line::parse again::add line) Post: 302142125

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Top Forums Shell Programming and Scripting SED help (remove line::parse again::add line) Post 302142125 by drl on Wednesday 24th of October 2007 12:36:25 PM

10-24-2007

Registered User

Quote:

Originally Posted by bakunin

The reason is: sed will read the first line of the input file (which is "file"), apply any rules that might be applicable and then write the result (the changed or not changed line) to <stdout>. This <stdout> is at this moment pointing to "file" and this is why after the first line the file will contain nothing more than exactly that first line - so sed encounters the EOF and thinks it is finished.

I would have explained this behaviour somewhat differently: when the shell begins to process a command line, it will literally remove the characters that involve re-direction. In dealing with re-direction, the shell will "zero" a file that is being re-directed to. If there was data on the file, it will have been erased before the command is executed. The result is that the command -- in this case sed -- will never see any input, because it already has been destroyed. The first read will encounter EOF.

Most of us have fallen into this operational trap. For example, we often want to sort a file onto itself -- just re-ordering data, neither gaining or losing data. So sort has an option to write the output to the input file, but one must use "-o file", and not "> file". The GNU sed allows a similar construction with "in-place" editing, but what actually happens is that sed writes to a temporary file and then renames it at the end. You can see this if you display the inode number (ls -li file) before and after the operation. You'll see that they are different.

The flow-chart of shell operations is displayed in some books, for example, O'Reilly's Learning the bash shell, 2nd, page 177 ff ... cheers, drl

drl

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ecaccess-event-grant

ECACCESS-EVENT-GRANT(1p)				User Contributed Perl Documentation				  ECACCESS-EVENT-GRANT(1p)

NAME

       ecaccess-event-grant - Grant usage of an ECaccess Event

SYNOPSIS

       ecaccess-event-grant -version|-help|-manual

       ecaccess-event-grant [-debug] [-subscribe] [-notify] event-id user-list

DESCRIPTION

       Allow managing the Event permissions for a list of user(s).

       The permissions can be either subscribe, notify, both or none. In order to remove permissions to an Event for a list of users use this
       command with no -subscribe and -notify options.

ARGUMENTS

       event-id
	       The identifier of the Event to grant.

       user-list
	       The user(s) to give/remove the permissions. Multiple users should be separated by a column (e.g. abc,def).

OPTIONS

       -subscribe
	       The user(s) specified in the user-list will be allowed to subscribe to the event-id (e.g. with the -eventIds option of the
	       ecaccess-job-submit command).

       -notify The user(s) specified in the user-list will be allowed to send notifications to the event-id (e.g. with the ecaccess-event-send
	       command).

       -version
	       Display version number and exits.

       -help   Print a brief help message and exits.

       -manual Prints the manual page and exits.

       -debug  Display the SOAP messages exchanged.

EXAMPLES

       ecaccess-event-grant -subscribe 167 abc,def,jhi

       Allow the users abc, def and jhi to subscribe to this Event.

       ecaccess-event-grant 167 jkl

       Remove all rights to the Event for the user jkl.

SEE ALSO

       ecaccess-event-clear, ecaccess-event-delete, ecaccess-event-send, ecaccess-event-list, ecaccess-event-create and ecaccess.

perl v5.14.2							    2012-04-16						  ECACCESS-EVENT-GRANT(1p)