How to Force command substitution evaluation in bash? Post: 302969885

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Top Forums Shell Programming and Scripting How to Force command substitution evaluation in bash? Post 302969885 by Don Cragun on Tuesday 29th of March 2016 02:50:04 PM

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03-29-2016

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Quote:

Originally Posted by siegfried

Yes! As I you inferred: $(BackupRecords --log) very similar to $(date +'%Y %b %d %H:%M:%ss'). If I call it too often, I get different log files (which is usually what I want).

However, in this case, I want the same log file for multiple uses within the same script. How can I evaluate $(BackupRecords --log) only once at the beginning of my script once and use it multiple times later in the script?

Thanks
Siegfried

You're missing the point. The code you have does call BackupRecords --log once at the start of your script and uses the string returned by that call throughout the rest of your script. Therefore, the string returned by that command must contain something that is re-evaluating the date every time $BUPLOG is evaluated.

If you won't show us the code for BackupRecords, it is REALLY REALLY hard for us to tell you how to fix it to do what you want.

Don Cragun

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openvt

OPENVT(1)							     Linux 1.x								 OPENVT(1)

NAME

       openvt - start a program on a new virtual terminal (VT).

SYNOPSIS

       openvt [-c vtnumber] [OPTIONS] [--] command

DESCRIPTION

       openvt  will  find the first available VT, and run on it the given command with the given command options, standard input, output and error
       are directed to that terminal. The current search path ($PATH) is used to find the requested command. If no command is specified  then  the
       environment variable $SHELL is used.

   OPTIONS
       -c, --console=VTNUMBER
	      Use the given VT number and not the first available. Note you must have write access to the supplied VT for this to work;

       -f, --force
	      Force opening a VT without checking whether it is already in use;

       -e, --exec
	      Directly execute the given command, without forking.  This option is meant for use in /etc/inittab;

       -s, --switch
	      Switch to the new VT when starting the command. The VT of the new command will be made the new current VT;

       -u, --user
	      Figure out the owner of the current VT, and run login as that user.  Suitable to be called by init. Shouldn't be used with -c or -l;

       -l, --login
	      Make the command a login shell. A - is prepended to the name of the command to be executed;

       -v, --verbose
	      Be a bit more verbose;

       -w, --wait
	      wait  for command to complete. If -w and -s are used together then openvt will switch back to the controlling terminal when the com-
	      mand completes;

       -V, --version
	      print program version and exit;

       -h, --help
	      show this text and exit.

       --     end of options to openvt.

NOTE

       If openvt is compiled with a getopt_long() and you wish to set options to the command to be run, then you must supply the end of options --
       flag before the command.

EXAMPLES

       openvt can be used to start a shell on the next free VT, by using the command:

       openvt bash

       To start the shell as a login shell, use:

       openvt -l bash

       To get a long listing you must supply the -- separator:

       openvt -- ls -l

HISTORY

       Earlier, openvt was called open.  It was written by Jon Tombs <jon@gtex02.us.es or jon@robots.ox.ac.uk>.  The -w idea is from "sam".

SEE ALSO

       chvt(1), doshell(8), login(1)

19 Jul 1996							       V1.4								 OPENVT(1)