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Top Forums UNIX for Advanced & Expert Users Redirect contained in variable not expanded as expected Post 302367769 by noose on Tuesday 3rd of November 2009 11:37:21 AM
Old 11-03-2009
Question Redirect contained in variable not expanded as expected

Hi all,

I have a selection of files that contain several commands that write to a file and are started as background processes similar to below.
Code:
command_to_run_simulator -simulator_arguments > log_file 2>&1 &
command_to_run_simulator -simulator_arguments > log_file 2>&1 &
command_to_run_simulator -simulator_arguments > log_file 2>&1 &

I want to write a wrapper script that will read each file a line at a time, execute that line and store the PID for each line so that after a certain amount of time the processes can be killed.

I haven't implemented a full script for this but what I have written is here:
Code:
#!/bin/sh

while read line
do
 $line
  # command_to_run_simulator -simulator_arguments > log_file 2>&1 &
  echo $!
done < $1

I was expecting that each line in the file would be read output and run. If I insert the commented line, an exact copy from the original file, it works fineSmilie. If I leave the variable in there then I get the following errorSmilie:
Unexpected option '>'

It seems that when $line is expanded somehow the meaning of the redirection symbol is lost. Can anyone explain how $line is expanded and why the redirection is lost? As a secondary thing, is there a better way to achieve what I'm trying to do?

Please ask if anything isn't clear or I've missed relevant information. On that note, my shell is GNU bash, version 3.00.15(1)-release (x86_64-redhat-linux-gnu).

Many thanks,
Geoff.
 

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set(1F) 							   FMLI Commands							   set(1F)

NAME
set, unset - set and unset local or global environment variables SYNOPSIS
set [-l variable [=value]] ... set [-e variable [=value]] ... set [-ffile variable [=value]]... ... unset -l variable... unset -f file variable... DESCRIPTION
The set command sets variable in the environment, or adds variable=value to file. If variable is not equated it to a value, set expects the value to be on stdin. The unset command removes variable. Note that the FMLI predefined, read-only variables (such as ARG1), may not be set or unset. Note that at least one of the above options must be used for each variable being set or unset. If you set a variable with the -ffilename option, you must thereafter include filename in references to that variable. For example, ${(file)VARIABLE}. FMLI inherits the UNIX environment when invoked. OPTIONS
-l Sets or unsets the specified variable in the local environment. Variables set with -l will not be inherited by processes invoked from FMLI. -e Sets the specified variable in the UNIX environment. Variables set with -e will be inherited by any processes started from FMLI. Note that these variables cannot be unset. -ffile Sets or unsets the specified variable in the global environment. The argument file is the name, or pathname, of a file containing lines of the form variable=value. file will be created if it does not already exist. Note that no space intervenes between -f and file. EXAMPLES
Example 1 A sample output of set command. Storing a selection made in a menu: name=Selection 2 action=`set -l SELECTION=2`close NOTES
Variables set to be available to the UNIX environment (those set using the -e option) can only be set for the current fmli process and the processes it calls. When using the -f option, unless file is unique to the process, other users of FMLI on the same machine will be able to expand these vari- ables, depending on the read/write permissions on file. A variable set in one frame may be referenced or unset in any other frame. This includes local variables. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
env(1), sh(1), attributes(5) SunOS 5.11 5 Jul 1990 set(1F)
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