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Full Discussion: Dynamically setting of environment variable... Can it be done?
Top Forums Shell Programming and Scripting Dynamically setting of environment variable... Can it be done? Post 302555443 by Corona688 on Wednesday 14th of September 2011 06:22:09 PM
Old 09-14-2011
If you have a new enough ksh, you can do things like this:

Code:
$ NAME="VAR"
$ VAR="1234"
echo "${!NAME}"
1234
$

If you don't, it's going to be ugly:

Code:
$ data_file_123=sales.dat
$ PARAM="123"
$ VARSTR="\${data_file_${PARAM}}"
$ echo "${VARSTR}"
${data_file_123}
$ eval echo "$VARSTR"
sales.dat

Beware, eval carries a hidden danger:

Code:
$ PARAM="} ; touch / ; \${1"
$ VARSTR="\${data_file_${PARAM}}"
$ echo "${VARSTR}"
${data_file_} ; touch / ; ${1}
$ eval echo ${VARSTR}

touch: setting times of `/': Permission denied
$

This User Gave Thanks to Corona688 For This Post:
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LEARN ABOUT DEBIAN

rabbitmq-env.conf

RABBITMQ-ENV.CONF(5)						  RabbitMQ Server					      RABBITMQ-ENV.CONF(5)

NAME

       rabbitmq-env.conf - default settings for RabbitMQ AMQP server

DESCRIPTION

       /etc/rabbitmq/rabbitmq-env.conf contains variable settings that override the defaults built in to the RabbitMQ startup scripts.

       The file is interpreted by the system shell, and so should consist of a sequence of shell environment variable definitions. Normal shell
       syntax is permitted (since the file is sourced using the shell "." operator), including line comments starting with "#".

       In order of preference, the startup scripts get their values from the environment, from /etc/rabbitmq/rabbitmq-env.conf and finally from
       the built-in default values. For example, for the RABBITMQ_NODENAME setting,

       RABBITMQ_NODENAME

       from the environment is checked first. If it is absent or equal to the empty string, then

       NODENAME

       from /etc/rabbitmq/rabbitmq-env.conf is checked. If it is also absent or set equal to the empty string then the default value from the
       startup script is used.

       The variable names in /etc/rabbitmq/rabbitmq-env.conf are always equal to the environment variable names, with the RABBITMQ_ prefix
       removed: RABBITMQ_NODE_PORT from the environment becomes NODE_PORT in the /etc/rabbitmq/rabbitmq-env.conf file, etc.

       # I am a complete /etc/rabbitmq/rabbitmq-env.conf file.
       # Comment lines start with a hash character.
       # This is a /bin/sh script file - use ordinary envt var syntax
       NODENAME=hare

SEE ALSO

       rabbitmq-server(1) rabbitmqctl(1)

EXAMPLES

       # I am a complete /etc/rabbitmq/rabbitmq-env.conf file.
       # Comment lines start with a hash character.
       # This is a /bin/sh script file - use ordinary envt var syntax
       NODENAME=hare

       This is an example of a complete /etc/rabbitmq/rabbitmq-env.conf file that overrides the default Erlang node name from "rabbit" to "hare".

AUTHOR

       The RabbitMQ Team <info@rabbitmq.com>

RabbitMQ Server 						    06/22/2012						      RABBITMQ-ENV.CONF(5)
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