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Full Discussion: How to check whether a variable is empty or contains some value?
Top Forums Shell Programming and Scripting How to check whether a variable is empty or contains some value? Post 302828273 by Little on Tuesday 2nd of July 2013 06:59:25 AM
Old 07-02-2013
How to check whether a variable is empty or contains some value?
hi,

i want to check whether a a variable contains some value or is empty in a shell script. so if the variable contains some value i want to do some job and if the variable doesnt contain any value then i need to skip that job.

here is a sample script

read_filenames.sh contains

Code:
FILENAME=$1

FILE="s1.txt"

if [ -n $FILENAME ]; then

      FILE=$FILENAME

fi

echo "FILE = {$FILE}"


so, when i run the script without passing any argument, variable "FILE" should contain "s1.txt". so the output should be

Code:
$ sh read_filenames.sh

FILE = {s1.txt}

but when i pass an argument to the script, then the variable "FILE" should contain the argument value. so the output should be

Code:
$ sh read_filenames.sh p1.txt

FILE = {p1.txt}

currently i am using the above code, but if i dnt pass any argument to the script. the output is

Code:
FILE = {}

i read somewhere that

Code:
if [ -n $FILENAME ]; then

checks whether the variable is empty or not. but i dnt think that its doing that job. can anyone tell how can i do the above.
 

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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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