Any real differences between "value" or 'value' or value


 
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# 1  
Any real differences between "value" or 'value' or value

I'm curious if there is any real difference between using " " or ' ' or no quotes at all. For example, I have a variable called EXTRACT_FILES. When I declare it, I set it to false... EXTRACT_FILES=false. I eventually use the variable later in the script (having set it to EXTRACT_FILES=true due to some condition being met) if I call this variable later to decide whether to send an email, do I need quotes?
Code:
if [ ${EXTRACT_FILES} = true ] ;then

vs
Code:
if [ ${EXTRACT_FILES = "true" ] ;then

, etc., etc. Do the spaces between variable and = matter? I know I need a space between the [ and ]. Thanks to all.

Last edited by Scrutinizer; 04-02-2012 at 01:13 PM.. Reason: Inserted Code tags
# 2  
Hi yes, the spaces do matter. ' is a strong quote and " is a weak quote. Within strong quotes variable do not get expanded, whereas with weak quotes they do. It is best to use double quotes around the variable reference on the left side...

Code:
if [ "${EXTRACT_FILES}" = true ] ;then

or

Code:
if [ "${EXTRACT_FILES}" = "true" ] ;then

# 3  
Wow - thanks for the quick response Scrutinizer! I'm going to look into that more. At least now I know to google strong quote and weak quote. I'm used to SQL where the variable values have ' ' around them, so the " " around the variable name is weird!
 

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