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Aa_app varible in Linux


 
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# 1  
Aa_app varible in Linux

Hi,

I am analyzing linux script, below is the following script line

Code:
 
${AA_APP:-/opt/ty/aa}/sbin/save_file_list ApplEnv.prererun ${AA_APP:-/opt/ty/aa}/sbin/ApplEnv.install_save_list

I really dont understand what this line does, can someone explain me.


AA_APP is variable assigning /opt/ty/aa directory?
# 2  
man bash:
Quote:
${parameter:-word}
Use Default Values. If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameter is substituted.
This User Gave Thanks to RudiC For This Post:
# 3  
Thanks, but still I dont understand does. why they are using two shell parameter. when I run this, its creating some file. but not getting exactly.

is it possible to explain me?
# 4  
Run command save_file_list from $AA_APP/sbin/ or, if AA_APP is NULL or unset, from /opt/ty/aa/sbin/ with first parameter ApplEnv.prererun and second parameter ${AA_APP}/sbin/ApplEnv.install_save_list or, if AA_APP is NULL or unset, /opt/ty/aa/sbin/ApplEnv.install_save_list. It looks to me as if the second par. might be a program to be run from within the command...
# 5  
Code:
${AA_APP:-/opt/ty/aa}/sbin/save_file_list......

AA_APP=/usr/share
Now the path would lead to /usr/share/sbin/save_file_list....
AA_APP=""
Now the path would lead to: /opt/ty/aa/sbin/save_file_list...

But saving a 'save_file_list' in a(ny) sbin path, isnt the best idea any way.

hth

Last edited by sea; 05-06-2015 at 01:52 PM..
 

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