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meaning of today=${1:-${today}}


 
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# 1  
Old 03-26-2012
meaning of today=${1:-${today}}

what does today=${1:-${today}} mean???

I saw a script which has these two lines:
today=`date '+%y%m%d'`
today=${1:-${today}}

but both gives the same value for $today

Code:
user:/export/home/user>today=`date '+%y%m%d'`
user:/export/home/user>echo $today
120326
user:/export/home/user>today=${1:-${today}}
user:/export/home/user>echo $today
120326
user:/export/home/user>today=
user:/export/home/user>today=${1:-${today}}
user:/export/home/user>echo $today
 
user:/export/home/user>

Can someone please let me know, what actually today=${1:-${today}}
means???
# 2  
Old 03-26-2012
If a parameter is given along with a script name while invoking it, then that parameter is considered, otherwise 'today' would contain `date +%y%m%d`.

For e.g., consider this script:
Code:
#! /bin/bash
today=`date '+%y%m%d'`
today=${1:-${today}}
echo $today

While invoking it, if you provide a parameter then variable 'today' would contain that parameter:
Code:
[user@host ~]$ ./test.sh 120331
120331

If you invoked the script without any parameters, then variable 'today' would hold today's date:
Code:
[user@host ~]$ ./test.sh
120326

This User Gave Thanks to balajesuri For This Post:
# 3  
Old 03-26-2012
thanks a lot balaje!!!!

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