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Shell Programming and Scripting

Variable on If Statement

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# 1  
Old 12-20-2012
Variable on If Statement
Hi,

I am tasked to modify soem script and I come accross a line which I dont fully understand. I tried searching online but I couldnt get a good explanation on it.

Here it the part of the code:

Code:
 
PAY_RT=`cat $TEMPFILE | cut -f2 -d","`
 
if [ ${PAY_RT:-BLANK = 'P' ];
then
     PAY_RT=R
fi

What is the colon (:) and hypen (-) means on the if statement? I never used this on any of my if statement before.

There are also variation of :
Code:
if [ ${PAY_AMNT:-"00" = "000" ];
then
     PAY_AMNT=00
fi

# 2  
Old 12-20-2012
It is called "parameter expansion".

An extract from the Korn shell man page:

Quote:
${parameter:-word}
If parameter is set and is non-null then substitute its value; otherwise substitute word.
Although your code seems to be missing the closing }.
# 3  
Old 12-20-2012
Anything of the form ${...}is a bash parameter substitution, the one you are seeing should read ${PAY_AMNT:-"00"} and could be read substitute this marker with the value of PAY_AMNT or if PAY_AMNT is null use "00"
# 4  
Old 12-20-2012
That really helps! Thanks.
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