strange errors on bash script

Question

Warning: I just started learning bash recently and trying to do a recursive function that will calculate a term...so...

x0 = 0 x1 = 1 xm = 3 * xm-1 - 2 * xm-2

The function I wrote so far is:

#!/bin/bash
calculate()
{
 if [ $1 -eq 0 ]
 then
 echo "0"
 fi
 if [ $1 -eq 1 ]
 then
 echo "1"
 fi
 if [ $1 -ge 1 ]
 then
 let var1 = `calculate [ $1-1 ]`;
 let var2 = `calculate [ $1-2 ]`;
 let var3 = 3*var1-2*var2;
 echo var3
fi
}
calculate 3

But I get some strange errors...and not sure if I did it correctly...can anyone tell me what causes these issues and correct my code so it works? Thank you so much.

Errors:

TP1p1.sh: line 4: [: [: integer expression expected
TP1p1.sh: line 8: [: [: integer expression expected
TP1p1.sh: line 12: [: [: integer expression expected
TP1p1.sh: line 14: let: =: syntax error: operand expected (error token is "=")
TP1p1.sh: line 4: [: [: integer expression expected
TP1p1.sh: line 8: [: [: integer expression expected
TP1p1.sh: line 12: [: [: integer expression expected
TP1p1.sh: line 15: let: =: syntax error: operand expected (error token is "=")
TP1p1.sh: line 16: let: =: syntax error: operand expected (error token is "=")

anubhava · Accepted Answer · 2012-03-26 21:53:00Z

3

Well not sure about your calculation but your syntactically cleaned up base script is this one:

#!/bin/bash
calculate() {
 if [ $1 -eq 0 ]; then
    echo -n "0"
 elif [ $1 -eq 1 ]; then
    echo -n "1"
 elif [ $1 -ge 1 ]; then
    var1=$( calculate $(($1-1)) )
    var2=$( calculate $(($1-2)) )
    var3=$((3*(var1-2)*var2))
    echo $var3
fi
}
calculate 5

answered Mar 26, 2012 at 21:53

anubhava

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2 Comments

FinalDestiny Over a year ago

it's working just for 5, for 3 it shows -6 and for 6 it shows 0. :-(

FinalDestiny Over a year ago

Sorry, your code is correct but var3=$((3*(var1-2)*var2)) is wrong, it should be $(( (3*var1) - (2*var2) ))

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