[SOLVED] -gt: unary operator expected

hd_pulse · 05-26-2011, 02:25 PM

Quote:

echo "enter cost price of article"
read cp
echo "enter selling price of articel "
read sp
a= expr $sp - $cp
if [ $a -gt 0 ]
then
echo "PROFIT! "
echo "profit=" $a
else
echo "LOSS! "
echo "loss=" $(expr $cp - $sp)
fi

I wrote the abovee code to calculte the profit o loss made by the shopkeeper.

I gives error:

Quote:

enter cost price of article
65
enter selling price of articel
89
24
./10da: line 9: [: -gt: unary operator expected
LOSS!
loss= -24

Although it should print profit statement it prints loss statement.

It looks if[] statement is never being read.

Please explain the error.

anomie · 05-26-2011, 02:51 PM

Hints:

Your variable assignment is wonky.
It's normally a good idea to quote variables when doing logical tests.

crts · 05-26-2011, 03:10 PM

This is what anomie means.

Code:

a= expr $sp - $cp

There should be no space after the '='. Also read up on command substitution to solve this.

hd_pulse · 05-26-2011, 03:12 PM

Quote:

# It's normally a good idea to quote variables when doing logical tests.

Please show to quote in logical tests in the above code.

hd_pulse · 05-26-2011, 03:16 PM

Quote:

There should be no space after the '='. Also read up on command substitution to solve this.

After making the changes (as per ur suggestion ) it adds to the errors.

Quote:

enter cost price of article
43
enter selling price of articel
89
./10da: line 8: 89: command not found
./10da: line 9: [: -gt: unary operator expected
LOSS!
loss= -46

ie

Quote:

./10da: line 8: 89: command not found

another error is added.

crts · 05-26-2011, 03:27 PM

Quote:

Originally Posted by hd_pulse

After making the changes (as per ur suggestion ) it adds to the errors.

Did you use command substitution? Remember that
expr ...

is a command and you want the result to assign to a.

hd_pulse · 05-27-2011, 12:08 AM

Quote:

echo "enter cost price of article"
read cp
echo "enter selling price of articel "
read sp
a=expr $sp - $cp
if [ $a -gt 0 ]
then
echo "PROFIT! "
echo "profit=" $a
else
echo "LOSS! "
echo "loss=" $(expr $cp - $sp)
fi

this is what i wrote and it still gives the same error i.e

Quote:

./10da: line 9: [: -gt: unary operator expected

crts · 05-27-2011, 01:47 AM

Code:

a=expr $sp - $cp

You did not as suggested. Read my other post again. You only followed the first advice.

grail · 05-27-2011, 02:25 AM

My advice is to use the right tools for the job, remembering also that bash does not do decimal arithmetic:

Code:

echo "enter cost price of article"
read cp
echo "enter selling price of articel "
read sp
(( a = sp - cp ))
if (( a > 0 ))
then
    echo "PROFIT! "
    echo "profit=" $a
else
    echo "LOSS! "
    echo "loss=" $(( cp - sp ))
fi

Ramurd · 05-27-2011, 04:29 AM

What grail said, or use backticks / $() to get a command executed:

a=expr $sp - $cp

is going wrong; you saw this error:

Quote:

./10da: line 8: 89: command not found

which led to the next error; you were not assigning a proper value to the variable; and thus you get a "zero" variable-comparison which is being complained about.

You want to assign the value which is the outcome of the command; Hence, you need to tell the system that it is a command to be executed, like this:

a=`expr $sp - $cp` # using backticks
OR
a=$(expr $sp - $cp) # using $()

as a command execution; then you can do if [ $a -gt 0 ]

hd_pulse · 05-28-2011, 07:57 AM

Quote:

Originally Posted by Ramurd

a=`expr $sp - $cp` # using backticks
OR
a=$(expr $sp - $cp) # using $()

Thanks Man! It really worked.

Thanks Alot!