Passing asterisk As A Parameter


 
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# 1  
Old 07-11-2008
Error Passing asterisk As A Parameter

I have written a Shell Script Program which accepts 3 parameters as shown below:

Code:
./calc 20 + 2

in the above line ./calc is the Shell Script itself with 3 parameters, namely:

20
+
and 2.

Well, now let's look inside the Script:

Code:
result=$1$2$3
echo $result

The output will be as per our expectation:

Code:
22

But well, let's change the sign in the 2nd parameter being passed:

Code:
./calc 20 - 2

Code:
./calc 20 / 2

All those there examples have no issues so far!

But when we pass * as a parameter
Code:
./calc 20 * 2

things go bad!

Instead of *, the result of "ls *" command or simply the directory list gets passed to the variable: $2.

So, how can I make this Calculator program a user friendly one? I have been suggested to use '*' (I have not tried it yet, however) but it doesn't seem to be a User Friendly Way of writing any script or program, does it?

Thanks!

Dev.
# 2  
Old 07-11-2008
Escape the asterisk
Code:
./calc 20 \* 2

# 3  
Old 07-11-2008
try
Code:
./calc bill \* gates

and you'll get a ls listing again. Escaping the asterisk only seems to work on numerals. Does anyone know a workaround?
# 4  
Old 07-11-2008
If you have the bc package installed, this script works:
Code:
#!/bin/sh
echo "$@" | bc

But you do have to quote the asterisk as suggested: calc 20 \* 2

BTW, try using your script in a directory that has no files. That is, try this:

mkdir empty
cd empty
../calc 20 * 2
cd ..
rmdir empty
# 5  
Old 07-11-2008
Quote:
Originally Posted by na5m
try
Code:
./calc bill \* gates

and you'll get a ls listing again. Escaping the asterisk only seems to work on numerals. Does anyone know a workaround?
If typing an extra command before & after you're done using the 'calc' utility is acceptable, you could type "set -f" first... ("set +f" to set it back when you're done)...
(Unfortunately, putting this command inside your script won't work, since by the time the script is executed, the * special character will already be expanded...)
# 6  
Old 07-18-2008
Well, I tried this code segment:

Code:
./calc 10 '*' 5

and also this one

Code:
./calc 10 "*" 5

and both of them worked. But it is not user-friendly, is it?
# 7  
Old 07-18-2008
One thing you might try is using the double parens math workings of bash. Quite cool and is readable, and it avoids your shell expansion problem. Secondarily, a "here" document with the "dc" program is how I used to do it. e.g.:

dc <<EOF
2 20 * p
EOF
will produce 40 as output

Using the double-parens syntax of bash, one can do this:

$i=0
((i=2*20))
echo $i <-- produces 40

Kinda cool, huh?

Last edited by fsahog; 07-18-2008 at 11:47 PM.. Reason: To illustrate more fully
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