"operand expected" in bash script-CodePudding

#!/bin/bash

echo 'Users for system Alderaan: '
read 'Ald'
echo 'Users for system Coruscant: '
read 'Cor'
echo 'Users for system Endor: '
read 'End'
echo 'Users for system Hoth: '
read 'Hot'
echo 'Users for system Tatooine: '
read 'Tat'

echo SUM=$(($Ald   $Cor   $End   $Hot   $Tat))
echo AVG=$(($SUM / 5))

Users for system Alderaan: 
4
Users for system Coruscant: 
4
Users for system Endor: 
4
Users for system Hoth: 
4
Users for system Tatooine: 
4
SUM=20
./starwars: line 15: / 5: syntax error: operand expected (error token is "/ 5")

I've tried a few different ways for the "5" but I can't seem to figure it out.

CodePudding user response：

The problem is that this line ...

echo SUM=$(($Ald   $Cor   $End   $Hot   $Tat))

... does not contain an assignment to SUM. It just prints output that resembles a shell assignment. Therefore, on the next line ...

echo AVG=$(($SUM / 5))

... $SUM expands to nothing, leaving you attempting to evaluate "/ 5" as an arithmetic expression.

Try this instead:

SUM=$(($Ald   $Cor   $End   $Hot   $Tat))
echo SUM=$SUM
echo AVG=$(($SUM / 5))

And note that there is no assignment to AVG, either, but that doesn't matter because you are not attempting to use any such variable.

CodePudding user response：

You're never setting the SUM variable. You're printing out (echo) a command which would set the SUM variable if you were to run that command, but you're not running that command, just printing it.

echo <... something ...>

will just print <... something ...>, it won't actually run <... something ...>. To run <... something ...> literally just put

<... something ...>