Bash script operand expected

Question

I'm having a small problem with this following snippet and I'm not sure why. The error given is (line indicated):

*2: syntax error: operand expected (error token is "*2")

while [[ $numberServers -gt $newindex ]]; do
    serverPort=$((9001+$(($newindex*2))))      <--- This line
    clientPort=$(($serverPort+1))
    newindex=$(($newindex+1))
    localhostport=$((serverPort-2))

    string=$(($string,localhost:$(($serverPort-2))))
...

Any help would be greatly appreciated.

Sounds like $newindex didn't have the value you were expecting. What value does it have? — Etan Reisner
– Etan Reisner, Commented Nov 20, 2015 at 18:28
It does look as if $newindex is empty. You should probably test that it has a value before you use it in a formula. Also, too many parentheses! serverPort=$((9001+$newindex*2)) should do exactly the same thing. Similarly, newindex=$(($newindex+1)) can be replaced with ((newindex++)). — ghoti
– ghoti, Commented Nov 20, 2015 at 18:35
You're also misusing arithmetic expressions in the last line; presumably, you want to append the string localhost:$(($serverPort-2)) to the end of string. — chepner
– chepner, Commented Nov 20, 2015 at 18:46
@chepner How do you mean? I am now getting an error on that line so I agree, I just can't see how/where I am misusing the arithmetic? — sjwarner
– sjwarner, Commented Nov 20, 2015 at 19:15
I assume you want string="$string,localhost:$localhostport" or string+=",locahost:$localhostport". At best, $(($string,localhost:$locahostport)) would evaluate $string, discard the result, and evaluate to the next string. But arithmetic expressions are for just that: arithmetic, not string handling. Neither argument of the , operator is an arithmetic expression. — chepner
– chepner, Commented Nov 20, 2015 at 19:17

heemayl · Accepted Answer · 2015-11-20 18:29:59Z

3

The problem is that the variable newindex is empty, so the expression became:

$((9001+$((*2))))

check the initialization of newindex.

Example:

$ echo $((9001+$(($newindex*2))))
bash: *2: syntax error: operand expected (error token is "*2")

$ newindex=4

$ echo $((9001+$(($newindex*2))))
9009

answered Nov 20, 2015 at 18:29

heemayl

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6 Comments

sjwarner Over a year ago

Thank you! Silly mistake really. But now I'm getting another error? line 26: ,localhost:9001: syntax error: operand expected (error token is ",localhost:9001")

heemayl Over a year ago

@CAFC_Sam no problem..that seems like an syntax error..hard to tell without seeing the problematic line i.e. line 26..

sjwarner Over a year ago

line 26 is just string=$(($string,localhost:$(($serverPort-2))))

heemayl Over a year ago

@CAFC_Sam now string is empty..also its unclear to me what you are doing here ..

sjwarner Over a year ago

I have initialised string. I'm trying to just loop through a set of port numbers and add them all to the end of string, ready for a command line argument to a Java program

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