Syntax error: Bad for loop variable

问题

I'm trying to write a script that will vol up radio in the background

#!/bin/sh

for (( i = 80 ; i <= 101; i++ )) 
 do 
  amixer cset numid=1 i$% sleep 60;
done 

But i have problem:

alarmclock-vol.sh: 3: alarmclock-vol.sh: Syntax error: Bad for loop variable

回答1:

The for (( expr ; expr ; expr )) syntax is not available in sh. Switch to bash or ksh93 if you want to use that syntax. Otherwise, the equivalent for sh is:

#!/bin/sh

i=80
while [ "$i" -le 101 ]; do
    amixer cset numid=1 "$i%"
    sleep 60
    i=$(( i + 1 ))
done 

来源：https://stackoverflow.com/questions/30358065/syntax-error-bad-for-loop-variable