#!/bin/bash

for ((i = 10 ; i>=0 ; i--))
do
	echo $i
done

Syntax error: bad for loop variable

The reason is that since Ubuntu 6.10, Ubuntu has replaced the previous default bash shell with dash shell; It shows that the/bin/sh link reverses/bin/dash instead of the traditional/bin/bash.

Question 1: why #/ Bin/bash doesn’t work?

./execution will read #/ Bin/bash specifies the shell parser, and the script needs execution permission

Executing with SH will not read #/ Bin/bash, which is equivalent to executing the/bin/sh shell script and passing it in as a parameter. The script does not need execution permission, but only reading permission

Solution 1:

Execute sudo dpkg reconfigure dash and select No

Solution 2:

Modify cycle

for i in `seq 1 10`                                                                                                
do                                                                                                               
        echo $i                                                                                                  
done                                                                                                             
         
OR
                                                                                                        
for i in {0..10}                                                                                                 
do                                                                                                               
        echo $i                                                                                                  
done