Continuous tab in indentation could cause problem

When I tested the following code in terminal and got an error at the 2nd echo. It asked to list all files in the current folder, e.g. “Display all 148 possibilities? (y or n)”, rather than moving forwards. I cannot tell any error in the code.

for i in 1 2 3 4 5
do
    echo $i
    for j in eRNA promoter exon random
    do
        echo $j
    done
done

I figure it out when I display all the white characters, as shown below:

Do you see the difference?

The “working” code, which I copied from the Linux document (http://www.tldp.org/LDP/abs/html/nestedloops.html) has different characters for the nested indentation (-> .. means a tab and two spaces) than the two tabs in the “not working” part (which I typed in Rstudio). I realized that it’s because the tab-autocompletion feature in Linux. Pressing tab a second time will tell the shell to provide a list of matching files.

To avoid the problem, simply click on the “Insert spaces for tab” option in your editor. I used Rstudio, here is where you can find the option: