What is the meaning of `if [ "${-#*i}" != "$-"]`?

January 9, 2022

I was looking through the /etc/profile file and I noticed a strange if statement. Can someone let me know what this means?

I’m referring to the second if statement if [ "${-#*i}" != "$-"] .

for i in /etc/profile.d/*.sh /etc/profile.d/sh.local ; do
    if [ -r "$i" ]; then
        if [ "${-#*i}" != "$-" ]; then
            . "$i"
        else
            . "$i" >/dev/null
        fi
    fi
done

>Solution :

$- outputs the list of options the shell is running with. i in the output of $- means that the shell is interactive.

${var#expr} removes from the value of var the part from the left that matches the expr. expr is a glob. In the case expr is not matched, the original string is just outputted.

So ${-#*i} gets the value of $- and removes the part from the left that matches *i.

For example: $- is himBHs. The part that matches *i from the left is hi. So hi from the left will be removed. So ${-#*i} will be mBHs.

https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html https://www.gnu.org/software/bash/manual/html_node/The-Set-Builtin.html