A puzzel about sh and ./

Question

I have figured that if I want to use./to execute a script, I have to runchmod +x filefirst. But why can I execute it by using sh file without the chmod command? Doesn't sh need any executing permission?

In the second case, it only needs to be readable. See What is the difference between sh and ./ when invoking a shell script? — steeldriver, Mar 18 '20 at 12:06

Rinzwind · Accepted Answer · 2020-03-18T12:14:46.683

1

sh HAS execution permissions. Well it basically is a symlink to dash.

$ ls -l /bin/sh
lrwxrwxrwx 1 root root 4 Feb 17  2016 /bin/sh -> dash

And dash has execute permissions:

$ ls -l /bin/dash
-rwxr-xr-x 1 root root 154072 Feb 17  2016 /bin/dash

All dash has to do is parse the script so the file needs to be readable.

edited Mar 18 '20 at 12:14

answered Mar 18 '20 at 12:04

Rinzwind

299,756

Then why ./ need execution permission? Doesn't it work like sh? – Shengyu Liu Mar 18 '20 at 12:21
How would you differentiate between listing the file on screen and executing it contents? There needs to be a way to tell the file to execute and you do that with ./ + executing permissions. (The latter is more a security measure: being able to execute anything is bad). – Rinzwind Mar 18 '20 at 12:26

A puzzel about sh and ./

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