Why should I provide two different paths when creating alias?

Question

When I issue alias --help I get this output:

alias: usage: alias [-p] [name[=value] ... ]

As I understand, all you need to do is to type an alias and provide the actual path to the script file, like this:

alias scr = /usr/local/tools/some_script.sh

However, I noticed that sometimes 2 paths are being provided when creating aliases - for example, I issued alias scr command on a corporate machine and got this output:

alias scr = 'sudo /bin/sh /usr/local/tools/some_script.sh'

What is the purpose of introducing additional path /bin/sh in this case?

The /bin/sh contains only a symlink to bash directory:

ls -l /bin/sh
lrwxrwxrwx 1 root root 4 Aug  6  2017 /bin/sh -> bash

Answer 1

The alias defined through

alias scr='sudo /bin/sh /usr/local/tools/some_script.sh'

(having spaces around the = is an error), calls sudo which in turn runs the script /usr/local/tools/some_script.sh by explicitly calling the /bin/sh shell interpreter with the script's pathname as an argument.

The /bin/sh is the pathname of the sh executable under /bin (in your case it's a symbolic link to bash, but that's unimportant). It is used to run sh shell scripts. In this case, the script at /usr/local/tools/some_script.sh is presumably a script written for sh, so the alias makes sure that it's called with /bin/sh as the interpreter.

If the script is executable and has a #!-line that points to a valid script interpreter as its first line, the /bin/sh bit can be removed.

So, in short, the alias allows you to run the command

/bin/sh /usr/local/tools/some_script.sh

as root by just typing scr.