linux - What is the difference between `./example.sh` and `sh example.sh`

Question

I am trying to play with bash and arrays. But executing a sample script, I got an unexpected syntax error message: example.sh: 3: example.sh: Syntax error: "(" unexpected. And this is the script

#!/bin/bash
array=( one two three )

If I run the script with ./example.sh it works and no errors are displayed. But if I run sh example.sh I get the error message.

I thought that these two commands are the same:

• sh example.sh
• ./example.sh

so ... what is the difference between the two?

Answer 1

When you launch it via ./example.sh then the command specified in the first line of the script is used to interpret the content. So your script executes in a bash, where such syntax is allowed for arrays.

When you launch it via sh example.sh then sh is the command that is used to interpret the content of the file. sh is the original Unix shell (aka Bourne shell) and this shell is a little more rude than bash (Bourne again shell). You don't have such arrays. Note that in sh the first line of your script is just interpreted as a comment.