yarn install script has issues when running in dash

[interone-ms]

Bug description

When running the yarn install.sh script in a system set with dash as sh shell, there are errors during installation displayed, as the installation script uses bashisms.

Command

./install.sh

What is the current behavior?

install.sh outputs warnings:

install.sh: 52: [[: not found
install.sh: 57: [: unexpected operator
install.sh: 95: [[: not found

What is the expected behavior?
The installer should run without warnings.

Steps to Reproduce

1. curl -L -o install.sh https://yarnpkg.com/install.sh
2. chmod +x install.sh && ./install.sh

Environment

• Node Version: n/a
• Yarn v1 Version: 1.19.2
• OS and version: any os with dash shell

[Daniel15]

Would you like to submit a PR to fix this?