Use a curlbash script for installing swiftly

[marcprux]

Motivation:

The current recommendation for installing Swiftly on macOS and Linux involves a gnarly multi-line shell-specific blob of code that the user needs to paste into their shell.

Curlbash scripts (i.e., curl https://… | sh) are a common and portable way to install software for UNIX-like systems. They are used by popular packages like rbenv, Homebrew, Rust, NVM, Tailscale, and Deno.

Modifications:

Add a swiftly-install shell script for installing swiftly and recommend using it from the "Install" pages.

Result:

The installation instructions will be briefer and nicer and not require that the user know what shell they are running.

Before:

After:

[jakepetroules]

Use #!/bin/sh for maximum portability? shellcheck can help validate.

[marcprux]

soundness.sh seems to prefer bash

[jakepetroules]

On Linux, almost no command line tool is guaranteed to be installed. It's worth checking if all of the programs the script needs are installed.

• ps (from a package usually called procps) is not always present.
• tar is not always present.
• Neither is curl (yes the swift.org instructions propose fetching the script with curl in the first place, but someone might've still manually used wget or something other way to get the script onto their machine)

mktemp and uname come from coreutils, but those are a bit too fundamental to bother checking for IMO. cd is a shell builtin.

Or, you could detect apt-get and dnf and try to install the relevant packages to ensure they'll be there (without -y, so the user is prompted if configured).

something like this:

if command -v apt-get >/dev/null 2>&1 ; then # debian, ubuntu
    apt-get update
    apt-get install curl procps tar
elif command -v dnf >/dev/null 2>&1 ; then # rhel
    dnf update
    dnf install curl procps tar
elif command -v yum >/dev/null 2>&1 ; then # amazonlinux2
    yum update
    yum install curl procps tar
elif ! command -v curl >/dev/null 2>&1 || ! command -v ps >/dev/null 2>&1 || ! command -v tar >/dev/null 2>&1 ; then
    echo "Missing one of more of the following programs: curl, ps, tar" >&2
    exit 1
fi

[marcprux]

Good call. I think that automatically running their package manager to install the missing utilities is a bit heavy-handed, so I just went with the fail-fast exit when one of the necessary commands is not present.