The backslash escapes the following newline, so the multiple lines will be treated as a single line.
Such syntax is usually used when lines would otherwise be long/unwieldy, to help readability and/or maintainability.
What you posted is the same as the single command:
Code:
sudo apt-get install ca-certificates curl gnupg lsb-release
This is described in
section 3.1 of the
Bash Manual (specifically
3.1.2.1) - it's a good idea for anyone using Bash to read
at least Section 3.1 to understand the basics.
(Also, whilst not relevant here, BashFAQ and ShellCheck are useful resources for anyone doing Bash scripting.)
