In this book we have the following conventions:
$. In case they must be run as a super-user or system administrator, they will start with a single
#. If the command is in a separate line and next line
is also in the code type face, but doesn’t have any of the
#signs, then it is the output of the command after it is run. As a user, you don’t need to type those lines. A line that starts with
##is just a comment for explaining the command to a human reader and must not be typed.
The \ character is a shell escape character which is used commonly to make characters which have special meaning for the shell loose that special place (the shell will not treat them specially if there is a \ behind them). When it is a last character in a line (the next character is a new-line character) the new-line character looses its meaning an the shell sees it as a simple white-space character, enabling you to use multiple lines to write your commands.
This is not a convention, but a bi-product of the PDF building process of the manual:
In the PDF version of this manual, a single quote (or apostrophe) character in the commands or codes is shown like this:
Single quotes are sometimes necessary in combination with commands like
sed, or when using Column arithmetic in Gnuastro’s own Table (see Column arithmetic).
Therefore when typing (recommended) or copy-pasting (not recommended) the commands that have a
', please correct it to the single-quote (or apostrophe) character, otherwise the command will fail.