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1.12 Conventions ¶

In this book we have the following conventions:

• All commands that are to be run on the shell (command-line) prompt as the user start with a $. In case they must be run as a superuser 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 does not have any of the $ or # signs, then it is the output of the command after it is run. As a user, you do not 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.
• If the command becomes larger than the page width a \ is inserted in the code. If you are typing the code by hand on the command-line, you do not need to use multiple lines or add the extra space characters, so you can omit them. If you want to copy and paste these examples (highly discouraged!) then the \ should stay.

  The \ character is a shell escape character which is used commonly to make characters which have special meaning for the shell, lose that special meaning (the shell will not treat them especially if there is a \ behind them). When \ is the last visible character in a line (the next character is a new-line character) the new-line character loses its meaning. Therefore, the shell sees it as a simple white-space character not the end of a command! This enables 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 awk or 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.