Why backslash before asterisk in `find`?

An unquoted glob would be expanded by the shell before find is executed. (Refer to Filename Expansion in the manual.)

So saying:

find . -name *.pyc -delete

would actually execute:

find . -name file1.pyc file2.pyc file3.pyc -delete

assuming there were 3 .pyc files in the current directory and result in an error instead.

A backslash makes the shell pass the glob to find, i.e. it acts as if *.pyc were quoted.

Ideally, you should be quoting a glob:

find . -name '*.pyc' -delete

Before your shell issues the find command, it will do various expansions. Doing so, it also processes special characters (or, characters with special meaning), where * is a wildcard – a globbing character. This is the so-called filename expansion.

Say you have two files in your directory:

• foo.pyc
• bar.pyc

Then *.pyc would expand to both names. So if you write:

find . -name *.pyc -delete

then the shell will actually call:

find . -name foo.pyc bar.pyc -delete

which does not make a lot of sense, because you can only have one argument for -name. That's why you need to escape the special character to prevent it from being interpreted by the shell. You do that by backslash-escaping, or alternatively, quoting it.