Dependency line syntax
A dependency line has the form:
target1[target2 ...]:[:][dependent1 ...][; commands][# ...]
[ \t commands] [# ...]
. . .
Items inside brackets may be omitted. Targets and dependents are
strings of letters, digits, periods, and slashes.
Shell meta-characters such as * and ? are expanded
when the line is evaluated.
Commands appear either after a semicolon on a dependency line
or on lines beginning with tabs immediately following a dependency line.
A command is any string of characters not including a number sign (#),
except when the number sign is in quotes.
A number sign (#) denotes a comment line. All characters after the number sign, on the same line, are ignored. Blank lines are ignored.
If a non-comment line is too long, it can be continued by using a backslash ``\'' at the end of the line. However, if the last character on a line is a backslash, then it and everything following it is replaced by a single blank.