Roland Ver. 4.5 Informações Técnicas descarregar pdf (Página 59)

Chapter 5: Writing Recipes in Rules 49

modes). For example, many programs that can display colorized output will not do so

if they determine they are not writing to a terminal. If your makeﬁle invokes a program

like this then using the output synchronization options will cause the program to believe

it’s running in “non-interactive” mode even though the output will ultimately go to the

terminal.

5.4.2 Input During Parallel Execution

Two processes cannot both take input from the same device at the same time. To make

sure that only one recipe tries to take input from the terminal at once, make will invalidate

the standard input streams of all but one running recipe. If another recipe attempts to read

from standard input it will usually incur a fatal error (a ‘Broken pipe’ signal).

It is unpredictable which recipe will have a valid standard input stream (which will come

from the terminal, or wherever you redirect the standard input of make). The ﬁrst recipe

run will always get it ﬁrst, and the ﬁrst recipe started after that one ﬁnishes will get it next,

and so on.

We will change how this aspect of make works if we ﬁnd a better alternative. In the

mean time, you should not rely on any recipe using standard input at all if you are using

the parallel execution feature; but if you are not using this feature, then standard input

works normally in all recipes.

5.5 Errors in Recipes

After each shell invocation returns, make looks at its exit status. If the shell completed

successfully (the exit status is zero), the next line in the recipe is executed in a new shell;

after the last line is ﬁnished, the rule is ﬁnished.

If there is an error (the exit status is nonzero), make gives up on the current rule, and

perhaps on all rules.

Sometimes the failure of a certain recipe line does not indicate a problem. For example,

you may use the mkdir command to ensure that a directory exists. If the directory already

exists, mkdir will report an error, but you probably want make to continue regardless.

To ignore errors in a recipe line, write a ‘-’ at the beginning of the line’s text (after the

initial tab). The ‘-’ is discarded before the line is passed to the shell for execution.

For example,

clean:

-rm -f *.o

This causes make to continue even if rm is unable to remove a ﬁle.

When you run make with the ‘-i’ or ‘--ignore-errors’ ﬂag, errors are ignored in all

recipes of all rules. A rule in the makeﬁle for the special target .IGNORE has the same eﬀect,

if there are no prerequisites. These ways of ignoring errors are obsolete because ‘-’ is more

ﬂexible.

When errors are to be ignored, because of either a ‘-’ or the ‘-i’ ﬂag, make treats an

error return just like success, except that it prints out a message that tells you the status

code the shell exited with, and says that the error has been ignored.

When an error happens that make has not been told to ignore, it implies that the

current target cannot be correctly remade, and neither can any other that depends on it

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