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44 GNU make

The ‘-s’ or ‘--silent’ ﬂag to make prevents all echoing, as if all recipes started with

‘@’. A rule in the makeﬁle for the special target .SILENT without prerequisites has the same

eﬀect (see Section 4.8 [Special Built-in Target Names], page 32). .SILENT is essentially

obsolete since ‘@’ is more ﬂexible.

5.3 Recipe Execution

When it is time to execute recipes to update a target, they are executed by invoking a new

sub-shell for each line of the recipe, unless the .ONESHELL special target is in eﬀect (see

Section 5.3.1 [Using One Shell], page 44) (In practice, make may take shortcuts that do not

aﬀect the results.)

Please note: this implies that setting shell variables and invoking shell commands such

as cd that set a context local to each process will not aﬀect the following lines in the recipe.

If you want to use cd to aﬀect the next statement, put both statements in a single recipe

line. Then make will invoke one shell to run the entire line, and the shell will execute the

statements in sequence. For example:

foo : bar/lose

cd $(@D) && gobble $(@F) > ../$@

Here we use the shell AND operator (&&) so that if the cd command fails, the script will fail

without trying to invoke the gobble command in the wrong directory, which could cause

problems (in this case it would certainly cause ../foo to be truncated, at least).

5.3.1 Using One Shell

Sometimes you would prefer that all the lines in the recipe be passed to a single invocation

of the shell. There are generally two situations where this is useful: ﬁrst, it can improve

performance in makeﬁles where recipes consist of many command lines, by avoiding extra

processes. Second, you might want newlines to be included in your recipe command (for

example perhaps you are using a very diﬀerent interpreter as your SHELL). If the .ONESHELL

special target appears anywhere in the makeﬁle then all recipe lines for each target will be

provided to a single invocation of the shell. Newlines between recipe lines will be preserved.

For example:

.ONESHELL:

foo : bar/lose

cd $(@D)

gobble $(@F) > ../$@

would now work as expected even though the commands are on diﬀerent recipe lines.

If .ONESHELL is provided, then only the ﬁrst line of the recipe will be checked for the

special preﬁx characters (‘@’, ‘-’, and ‘+’). Subsequent lines will include the special char-

acters in the recipe line when the SHELL is invoked. If you want your recipe to start with

one of these special characters you’ll need to arrange for them to not be the ﬁrst characters

on the ﬁrst line, perhaps by adding a comment or similar. For example, this would be a

syntax error in Perl because the ﬁrst ‘@’ is removed by make:

On MS-DOS, the value of current working directory is global, so changing it will aﬀect the following

recipe lines on those systems.

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Roland Ver. 4.5 Technical Information Seite 54