makefile: trailing spaces in variable value

Question

I'm reading the following in GNU make manual:

if you do not want any whitespace characters at the end of your variable value, 
you must remember not to put a random comment on the end of the line after some whitespace, such as this:

 dir := /foo/bar    # directory to put the frobs in
Here the value of the variable dir is ‘/foo/bar    ’ (with four trailing spaces), 
which was probably not the intention. (Imagine something like ‘$(dir)/file’ with this definition!)

I tried with a simple makefile as below"

foo := hi    # four trailing spaces
all:
    @echo $(foo)_

when executing 'make', the output is just 'hi _', only one space between 'hi' and underscore. Why there are no four spaces?

Thanks,

William Breathitt Gray · Accepted Answer · 2013-06-04 14:10:20Z

3

When make executes this script, it doesn't pass a variable to the echo, but instead replaces $(foo) with foo's value.

So the actual script executed is echo hi...._ (dots are for clarification).

And the white spaces just ignored when parsing the arguments for echo.

You can put double quotes around to make it output as a string.

echo "$(foo)_"

edited Jun 4, 2013 at 14:10

William Breathitt Gray

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answered Nov 12, 2012 at 10:49

xiaoyi

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1 Comment

password636 Over a year ago

yes. It's shell who "swallow" the spaces, I got it. Thank you very much!

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