linux - what is meaning of export in multiple-line variable -

what meaning of export in multiple-line variable?

in example command export foo or not, output 'welcome'.

define foo   echo welcome endef export foo all:       @$(foo) 

variable values of top-level make can passed sub-make(sub directory makefile) through environment explicit request. these variables defined in sub-make defaults.

the special variables shell , makeflags exported (unless unexport them).

if want export specific variables sub-make, use export directive, this:

export variable

if want prevent variable being exported, use unexport directive, this:

unexport variable