diff options
| -rw-r--r-- | make.texinfo | 31 |
1 files changed, 25 insertions, 6 deletions
diff --git a/make.texinfo b/make.texinfo index af69e05..c26a5ec 100644 --- a/make.texinfo +++ b/make.texinfo @@ -2213,12 +2213,12 @@ foo : bar/lose The program used as the shell is taken from the variable @code{SHELL}. By default, the program @file{/bin/sh} is used. -Unlike most variables, the variable @code{SHELL} will not be set from -the environment, except in a recursive @code{make}. This is because the -@code{SHELL} environment variable is used to specify your personal -choice of shell program for interactive use. It would be very bad for -personal choices like this to affect the functioning of makefiles. -@xref{Environment, ,Variables from the Environment}. +Unlike most variables, the variable @code{SHELL} is never set from the +environment. This is because the @code{SHELL} environment variable is +used to specify your personal choice of shell program for interactive +use. It would be very bad for personal choices like this to affect +the functioning of makefiles. @xref{Environment, ,Variables from the +Environment}. @node Parallel, Errors, Execution, Commands @section Parallel Execution @@ -3570,6 +3570,25 @@ Expand all variable references in @var{arg1} and @var{arg2} and compare them. If they are identical, the @var{text-if-true} is effective; otherwise, the @var{text-if-false}, if any, is effective. +Often you want to test if a variable has a non-empty value. When the +value results from complex expansions of variables and functions, +expansions you would consider empty may actually contain whitespace +characters and thus are not seen as empty. However, you can use the +@code{strip} function to avoid interpreting whitespace as a non-empty +value. For example: + +@example +@group +ifeq ($(strip $(foo)),) +@var{text-if-empty} +endif +@end group +@end example + +@noindent +will evaluate @var{text-if-empty} even if the expansion of +@code{$(foo)} contains whitespace characters. + @item ifneq (@var{arg1}, @var{arg2}) @itemx ifneq '@var{arg1}' '@var{arg2}' @itemx ifneq "@var{arg1}" "@var{arg2}" |