How to abort makefile if variable not set

Question

How could I abort a make makefile execution based on a makefile s variable not being set valued   I came up with this  but works only if caller doesn t explicitly run a target  i e  runs make only    ifeq    MY FLAG    abort       This MUST be the first target    ugly      echo Variable MY FLAG not set  amp  amp  false endif  all       echo MY FLAG   MY FLAG    I think something like this would be a good idea  but didn t find anything in make s manual   ifndef MY FLAG  ABORT endif

User · Answer

Use the shell error handling for unset variables (note the double $):

$ cat Makefile
foo:
        echo "something is set to $${something:?}"

$ make foo
echo "something is set to ${something:?}"
/bin/sh: something: parameter null or not set
make: *** [foo] Error 127


$ make foo something=x
echo "something is set to ${something:?}"
something is set to x

If you need a custom error message, add it after the ?:

$ cat Makefile
hello:
        echo "hello $${name:?please tell me who you are via \$$name}"

$ make hello
echo "hello ${name:?please tell me who you are via \$name}"
/bin/sh: name: please tell me who you are via $name
make: *** [hello] Error 127

$ make hello name=jesus
echo "hello ${name:?please tell me who you are via \$name}"
hello jesus

User · Answer

TL DR  Use the error function   ifndef MY FLAG   error MY FLAG is not set  endif   Note that the lines must not be indented  More precisely  no tabs must precede these lines     Generic solution  In case you re going to test many variables  it s worth defining an auxiliary function for that     Check that given variables are set and all have non-empty values    die with an error otherwise      Params      1  Variable name s  to test      2   optional  Error message to print  check defined           strip   foreach 1  1              call   check defined  1   strip   value 2        check defined           if   value  1              error Undefined  1  if  2    2       And here is how to use it      call check defined  MY FLAG     call check defined  OUT DIR  build directory    call check defined  BIN DIR  where to put binary artifacts    call check defined                LIB INCLUDE DIR               LIB SOURCE DIR            library path     This would output an error like this   Makefile 17      Undefined OUT DIR  build directory    Stop    Notes   The real check is done here     if   value  1     error         This reflects the behavior of the ifndef conditional  so that a variable defined to an empty value is also considered  undefined   But this is only true for simple variables and explicitly empty recursive variables     ifndef and check defined consider these UNDEFINED  explicitly empty   simple empty      explicitly empty     ifndef and check defined consider it OK  defined   recursive empty     explicitly empty    As suggested by  VictorSergienko in the comments  a slightly different behavior may be desired        if   value  1  tests if the value is non-empty  It s sometimes OK if the variable is defined with an empty value  I d use   if   filter undefined   origin  1         And      Moreover  if it s a directory and it must exist when the check is run  I d use   if   wildcard  1    But would be another function    Target-specific check  It is also possible to extend the solution so that one can require a variable only if a certain target is invoked     call check defined       from inside the recipe  Just move the check into the recipe    foo           call check defined  BAR  baz value      The leading   sign turns off command echoing and   is the actual command  a shell no-op stub   Showing target name  The check defined function can be improved to also output the target name  provided through the    variable    check defined           strip   foreach 1  1              call   check defined  1   strip   value 2        check defined           if   value  1                error Undefined  1  if  2    2    if   value                       required by target           So that  now a failed check produces a nicely formatted output   Makefile 7      Undefined BAR  baz value  required by target  foo    Stop    check-defined-MY FLAG special target  Personally I would use the simple and straightforward solution above  However  for example  this answer suggests using a special target to perform the actual check  One could try to generalize that and define the target as an implicit pattern rule     Check that a variable specified through the stem is defined and has   a non-empty value  die with an error otherwise           The name of the variable to test       check-defined-      check defined FORCE         call check defined      target-specific     Since pattern rules can t be listed as prerequisites of  PHONY    we use the old-school and hackish FORCE workaround    You could go without this  but otherwise a check can be missed   in case a file named like  check-defined-     exists in the root    directory  e g  left by an accidental  make -t  invocation   PHONY     check defined FORCE   check defined FORCE     Usage     foo   check-defined-BAR    Notice that the check-defined-BAR is listed as the order-only        prerequisite   Pros     arguably  a more clean syntax   Cons    One can t specify a custom error message Running make -t  see Instead of Executing Recipes  will pollute your root directory with lots of check-defined-    files  This is a sad drawback of the fact that pattern rules can t be declared  PHONY    I believe  these limitations can be overcome using some eval magic and secondary expansion hacks  although I m not sure it s worth it

User · Answer

You can use an IF to test   check                var          echo   gt  gt  var is not set   exit 1     Result     make check  gt  gt  var is not set Makefile 2  recipe for target  check  failed make       check  Error 1

User · Answer

Use the shell function test   foo      test   something    Usage     make foo test  Makefile 2  recipe for target  foo  failed make       foo  Error 1   make foo something x test x

User · Answer

For simplicity and brevity     cat Makefile check-                if   value        error    is undefined    bar   check-foo         echo  foo is   foo    With outputs     make bar Makefile 2      foo is undefined  Stop    make bar foo  something  echo  foo is   foo  foo is something

[makefile] How to abort makefile if variable not set?

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