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In my Makefile, I need to test if the current directory is an SVN repo or not and if it is not I want to indicate an error using the $(error) directive in Makefile.
So I plan to use the return value of $(shell svn info .) but I'm not sure how to get this value from within the Makefile.
Note: I'm not trying to get the return value in a recipe, but rather in the middle of the Makefile.
Right now I'm doing something like this, which works just because stdout is blank when it is an error:
SVN_INFO := $(shell svn info . 2> /dev/null) ifeq ($(SVN_INFO),) $(error "Not an SVN repo...") endif I'd still like to find out if it is possible to get the return value instead within the Makefile.
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The return value of a command is stored in the $? variable. The return value is called exit status. This value can be used to determine whether a command completed successfully or unsuccessfully.
“$?” is a variable that holds the return value of the last executed command. “echo $?” displays 0 if the last command has been successfully executed and displays a non-zero value if some error has occurred. The bash sets “$?” To the exit status of the last executed process.
Every command returns an exit status (sometimes referred to as a return status or exit code). A successful command returns a 0, while an unsuccessful one returns a non-zero value that usually can be interpreted as an error code.
How about using $? to echo the exit status of the last command?
SVN_INFO := $(shell svn info . 2> /dev/null; echo $$?) ifeq ($(SVN_INFO),1) $(error "Not an SVN repo...") endif
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If you want to preserve the original output then you need to do some tricks. If you are lucky enough to have GNU Make 4.2 (released on 2016-05-22) or later at your disposal you can use the .SHELLSTATUS variable as follows.
var := $(shell echo "blabla" ; false) ifneq ($(.SHELLSTATUS),0) $(error shell command failed! output was $(var)) endif all: @echo Never reached but output would have been $(var) Alternatively you could use a temporary file or play with Make's eval to store the string and/or the exit code into a Make variable. The example below gets this done but I would certainly like to see a better implementation than this embarrassingly complicated version.
ret := $(shell echo "blabla"; false; echo " $$?") rc := $(lastword $(ret)) # Remove the last word by calculating <word count - 1> and # using it as the second parameter of wordlist. string:=$(wordlist 1,$(shell echo $$(($(words $(ret))-1))),$(ret)) ifneq ($(rc),0) $(error shell command failed with $(rc)! output was "$(string)") endif all: @echo Never reached but output would have been \"$(string)\" If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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