In GNU Make, how do I convert a variable to lower case?
MakefileMakefile Problem Overview
This is a silly question, but.... with GNU Make:
VAR = MixedCaseText
LOWER_VAR = $(VAR,lc)
default:
@echo $(VAR)
@echo $(LOWER_VAR)
In the above example, what's the correct syntax for converting VAR's contents to lower case? The syntax shown (and everything else I've run across) result in LOWER_VAR being an empty string.
Makefile Solutions
Solution 1 - Makefile
you can always spawn off tr
LOWER_VAR = `echo $(VAR) | tr A-Z a-z`
or
LOWER_VAR = $(shell echo $(VAR) | tr A-Z a-z)
The 'lc' functions you trying to call is from GNU Make Standard Library
Assuming that is installed , the proper syntax would be
LOWER_VAR = $(call lc,$(VAR))
Solution 2 - Makefile
You can do this directly in gmake, without using the GNU Make Standard Library:
lc = $(subst A,a,$(subst B,b,$(subst C,c,$(subst D,d,$(subst E,e,$(subst F,f,$(subst G,g,$(subst H,h,$(subst I,i,$(subst J,j,$(subst K,k,$(subst L,l,$(subst M,m,$(subst N,n,$(subst O,o,$(subst P,p,$(subst Q,q,$(subst R,r,$(subst S,s,$(subst T,t,$(subst U,u,$(subst V,v,$(subst W,w,$(subst X,x,$(subst Y,y,$(subst Z,z,$1))))))))))))))))))))))))))
VAR = MixedCaseText
LOWER_VAR = $(call lc,$(VAR))
all:
@echo $(VAR)
@echo $(LOWER_VAR)
It looks a little clunky, but it gets the job done.
If you do go with the $(shell) variety, please do use :=
instead of just =
, as in LOWER_VAR := $(shell echo $VAR | tr A-Z a-z)
. That way, you only invoke the shell one time, when the variable is declared, instead of every time the variable is referenced!
Hope that helps.
Solution 3 - Makefile
To handle capital letters with accents:
LOWER_VAR = $(shell echo $VAR | tr '[:upper:]' '[:lower:]')
Results:
$ VAR="Éclipse"
$ echo $VAR | tr A-Z a-z
Éclipse
$ echo $VAR | tr '[:upper:]' '[:lower:]'
éclipse
Solution 4 - Makefile
I find this slightly cleaner...
$(shell tr '[:upper:]' '[:lower:]' <<< $(VAR))
Solution 5 - Makefile
If Python is installed this runs even on Windows:
$(shell python -c "print('$(VAR)'.lower())")
Solution 6 - Makefile
GNU make doesn't include string functions for case conversion. Thus, there is no lc
function defined, by default.
But GNU Make usually comes with GNU Guile support enabled (e.g. this is the case on Fedora 33).
Thus, you can just call a Guile function for converting the case:
VAR = MixedCaseText
LOWER_VAR = $(guile (string-downcase "$(VAR)"))
default:
@echo $(VAR)
@echo $(LOWER_VAR)
Or if you want to encapsulate the Guile call:
VAR = MixedCaseText
LOWER_VAR = $(call to_lower,$(VAR))
define to_lower
$(guile (string-downcase "$(1)"))
endef
default:
@echo $(VAR)
@echo $(LOWER_VAR)