CODEWITHSUNDEEP
gnu-make
CodeYoddha
CodeYoddha

Reputation: 21

Chained string substitions in gmake

In GNU make, I'd like to perform multiple string substitutions on a blob of text containing several "placeholders", e.g.:

MYTEXT:= blabla _FIRST_PLACEHOLDER_ blabla _SECOND_PLACEHOLDER_whateverblabla_THIRD_PLACEHOLDER_blablabla

So I'd like to replace the "placeholders" with values as follows:

_FIRST_PLACEHOLDER_ => FIRST_VAL
_SECOND_PLACEHOLDER_ => SECOND_VAL
_THIRD_PLACEHOLDER_ => THIRD_VAL
...

The following shows a hideous way of obtaining the result I'd like:

$(subst _FIRST_PLACEHOLDER_,FIRST_VAL, $(subst _SECOND_PLACEHOLDER_,SECOND_VAL, $(subst _THIRD_PLACEHOLDER_,THIRD_VAL, $(MYTEXT))))

A solution would be straightforward to find outside the make world, but is there a better way than the above to perform such a recursive substitution while remaining within the confines of make? I tried using $(foreach), but this simply concatenates the result of each substitution applied once to the initial $(MYTEXT).

Upvotes: 2

Views: 54

Answers (1)

Stefan Becker
Stefan Becker

Reputation: 5962

Iterative solution

This solution requires overwriting of the variables _p and _x.

# -*- gnu-make -*-
ORIGINAL         := 123__PLACE_HOLDER__1567__PLACE_HOLDER__2890
REPLACEMENT_LIST :=       \
    __PLACE_HOLDER__1=ABC \
    __PLACE_HOLDER__2=DEF \

_replace1 = $(eval _x := $(subst $(word 1,$(1)),$(word 2,$(1)),$(_x)))
replace   = $(strip \
    $(eval _x := $(strip $(2))) \
    $(foreach _p,$(strip $(1)),$(call _replace1,$(subst =, ,$(_p)))) \
    $(_x) \
    $(eval _x :=) \
)

$(info ORIGINAL:    '$(ORIGINAL)')
$(info REPLACEMENT: '$(call replace,$(REPLACEMENT_LIST),$(ORIGINAL))')

.PHONY: all
all:

Example run:

$ make 
ORIGINAL:    '123__PLACE_HOLDER__1567__PLACE_HOLDER__2890'
REPLACEMENT: '123ABC567DEF890'
make: Nothing to be done for 'all'.

Recursive solution

This solution has the advantage of not modifying any variable.

_replace2 = $(subst $(word 1,$(1)),$(word 2,$(1)),$(2))
_replace1 = $(call replace,$(2),$(call _replace2,$(subst =, ,$(1)),$(3)))
replace   = $(if $(1),$(call _replace1,$(firstword $(1)),$(wordlist 2,1000000,$(1)),$(2)),$(2))

or

_replace1 = $(subst $(word 1,$(1)),$(word 2,$(1)),$(2))
replace   = $(if $(1),$(call replace,$(wordlist 2,1000000,$(1)),$(call _replace1,$(subst =, ,$(firstword $(1))),$(2))),$(2))

Upvotes: 1

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