use environment variable if set otherwise use default value in makefile
I can do this:
MY_VAR:=$(myvar)
But what I want is to also define a value for MY_VAR that is used if the environment variable myvar isn't defined. Is this possible?
Something like:
# pseudo code
MY_VAR:=if not $(myvar) then someDefaultValue
bash makefile
asked Nov 19 '18 at 7:15
red888red888
4,48673887
add a comment |
I can do this:
MY_VAR:=$(myvar)
But what I want is to also define a value for MY_VAR that is used if the environment variable myvar isn't defined. Is this possible?
Something like:
# pseudo code
MY_VAR:=if not $(myvar) then someDefaultValue
bash makefile
asked Nov 19 '18 at 7:15
red888red888
4,48673887
add a comment |
I can do this:
MY_VAR:=$(myvar)
But what I want is to also define a value for MY_VAR that is used if the environment variable myvar isn't defined. Is this possible?
Something like:
# pseudo code
MY_VAR:=if not $(myvar) then someDefaultValue
bash makefile
asked Nov 19 '18 at 7:15
red888red888
4,48673887
I can do this:
MY_VAR:=$(myvar)
But what I want is to also define a value for MY_VAR that is used if the environment variable myvar isn't defined. Is this possible?
Something like:
# pseudo code
MY_VAR:=if not $(myvar) then someDefaultValue
bash makefile
bash makefile
asked Nov 19 '18 at 7:15
red888red888
4,48673887
asked Nov 19 '18 at 7:15
red888red888
4,48673887
asked Nov 19 '18 at 7:15
red888red888
4,48673887
asked Nov 19 '18 at 7:15
red888red888
4,48673887
asked Nov 19 '18 at 7:15
red888red888
4,48673887
4,48673887
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
Assuming make is GNU Make, all the environment variable settings inherited by make are automatically registered
as make variable settings. See 6.10 Variables from the Environment. So you can just write, e.g.
Makefile (1)
ifdef myvar
MYVAR := $(myvar)
else
MYVAR := default
endif
.PHONY: all
all:
echo $(MYVAR)
Which runs like:
$ make
echo default
default
when myvar is not defined in the environment; and when it is defined,
runs like:
$ export myvar=notDefault
$ make
echo notDefault
notDefault
And in case the environment variable and the make variable are the same - and why not? - it is simpler still.
Makefile (2)
MYVAR ?= default
.PHONY: all
all:
echo $(MYVAR)
See 6.5 Setting Variables
Then:
$ make
echo default
default
$ export MYVAR=notDefault
$ make
echo notDefault
notDefault
answered Nov 19 '18 at 8:40
Mike KinghanMike Kinghan
30.4k763112
coool i saw the question mark in makefiles before, didnt realize this is what it does
– red888
Nov 19 '18 at 15:32
add a comment |
you can try this code below.
MY_VAR=${HOSTNAME1}
if [ "$MY_VAR" = "" ]; then
MY_VAR="DEFAULT"
fi
answered Nov 19 '18 at 7:35
akdakd
92
This is a verbose, and slightly incorrect, restatement of the simple built-in shell notationMY_VAR=${HOSTNAME1:-DEFAULT}(the error is that==should properly be=unless you specifically tell Make to use Bash as theSHELL).
– tripleee
Nov 19 '18 at 8:38
edited, thanks for the correction
– akd
Nov 19 '18 at 9:31
add a comment |
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2 Answers
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active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
Assuming make is GNU Make, all the environment variable settings inherited by make are automatically registered
as make variable settings. See 6.10 Variables from the Environment. So you can just write, e.g.
Makefile (1)
ifdef myvar
MYVAR := $(myvar)
else
MYVAR := default
endif
.PHONY: all
all:
echo $(MYVAR)
Which runs like:
$ make
echo default
default
when myvar is not defined in the environment; and when it is defined,
runs like:
$ export myvar=notDefault
$ make
echo notDefault
notDefault
And in case the environment variable and the make variable are the same - and why not? - it is simpler still.
Makefile (2)
MYVAR ?= default
.PHONY: all
all:
echo $(MYVAR)
See 6.5 Setting Variables
Then:
$ make
echo default
default
$ export MYVAR=notDefault
$ make
echo notDefault
notDefault
answered Nov 19 '18 at 8:40
Mike KinghanMike Kinghan
30.4k763112
coool i saw the question mark in makefiles before, didnt realize this is what it does
– red888
Nov 19 '18 at 15:32
add a comment |
Assuming make is GNU Make, all the environment variable settings inherited by make are automatically registered
as make variable settings. See 6.10 Variables from the Environment. So you can just write, e.g.
Makefile (1)
ifdef myvar
MYVAR := $(myvar)
else
MYVAR := default
endif
.PHONY: all
all:
echo $(MYVAR)
Which runs like:
$ make
echo default
default
when myvar is not defined in the environment; and when it is defined,
runs like:
$ export myvar=notDefault
$ make
echo notDefault
notDefault
And in case the environment variable and the make variable are the same - and why not? - it is simpler still.
Makefile (2)
MYVAR ?= default
.PHONY: all
all:
echo $(MYVAR)
See 6.5 Setting Variables
Then:
$ make
echo default
default
$ export MYVAR=notDefault
$ make
echo notDefault
notDefault
answered Nov 19 '18 at 8:40
Mike KinghanMike Kinghan
30.4k763112
coool i saw the question mark in makefiles before, didnt realize this is what it does
– red888
Nov 19 '18 at 15:32
add a comment |
Assuming make is GNU Make, all the environment variable settings inherited by make are automatically registered
as make variable settings. See 6.10 Variables from the Environment. So you can just write, e.g.
Makefile (1)
ifdef myvar
MYVAR := $(myvar)
else
MYVAR := default
endif
.PHONY: all
all:
echo $(MYVAR)
Which runs like:
$ make
echo default
default
when myvar is not defined in the environment; and when it is defined,
runs like:
$ export myvar=notDefault
$ make
echo notDefault
notDefault
And in case the environment variable and the make variable are the same - and why not? - it is simpler still.
Makefile (2)
MYVAR ?= default
.PHONY: all
all:
echo $(MYVAR)
See 6.5 Setting Variables
Then:
$ make
echo default
default
$ export MYVAR=notDefault
$ make
echo notDefault
notDefault
answered Nov 19 '18 at 8:40
Mike KinghanMike Kinghan
30.4k763112
Assuming make is GNU Make, all the environment variable settings inherited by make are automatically registered
as make variable settings. See 6.10 Variables from the Environment. So you can just write, e.g.
Makefile (1)
ifdef myvar
MYVAR := $(myvar)
else
MYVAR := default
endif
.PHONY: all
all:
echo $(MYVAR)
Which runs like:
$ make
echo default
default
when myvar is not defined in the environment; and when it is defined,
runs like:
$ export myvar=notDefault
$ make
echo notDefault
notDefault
And in case the environment variable and the make variable are the same - and why not? - it is simpler still.
Makefile (2)
MYVAR ?= default
.PHONY: all
all:
echo $(MYVAR)
See 6.5 Setting Variables
Then:
$ make
echo default
default
$ export MYVAR=notDefault
$ make
echo notDefault
notDefault
answered Nov 19 '18 at 8:40
Mike KinghanMike Kinghan
30.4k763112
edited Nov 19 '18 at 8:56
answered Nov 19 '18 at 8:40
Mike KinghanMike Kinghan
30.4k763112
answered Nov 19 '18 at 8:40
Mike KinghanMike Kinghan
30.4k763112
answered Nov 19 '18 at 8:40
Mike KinghanMike Kinghan
30.4k763112
30.4k763112
coool i saw the question mark in makefiles before, didnt realize this is what it does
– red888
Nov 19 '18 at 15:32
add a comment |
coool i saw the question mark in makefiles before, didnt realize this is what it does
– red888
Nov 19 '18 at 15:32
coool i saw the question mark in makefiles before, didnt realize this is what it does
– red888
Nov 19 '18 at 15:32
coool i saw the question mark in makefiles before, didnt realize this is what it does
– red888
Nov 19 '18 at 15:32
add a comment |
you can try this code below.
MY_VAR=${HOSTNAME1}
if [ "$MY_VAR" = "" ]; then
MY_VAR="DEFAULT"
fi
answered Nov 19 '18 at 7:35
akdakd
92
This is a verbose, and slightly incorrect, restatement of the simple built-in shell notationMY_VAR=${HOSTNAME1:-DEFAULT}(the error is that==should properly be=unless you specifically tell Make to use Bash as theSHELL).
– tripleee
Nov 19 '18 at 8:38
edited, thanks for the correction
– akd
Nov 19 '18 at 9:31
add a comment |
you can try this code below.
MY_VAR=${HOSTNAME1}
if [ "$MY_VAR" = "" ]; then
MY_VAR="DEFAULT"
fi
answered Nov 19 '18 at 7:35
akdakd
92
This is a verbose, and slightly incorrect, restatement of the simple built-in shell notationMY_VAR=${HOSTNAME1:-DEFAULT}(the error is that==should properly be=unless you specifically tell Make to use Bash as theSHELL).
– tripleee
Nov 19 '18 at 8:38
edited, thanks for the correction
– akd
Nov 19 '18 at 9:31
add a comment |
you can try this code below.
MY_VAR=${HOSTNAME1}
if [ "$MY_VAR" = "" ]; then
MY_VAR="DEFAULT"
fi
answered Nov 19 '18 at 7:35
akdakd
92
you can try this code below.
MY_VAR=${HOSTNAME1}
if [ "$MY_VAR" = "" ]; then
MY_VAR="DEFAULT"
fi
answered Nov 19 '18 at 7:35
akdakd
92
edited Nov 19 '18 at 9:30
answered Nov 19 '18 at 7:35
akdakd
92
answered Nov 19 '18 at 7:35
akdakd
92
answered Nov 19 '18 at 7:35
akdakd
92
92
This is a verbose, and slightly incorrect, restatement of the simple built-in shell notationMY_VAR=${HOSTNAME1:-DEFAULT}(the error is that==should properly be=unless you specifically tell Make to use Bash as theSHELL).
– tripleee
Nov 19 '18 at 8:38
edited, thanks for the correction
– akd
Nov 19 '18 at 9:31
add a comment |
This is a verbose, and slightly incorrect, restatement of the simple built-in shell notationMY_VAR=${HOSTNAME1:-DEFAULT}(the error is that==should properly be=unless you specifically tell Make to use Bash as theSHELL).
– tripleee
Nov 19 '18 at 8:38
edited, thanks for the correction
– akd
Nov 19 '18 at 9:31
This is a verbose, and slightly incorrect, restatement of the simple built-in shell notation
MY_VAR=${HOSTNAME1:-DEFAULT} (the error is that == should properly be = unless you specifically tell Make to use Bash as the SHELL).– tripleee
Nov 19 '18 at 8:38
This is a verbose, and slightly incorrect, restatement of the simple built-in shell notation
MY_VAR=${HOSTNAME1:-DEFAULT} (the error is that == should properly be = unless you specifically tell Make to use Bash as the SHELL).– tripleee
Nov 19 '18 at 8:38
edited, thanks for the correction
– akd
Nov 19 '18 at 9:31
edited, thanks for the correction
– akd
Nov 19 '18 at 9:31
add a comment |
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