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1

I'm trying to run a Python snippet inside a Make target, but I'm having trouble trying to figure out how these things work in Make.

Here is my attempt so far:

define BROWSER_PYSCRIPT
import os, webbrowser, sys
try:
    from urllib import pathname2url
except:
    from urllib.request import pathname2url

webbrowser.open("file://" + pathname2url(os.path.abspath(sys.argv[1])))
endef
BROWSER := $(shell python -c '$(BROWSER_PYSCRIPT)')

I wanted to use $(BROWSER) in a target like:

docs:
    #.. compile docs
    $(BROWSER) docs/index.html

Is this really a bad idea?

share|improve this question

2 Answers 2

up vote 1 down vote accepted

Related: http://stackoverflow.com/q/649246/4937930

You cannot recall a multi-line variable as is in a single recipe, it rather gets expanded to multiple recipes and causes syntax error.

A possible workaround would be:

export BROWSER_PYSCRIPT
BROWSER := python -c "$$BROWSER_PYSCRIPT"

docs:
        #.. compile docs
        $(BROWSER) docs/index.html
share|improve this answer
    
yay, it works, thank you very much! :) so, I assume that export command turns it into a variable in the environment, and then we use shell expansion to get it later? could you explain at which point "$$BROWSER_PYSCRIPT" is evaluated? –  elias Aug 13 at 12:21
    
$$ is an escaped $ so it becomes $BROWSER_PYSCRIPT in $(BROWSER). Make leaves it untouched, just passes a recipe string python -c "$BROWSER_PYSCRIPT" docs/index.html as-is to $(SHELL) (usually /bin/sh), along with BROWSER_SCRIPT exported in the environment variables. –  yaegashi Aug 14 at 9:41
    
cool, neat trick! :) –  elias Aug 14 at 13:18
up vote 1 down vote

Yaegashi's approach will work, but it won't be easy to give it on-the-fly values. The 'export' command is evaluated while the Makefile is being parsed, and sets a shell environment variable to the recipe. Then the environment variable is evaluated during execution of the 'docs' recipe.

If your snippet needs to have any target-dependent variables filled in, I'd recommend an approach like this:

Quick Approach

If you just need to run a couple of one-liners, this pattern will work pretty well.

run_script = python -c \
"import time ;\
print 'Hello world!' ;\
print '%d + %d = %d' %($1,$2,$1+$2) ;\
print 'Running target \'%s\' at time %s' %('$3', time.ctime())"

test:
    $(call run_script,4,3,$@)

Fancy Approach

If you want to use weird characters and functions, for-loops, or other multi-line constructs, here's a fancy pattern that will work beautifully.

#--------------------------- Python Script Runner ----------------------------#

define \n


endef

escape_shellstring = \
$(subst `,\`,\
$(subst ",\",\
$(subst $$,\$$,\
$(subst \,\\,\
$1))))

escape_printf = \
$(subst \,\\,\
$(subst %,%%,\
$1))

create_string = \
$(subst $(\n),\n,\
$(call escape_shellstring,\
$(call escape_printf,\
$1)))

python_script = printf "$(call create_string,$($(1)))" | python

#------------------------------- User Scripts --------------------------------#

define my_script

def good_times():
    print "good times!"

import time
print 'Hello world!'
print '%d + %d = %d' %($2,$3,$2+$3)
print 'Runni`ng $$BEEF \ttarget \t\n\n"%s" at time %s' %('$4', time.ctime())
good_times()

endef

#--------------------------------- Recipes -----------------------------------#

test:
    $(call python_script,my_script,1,2,$@)
share|improve this answer
    
interesting, thanks! I did try to use parameterized macros, but found them a bit cumbersome. in my case, I will only use under targets, so the export trick is cleaner to me. thank you anyway! :) –  elias Aug 14 at 13:20

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