Passing additional variables from command line to make

command-line-argumentsgnumakefile

Can I pass variables to a GNU Makefile as command line arguments? In other words, I want to pass some arguments which will eventually become variables in the Makefile.

Best Answer

You have several options to set up variables from outside your makefile:

From environment - each environment variable is transformed into a makefile variable with the same name and value.

You may also want to set -e option (aka --environments-override) on, and your environment variables will override assignments made into makefile (unless these assignments themselves use the override directive . However, it's not recommended, and it's much better and flexible to use ?= assignment (the conditional variable assignment operator, it only has an effect if the variable is not yet defined):
```
FOO?=default_value_if_not_set_in_environment
```
Note that certain variables are not inherited from environment:
- MAKE is gotten from name of the script
- SHELL is either set within a makefile, or defaults to /bin/sh (rationale: commands are specified within the makefile, and they're shell-specific).
From command line - make can take variable assignments as part of his command line, mingled with targets:
```
make target FOO=bar
```
But then all assignments to FOO variable within the makefile will be ignored unless you use the override directive in assignment. (The effect is the same as with -e option for environment variables).
Exporting from the parent Make - if you call Make from a Makefile, you usually shouldn't explicitly write variable assignments like this:
```
# Don't do this!
target:
        $(MAKE) -C target CC=$(CC) CFLAGS=$(CFLAGS)
```
Instead, better solution might be to export these variables. Exporting a variable makes it into the environment of every shell invocation, and Make calls from these commands pick these environment variable as specified above.
```
# Do like this
CFLAGS=-g
export CFLAGS
target:
        $(MAKE) -C target
```
You can also export all variables by using export without arguments.

Related Solutions

Ruby – How to pass command line arguments to a rake task

You can specify formal arguments in rake by adding symbol arguments to the task call. For example:

require 'rake'

task :my_task, [:arg1, :arg2] do |t, args|
  puts "Args were: #{args} of class #{args.class}"
  puts "arg1 was: '#{args[:arg1]}' of class #{args[:arg1].class}"
  puts "arg2 was: '#{args[:arg2]}' of class #{args[:arg2].class}"
end

task :invoke_my_task do
  Rake.application.invoke_task("my_task[1, 2]")
end

# or if you prefer this syntax...
task :invoke_my_task_2 do
  Rake::Task[:my_task].invoke(3, 4)
end

# a task with prerequisites passes its 
# arguments to it prerequisites
task :with_prerequisite, [:arg1, :arg2] => :my_task #<- name of prerequisite task

# to specify default values, 
# we take advantage of args being a Rake::TaskArguments object
task :with_defaults, :arg1, :arg2 do |t, args|
  args.with_defaults(:arg1 => :default_1, :arg2 => :default_2)
  puts "Args with defaults were: #{args}"
end

Then, from the command line:

> rake my_task[1,false]
Args were: {:arg1=>"1", :arg2=>"false"} of class Rake::TaskArguments
arg1 was: '1' of class String
arg2 was: 'false' of class String

> rake "my_task[1, 2]"
Args were: {:arg1=>"1", :arg2=>"2"}

> rake invoke_my_task
Args were: {:arg1=>"1", :arg2=>"2"}

> rake invoke_my_task_2
Args were: {:arg1=>3, :arg2=>4}

> rake with_prerequisite[5,6]
Args were: {:arg1=>"5", :arg2=>"6"}

> rake with_defaults
Args with defaults were: {:arg1=>:default_1, :arg2=>:default_2}

> rake with_defaults['x','y']
Args with defaults were: {:arg1=>"x", :arg2=>"y"}

As demonstrated in the second example, if you want to use spaces, the quotes around the target name are necessary to keep the shell from splitting up the arguments at the space.

Looking at the code in rake.rb, it appears that rake does not parse task strings to extract arguments for prerequisites, so you can't do task :t1 => "dep[1,2]". The only way to specify different arguments for a prerequisite would be to invoke it explicitly within the dependent task action, as in :invoke_my_task and :invoke_my_task_2.

Note that some shells (like zsh) require you to escape the brackets: rake my_task\['arg1'\]

Python – How to read/process command line arguments

import sys

print("\n".join(sys.argv))

sys.argv is a list that contains all the arguments passed to the script on the command line. sys.argv[0] is the script name.

Basically,

import sys
print(sys.argv[1:])

Best Answer

Related Solutions

Ruby – How to pass command line arguments to a rake task

Python – How to read/process command line arguments

Related Topic