Scons - a build system in Python - building hello world
Archive - Originally posted on "The Horse's Mouth" - 2016-10-29 21:23:46 - Graham EllisScons ...
It's a build system!!
Like Make (if you're familiar with that) or Ant (if you know that!)
The initial problem being solved ...
You have a whole lot of different development files (source files, libraries, manual text, configuration, etc) and a whole load of steps you use to convert those files - perhaps via intermediates - to executable programs, webpages, etc.. An you have a whole load of tests you may want to run too. A batch file doesn't 'cut' it as shell really doesn't have the facilities, and there's a lot of checking that needs to be done to see whether steps of a very long build actually need to be done every time when you've only changed one element of the source.
Add to the above the need to build for different operating systems, for different environments, to packages the results for distribution and add a signature to them, and to work with source code control systems ... and there's you problem.
Features (text from the Scons site - they know what they want to sell!!)
• Configuration files are Python scripts--use the power of a real programming language to solve build problems.
• Reliable, automatic dependency analysis built-in for C, C++ and Fortran--no more "make depend" or "make clean" to get all of the dependencies. Dependency analysis is easily extensible through user-defined dependency Scanners for other languages or file types.
• Built-in support for C, C++, D, Java, Fortran, Yacc, Lex, Qt and SWIG, and building TeX and LaTeX documents. Easily extensible through user-defined Builders for other languages or file types.
• Building from central repositories of source code and/or pre-built targets.
• Built-in support for fetching source files from SCCS, RCS, CVS, BitKeeper and Perforce.
• Built-in support for Microsoft Visual Studio .NET and past Visual Studio versions, including generation of .dsp, .dsw, .sln and .vcproj files.
• Reliable detection of build changes using MD5 signatures; optional, configurable support for traditional timestamps.
• Improved support for parallel builds--like make -j but keeps N jobs running simultaneously regardless of directory hierarchy.
• Integrated Autoconf-like support for finding #include files, libraries, functions and typedefs.
• Global view of all dependencies--no more multiple build passes or reordering targets to build everything.
• Ability to share built files in a cache to speed up multiple builds--like ccache but for any type of target file, not just C/C++ compilation.
• Designed from the ground up for cross-platform builds, and known to work on Linux, other POSIX systems (including AIX, *BSD systems, HP/UX, IRIX and Solaris), Windows NT, Mac OS X, and OS/2
Installation (lets do it easy!)
Download, unpack the .tar.gz and
sudo python setup.py installThe latest version (2.5.0) requires Python 2.7. "As we move towards Python 3" they say! - October 2016
http://scons.org/documentation.html
Hello Scons world
Building a "do nothing really" SConstruct file:
WomanWithCat:q3 grahamellis$ vi SConstruct
WomanWithCat:q3 grahamellis$ cat SConstruct
# This is my Scons build file demo
print "hello world"
WomanWithCat:q3 grahamellis$ scons
scons: Reading SConscript files ...
hello world
scons: done reading SConscript files.
scons: Building targets ...
scons: `.' is up to date.
scons: done building targets.
WomanWithCat:q3 grahamellis$ ls
SConstruct
WomanWithCat:q3 grahamellis$ Building a "make a program called hello from hello.c" construct file
WomanWithCat:q3 grahamellis$ cat hello.c
#include <stdio.h>
int main() {
printf("Hello World!\n");
}
WomanWithCat:q3 grahamellis$ cat scons_1
Program('hello.c')
WomanWithCat:q3 grahamellis$ scons -f scons_1
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
gcc -o hello.o -c hello.c
scons: done building targets.
WomanWithCat:q3 grahamellis$ scons -f scons_1
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
scons: `.' is up to date.
scons: done building targets.
WomanWithCat:q3 grahamellis$ ls
SConstruct hello hello.c hello.o scons_1
WomanWithCat:q3 grahamellis$ ./hello
Hello World!Building a program with multiple sources
WomanWithCat:q3 grahamellis$ cat scons_2
result = "mealorder"
Program(result,['today.c','meals.c','snacks.c'])
WomanWithCat:q3 grahamellis$
WomanWithCat:q3 grahamellis$ cat today.c
#include <stdio.h>
#include "yum.h"
int main() {
printf("Rise and shine\n");
breakfast();
morning_coffee();
lunch();
afternoon_tea();
dinner();
supper();
printf("Time for a kip\n");
}
WomanWithCat:q3 grahamellis$ cat yum.h
void breakfast();
void morning_coffee();
void lunch();
void afternoon_tea();
void dinner();
void supper();
WomanWithCat:q3 grahamellis$ cat meals.c
#include <stdio.h>
void breakfast(){
printf("breakfast\n");
}
void lunch(){
printf("lunch\n");
}
void dinner(){
printf("dinner\n");
}
WomanWithCat:q3 grahamellis$ cat snacks.c
#include <stdio.h>
void morning_coffee(){
printf("morning coffee\n");
}
void supper(){
printf("nightcap\n");
}
void afternoon_tea(){
printf("afternoon tea\n");
}
WomanWithCat:q3 grahamellis$
WomanWithCat:q3 grahamellis$ scons -f scons_2
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
gcc -o today.o -c today.c
gcc -o meals.o -c meals.c
gcc -o snacks.o -c snacks.c
gcc -o mealorder today.o meals.o snacks.o
scons: done building targets.
WomanWithCat:q3 grahamellis$ scons -f scons_2
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
scons: `.' is up to date.
scons: done building targets.
WomanWithCat:q3 grahamellis$ vi today.c
WomanWithCat:q3 grahamellis$ scons -f scons_2
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
gcc -o today.o -c today.c
gcc -o mealorder today.o meals.o snacks.o
scons: done building targets.
WomanWithCat:q3 grahamellis$ ./mealorder
Rise and shine
breakfast
morning coffee
morning coffee
lunch
afternoon tea
afternoon tea
dinner
nightcap
Time for a kip
WomanWithCat:q3 grahamellis$
And here ends what we cover on this day ;-)