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This project is to test an idea by Kartik Agaram: using the shell as a substitute of a build system (i.e. make, cmake, jam, ...).

You can find his post here:

The key idea is to define a function older_then() that checks whether a file is older than its dependecies and use it to execute the instruction to re-build it only when needed.

I've stressed his idea a little bit and decided to use bash (his suggestion was to use the Bourne shell for the maximum compatibility).

Project structure

The assumption is that a project is stored in a directory structure similar to this (with possibly sub-dirs):

 (top dir)
      |-- src
      |-- doc
      |-- test
      |-- lib
      |-- ...

The top directory must contain 2 scripts:

  • with the global variables and common functions for the projects
  • bld.trg with the definition of the targets that can be built from the top directory.

all the other directories can contain a bld.trg that defines the target that can be built starting from that directory.

The top directory is also a good place to store the bld script itself if it's not in your PATH.

A target is a function whose name starts with an underscore. For example:

    _clean () {
       # Clean up commands here.

Command line options

To build a target, you invoke the bld script.

  Usage: bld [options] [targets ...]
  Version: "0.1.3-beta" (0x0001003B)
  Options: -h              this help
           -f              force rebuild
           -e              exit on error
           -l              list available targets
           -d dir          move to the specified directory before building
           -t file         load the specified target file (default: bld.trg)
           -D "VAR=VALUE"  set the variable VAR to VALUE
  Target defaults to 'all'

Assuming bld is in your path, the command:

    > bld clean

will execute the _clean function (assuming it's defined in your bld.trg script). You can specify more than one target. To build a target that is in another directory you can use the -d switch. For example:

    > bld -d test clean

will build the clean target as defined in the test directory.

Note that targets are just labels, they are not directly related to files.

    > bld -l

will provide the list of available targets.


  • bld [-d dir] [-f] [target ...] Builds the specified targets. If the -d flag is specified, the build is started in the specified directory as a new process.

  • bld_old targ f1 f2 ... Checks if the target file targ is older than its dependencoes f1, f2, ... This function is to be used as in the following example:

         bld_old myexe src1.c src2.c && {
           # recompile myexe
  • bld_cmd This is useful if you want the build script to emit the command that is to be executed. For example:

        bld_cmd gcc -c src.c

    will print on stderr the command before executing it

Pseudo target

Is sometimes desirable to have pseudotargets, i.e. targets that can be handled in a common way.

You can define the function _default() that will handle any unknown target.

An example of pseudo targets is provided in the test directory of the lorem Ipsum project (see next section)

The lorem Ipsum project

To provide a better example of how to use bld you can refer to the files in this repository.

The directory src contains the source files for a (fake) library that will be built in the lib directory.

The directory test contains the unit tests for the library. To ease the addition of new tests, the convention is that any C source file whose name starts with ut_* is a unit test and that any unit test itself is a program whose name starts with t_*

Building everything:

    > bld all

Checking if the liblorem.a library is recompiled properly

    > touch src/dolor.c
    > bld -d lib dolor


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