How to use the command 'libtool' (with examples)

Libtool is a versatile and powerful command-line utility designed to simplify the process of consistently using shared libraries across different platforms. It provides a portable and coherent interface, masking the complexities that come with creating, linking, and managing shared libraries. Its primary purpose is to facilitate the development of library support scripts that can work seamlessly, whether the libraries are shared or static, across diverse environments without additional steps or configurations.

Use case 1: Compile a source file into a libtool object

Code:

libtool --mode=compile gcc -c path/to/source.c -o path/to/source.lo

Motivation: Compiling a source file into a libtool object is an essential step in the process of building a library or an executable. The libtool object files have a standard .lo extension, differentiating them from regular object files. This intermediate step enables compatibility and ensures that the object files can be linked into libraries or executables later while maintaining optimal portable library handling.

Explanation:

• --mode=compile: Specifies that the operation is to compile source code.
• gcc: The compiler being used for the compilation, standing for GNU Compiler Collection.
• -c: An option for the compiler to compile only, generating object files but not linking.
• path/to/source.c: The path to the source C file that needs to be compiled.
• -o path/to/source.lo: Specifies the output file name with a .lo extension, a libtool object file.

Example Output: Compiling source.c… Generating source.lo done.

Use case 2: Create a library or an executable

Code:

libtool --mode=link gcc -o path/to/library.lo path/to/source.lo

Motivation: Creating a library or an executable is the next logical step after compiling source files into object files. This process involves linking these object files. By using libtool, you ensure that the linking process is handled in a way that maintains cross-platform compatibility and automatically deals with dependencies and shared libraries.

Explanation:

• --mode=link: Instructs libtool to link object files.
• gcc: The linking compiler.
• -o path/to/library.lo: Specifies the output file. The .lo extension indicates it’s a libtool library object.
• path/to/source.lo: Input object files that will be linked to form the library or executable.

Example Output: Linking files… Library linked as library.lo

Use case 3: Automatically set the library path

Code:

libtool --mode=execute gdb path/to/program

Motivation: Running and debugging programs that depend on libraries not yet installed system-wide requires a method to set up library paths correctly. With libtool --mode=execute, you can execute another program while ensuring it can find the libtool-generated programs and libraries, even if they haven’t been officially installed. This is particularly useful in development or testing phases.

Explanation:

• --mode=execute: Initializes an environment to run a specific program.
• gdb: The GNU Debugger, used here to run the program for debugging purposes.
• path/to/program: The location of the program that needs to be executed or tested.

Example Output: Starting debugger… Program executed successfully with temporary library paths set.

Use case 4: Install a shared library

Code:

libtool --mode=install cp path/to/library.la path/to/installation_directory

Motivation: Installing a shared library is a critical part of deploying software that others will use. By installing the library properly, you ensure that it’s available to other programs or users on the system. The libtool-generated .la files provide additional metadata about the libraries, enhancing manageability, especially in larger projects.

Explanation:

• --mode=install: Specifies the intent to install a file.
• cp: The copy command, used to move files from one location to another.
• path/to/library.la: Source library file to install.
• path/to/installation_directory: Destination directory where the library will be placed.

Example Output: Copying library.la to /installation_directory… Library installed successfully.

Use case 5: Complete the installation of libtool libraries

Code:

libtool --mode=finish path/to/installation_dir

Motivation: Once libraries have been copied to their intended location, finishing the installation is often necessary to re-establish correct paths or permissions. This command makes certain that any final modifications or configurations are appropriately applied, securing seamless subsequent usages of the libraries.

Explanation:

• --mode=finish: Concludes the installation process, finalizing any outstanding tasks.
• path/to/installation_dir: Directory wherein the libtool libraries were installed, needing completion.

Example Output: Finalizing library installation in /installation_dir… Installation complete.

Use case 6: Delete installed libraries or executables

Code:

libtool --mode=uninstall path/to/installed_library.la

Motivation: Occasionally, libraries or executables may need to be removed, whether due to updates, deprecations, or simple cleanup. This libtool feature ensures safe and correct deletion of libraries, catering to all associated components potentially scattered across the system.

Explanation:

• --mode=uninstall: Signals that the task is to remove an existing library or executable.
• path/to/installed_library.la: Path indicating the specific library file targeted for removal.

Example Output: Uninstalling library.la… Library successfully removed.

Use case 7: Delete uninstalled libraries or executables

Code:

libtool --mode=clean rm path/to/source.lo path/to/library.la

Motivation: During development, numerous temporary or unnecessary files may accumulate. Cleaning up these additional libtool files that aren’t fully installed but linger in the build environment is crucial for maintaining a tidy workspace and avoiding potential linking or compiling issues.

Explanation:

• --mode=clean: Designates the action to clean or remove uninstalled items.
• rm: Command to remove files.
• path/to/source.lo path/to/library.la: Paths to files marked for deletion.

Example Output: Removing source.lo and library.la… Temporary files deleted successfully.

Conclusion

Libtool provides an essential service in managing the complexities of working with shared libraries across different systems and platforms. Whether you are compiling, linking, executing, installing, or cleaning up, libtool streamlines the processes, ensuring cross-platform portability and reliability in library management tasks. Each of the use cases covered showcases libtool’s versatility in handling various stages of library lifecycle maintenance.