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How To Add Library Paths to the ./configure Command

Ubuntu 19

When compiling software from source, the ./configure command plays a crucial role in preparing the software to be built on your specific system. It checks for dependencies, ensures the right libraries are in place, and sets up makefiles. However, sometimes the libraries you need aren’t in the standard locations that ./configure checks. In such cases, you need to add library paths to the ./configure command. This article will guide you through this process.

Quick Answer

To add library paths to the ./configure command, you can set the LDFLAGS and CPPFLAGS environment variables with the appropriate paths. Use the -L option for library search paths and the -I option for include file directories. Make sure to avoid subdirectories under library paths if they cause issues.

Understanding the ./configure Command

Before we delve into adding library paths, it’s important to understand what the ./configure command does. This command is a shell script generated by the Autotools suite. It’s used to detect system features, such as the presence of libraries, header files, and functions. It also checks for necessary tools and their versions. The ./configure command creates a tailored Makefile for your system, which is then used by the make command to build the software.

The Role of LDFLAGS and CPPFLAGS

To add library paths and include files to the ./configure command, we use the LDFLAGS and CPPFLAGS environment variables.

  • LDFLAGS is used to specify linker flags, such as library search paths (-L).
  • CPPFLAGS is used for the C Preprocessor, and it’s where you specify include file directories (-I).

Adding Library Paths

Here’s how to set these variables:

Set LDFLAGS and CPPFLAGS separately:

export CPPFLAGS="-I/home/foo/sw/include/"
export LDFLAGS="-L/home/foo/sw/lib/"
./configure

In this example, -I and -L are options that specify the directory for the include files and the libraries, respectively. The export command sets the environment variable for the duration of the current session.

Set LDFLAGS and CPPFLAGS in a single command:

env CPPFLAGS="-I/home/foo/sw/include/" LDFLAGS="-L/home/foo/sw/lib/" ./configure

The env command allows you to set environment variables for the duration of a single command, in this case, ./configure.

Use multiple entries in LDFLAGS:

export LDFLAGS="-L/home/foo/sw/lib/ -L/home/foo/bar/lib/"
./configure

If you have libraries in multiple locations, you can specify all of them in LDFLAGS.

Common Pitfalls

It’s important to note that if you have subdirectories under /home/foo/sw/lib/, you may encounter a “lib not found” error. In such cases, it’s recommended to avoid using subdirectories and place your library directly in /home/foo/sw/lib/.

Conclusion

In summary, to add library paths and include files to the ./configure command, you can set the LDFLAGS and CPPFLAGS environment variables with the appropriate paths. Make sure to use the correct syntax and avoid subdirectories under library paths if they cause issues. This will ensure that ./configure can find all the necessary libraries and dependencies, allowing your software to compile correctly.

For more information on the ./configure command and the Autotools suite, you can refer to the GNU Autoconf documentation.

Why do I need to add library paths to the `./configure` command?

You need to add library paths to the ./configure command when the libraries you require are not in the standard locations that ./configure checks. By specifying the library paths, you ensure that ./configure can find and link the necessary libraries during the software compilation process.

How do I know which library paths to add?

You can determine the library paths to add by checking the documentation or the installation instructions of the software you are compiling from source. Typically, the documentation will specify the required libraries and their installation paths. You can also use commands like ldconfig -p or pkg-config --libs to find the paths of installed libraries on your system.

Can I add multiple library paths to the `LDFLAGS` variable?

Yes, you can add multiple library paths to the LDFLAGS variable by separating them with spaces. For example, LDFLAGS="-L/path/to/lib1/ -L/path/to/lib2/". This allows you to specify multiple directories where ./configure should search for libraries.

Can I specify multiple include file directories using the `CPPFLAGS` variable?

Yes, you can specify multiple include file directories using the CPPFLAGS variable by separating them with spaces. For example, CPPFLAGS="-I/path/to/include1/ -I/path/to/include2/". This allows you to specify multiple directories where ./configure should search for header files.

What should I do if I encounter a “lib not found” error?

If you encounter a "lib not found" error, it may indicate that the library you specified in the library path (-L) is not present in the specified directory. Double-check the path and make sure the library file is located there. If you have subdirectories under the library path, try placing the library directly in the specified directory to avoid any issues.

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