# Using the Command Line

Recall that earlier the manual discussed how to use an existing toolchain tarball that had been installed into the default installation directory, `/opt/poky/&DISTRO;`, which is outside of the Build Directory (see the section "Using a Cross-Toolchain Tarball)". And, that sourcing your architecture-specific environment setup script initializes a suitable cross-toolchain development environment.

During this setup, locations for the compiler, QEMU scripts, QEMU binary, a special version of `pkgconfig` and other useful utilities are added to the `PATH` variable. Also, variables to assist `pkgconfig` and `autotools` are also defined so that, for example, `configure.sh` can find pre-generated test results for tests that need target hardware on which to run. You can see the "Setting Up the Cross-Development Environment" section for the list of cross-toolchain environment variables established by the script.

Collectively, these conditions allow you to easily use the toolchain outside of the OpenEmbedded build environment on both Autotools-based projects and Makefile-based projects. This chapter provides information for both these types of projects.

## Autotools-Based Projects

Once you have a suitable cross-toolchain installed, it is very easy to develop a project outside of the OpenEmbedded build system. This section presents a simple "Helloworld" example that shows how to set up, compile, and run the project.

### Creating and Running a Project Based on GNU Autotools

Follow these steps to create a simple Autotools-based project:

1. Create your directory: Create a clean directory for your project and then make that directory your working location:

            $ mkdir $HOME/helloworld
            $ cd $HOME/helloworld

2. Populate the directory: Create `hello.c`, `Makefile.am`, and `configure.in` files as follows:

   - For `hello.c`, include these lines:

              #include <stdio.h>

              main()
                 {
                    printf("Hello World!\n");
                 }

   - For `Makefile.am`, include these lines:

              bin_PROGRAMS = hello
              hello_SOURCES = hello.c

   - For `configure.in`, include these lines:

              AC_INIT(hello.c)
              AM_INIT_AUTOMAKE(hello,0.1)
              AC_PROG_CC
              AC_PROG_INSTALL
              AC_OUTPUT(Makefile)

3. Source the cross-toolchain environment setup file: Installation of the cross-toolchain creates a cross-toolchain environment setup script in the directory that the ADT was installed. Before you can use the tools to develop your project, you must source this setup script. The script begins with the string "environment-setup" and contains the machine architecture, which is followed by the string "poky-linux". Here is an example that sources a script from the default ADT installation directory that uses the 32-bit Intel x86 Architecture and the &DISTRO_NAME; Yocto Project release:

            $ source /opt/poky/&DISTRO;/environment-setup-i586-poky-linux

4. Generate the local aclocal.m4 files and create the configure script: The following GNU Autotools generate the local `aclocal.m4` files and create the configure script:

            $ aclocal
            $ autoconf

5. Generate files needed by GNU coding standards: GNU coding standards require certain files in order for the project to be compliant. This command creates those files:

            $ touch NEWS README AUTHORS ChangeLog

6. Generate the configure file: This command generates the `configure`:

            $ automake -a

7. Cross-compile the project: This command compiles the project using the cross-compiler. The `CONFIGURE_FLAGS` environment variable provides the minimal arguments for GNU configure:

            $ ./configure ${CONFIGURE_FLAGS}

8. Make and install the project: These two commands generate and install the project into the destination directory:

            $ make
            $ make install DESTDIR=./tmp

9. Verify the installation: This command is a simple way to verify the installation of your project. Running the command prints the architecture on which the binary file can run. This architecture should be the same architecture that the installed cross-toolchain supports.

            $ file ./tmp/usr/local/bin/hello

10. Execute your project: To execute the project in the shell, simply enter the name. You could also copy the binary to the actual target hardware and run the project there as well:

             $ ./hello

    As expected, the project displays the "Hello World!" message.

### Passing Host Options

For an Autotools-based project, you can use the cross-toolchain by just passing the appropriate host option to `configure.sh`. The host option you use is derived from the name of the environment setup script found in the directory in which you installed the cross-toolchain. For example, the host option for an ARM-based target that uses the GNU EABI is `armv5te-poky-linux-gnueabi`. You will notice that the name of the script is `environment-setup-armv5te-poky-linux-gnueabi`. Thus, the following command works to update your project and rebuild it using the appropriate cross-toolchain tools:

         $ ./configure --host=armv5te-poky-linux-gnueabi \
            --with-libtool-sysroot=sysroot_dir

If the `configure` script results in problems recognizing the `--with-libtool-sysroot=`sysroot-dir option, regenerate the script to enable the support by doing the following and then run the script again:

         $ libtoolize --automake
         $ aclocal -I ${OECORE_NATIVE_SYSROOT}/usr/share/aclocal \
            [-I dir_containing_your_project-specific_m4_macros]
         $ autoconf
         $ autoheader
         $ automake -a

## Makefile-Based Projects

For Makefile-based projects, the cross-toolchain environment variables established by running the cross-toolchain environment setup script are subject to general `make` rules.

To illustrate this, consider the following four cross-toolchain environment variables:

         CC=i586-poky-linux-gcc -m32 -march=i586 --sysroot=/opt/poky/1.8/sysroots/i586-poky-linux
         LD=i586-poky-linux-ld --sysroot=/opt/poky/1.8/sysroots/i586-poky-linux
         CFLAGS=-O2 -pipe -g -feliminate-unused-debug-types
         CXXFLAGS=-O2 -pipe -g -feliminate-unused-debug-types

Now, consider the following three cases:

- Case 1 - No Variables Set in the `Makefile`: Because these variables are not specifically set in the `Makefile`, the variables retain their values based on the environment.

- Case 2 - Variables Set in the `Makefile`: Specifically setting variables in the `Makefile` during the build results in the environment settings of the variables being overwritten.

- Case 3 - Variables Set when the `Makefile` is Executed from the Command Line: Executing the `Makefile` from the command line results in the variables being overwritten with command-line content regardless of what is being set in the `Makefile`. In this case, environment variables are not considered unless you use the "-e" flag during the build:

           $ make -e file

  If you use this flag, then the environment values of the variables override any variables specifically set in the `Makefile`.

For the list of variables set up by the cross-toolchain environment setup script, see the "Setting Up the Cross-Development Environment" section.