A GNU Fortran installation includes a modified version of the gcc
command.
In a non-Fortran installation, gcc recognizes C, C++,
and Objective-C source files.
In a GNU Fortran installation, gcc also recognizes Fortran source
files and accepts Fortran-specific command-line options, plus some
command-line options that are designed to cater to Fortran users
but apply to other languages as well.
See Compile C; C++; Objective-C; Ada; Fortran; or Java,
for information on the way different languages are handled
by the GNU CC compiler (gcc).
Also provided as part of GNU Fortran is the g77 command.
The g77 command is designed to make compiling and linking Fortran
programs somewhat easier than when using the gcc command for
these tasks.
It does this by analyzing the command line somewhat and changing it
appropriately before submitting it to the gcc command.
Use the -v option with g77
to see what is going on--the first line of output is the invocation
of the gcc command.