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### IDE versus command line

On the Dos (DJGPP) and Linux platforms, you can use RHIDE for GNU Pascal; check the subdirectories of your DJGPP distribution.

Unfortunately, there is no IDE which would run on all platforms. We are working on it, but this will take some time. Please be patient - or offer your help!

Without an IDE, the GNU Pascal Compiler, GPC, is called about like the command-line version of the Borland Pascal Compiler, BPC. Edit your source file(s) with your favorite ASCII editor, then call GNU Pascal with a command line like

    C:\GNU-PAS> gpc hello.pas -o hello.exe

on your Dos or OS/2 box or

    myhost:/home/joe/gnu-pascal> gpc hello.pas -o hello

on your Unix (or Unix-compatible) system.

Don't omit the `.pas` suffix: GPC is a common interface for a Pascal compiler, a C, ObjC and C++ compiler, an assembler, a linker, and perhaps an Ada and a FORTRAN compiler. From the extension of your source file GPC figures out which compiler to run. GPC recognizes Pascal sources by the extension `.pas`, `.p`, `.pp` or `.dpr`.

The `-o` is a command line option which tells GPC how the executable has to be named. If not given, the executable will be called `a.out` (Unix) or `a.exe` (Dos). However, you can use the `--executable-file-name` to tell GPC to always call the executable like the source (with the extension removed under Unix and changed to `.exe` under Dos).

Note that GPC is case-sensitive concerning file names and options, so it will not work if you type

    C:\GNU-PAS> GPC HELLO.PAS -O HELLO.EXE

GPC is a very quiet compiler and doesn't print anything on the screen unless you request it or there is an error. If you want to see what is going on, invoke GPC with additional options:

    -Q            "don't be quiet"  (or: Quassel-Modus in German)

(with capital `Q`!) means that GPC prints out the names of procedures and functions it processes, and

    --verbose

or abbreviated

    -v

means that GPC informs you about the stages of compilation, i.e. preprocessing, compiling, assembling, and linking.

One example (this time for OS/2):

    [C:\GNU-Pascal] gpc --verbose -Q hello.pas

Throughout this chapter, we will tell you about a lot of command-line switches. They are all invoked this way.

After compilation, there will be an executable `hello` file in the current directory. (`hello.exe` on Dos or OS/2.) Just run it and enjoy. If you're new to Unix, please note that the current directory is not on the PATH in most installations, so you might have to run your program as `./hello`. This also helps to avoid name conflicts with other programs. Such conflicts are especially common with the program name `test` which happens to be a standard utility under Unix that does not print any output. If you call your program `test.pas`, compile it, and then invoke `test`, you will usually not run your program, but the utility which leads to mysterious problems. So, invoke your program as `./test` or, better yet, avoid the name `test` for your programs.

If there are compilation errors, GNU Pascal will not stop compilation after the first one - as Borland Pascal does - but try to catch all errors in one compilation. If you get more error messages than your screen can hold, you can catch them in a file (e.g. `gpc.out`) or pipe them to a program like `more` in the following way:

    gpc hello.pas 2> gpc.out

This works with OS/2 and any bash-like shell under Unix; for Dos you must get a replacement for `command.com` which supports this kind of redirection, or use the `redir` utility (see also the DJGPP FAQ, DJGPP FAQ.):

    C:\GNU-PAS> redir -eo gpc hello.pas -o hello.exe | more

You can also use Borland's IDE for GNU Pascal on the Dos platform: Install the GNU Pascal Compiler in the Tools menu (via Options/Tools).

    Name:       GNU Pascal
    Path:       gpc
    Arguments:  $SAVE ALL --executable-file-name $NAME($EDNAME).pas
    HotKey:     Shift+F9

Note once more that GPC is case-sensitive, so it is important to specify `.pas` instead of the `.PAS` Borland Pascal would append otherwise!

You can include more command-line arguments to GNU Pascal (e.g. `--automake`; see below) as you will learn more about them.

Since Borland Pascal will try to recompile your program if you use its `Run` menu function, you will need another tool to run your program:

    Name:       Run Program
    Path:       command.com
    Arguments:  /c $NAME($EDNAME)
    HotKey:     Shift+F10