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This tool allows to run pascal programs as scripts under Linux, BSD, macOS and Windows. For example:

#!/usr/bin/env instantfpc
  writeln('Hello fpc user');

Save the file as hello.pas, set the permission to execute and run it:

chmod a+x hello.pas
Hello fpc user


  • The first line is called shebang and is stripped from the source before passing it to the compiler.
  • The line 'program hello;' is optional in FPC. Because instantfpc passes the -o option to the compiler the line is ignored, so you can omit it.

Of course you can pass parameters to your script:

#!/usr/bin/env instantfpc
  i: Integer;
  for i:=0 to ParamCount do writeln(ParamStr(i));

Save the file as params.pas, set the permission to execute and run it:

chmod a+x params.pas
./params.pas A B

It gives output like:



No need to download: instantfpc is part of the FPC 2.6+ sources under utils/instantfpc and installed by default.

Old versions

For fpc 2.5.1 and above: It is in the fpc sources:

svn co instantfpc

For fpc 2.4.4 and 2.4.5:

svn co instantfpc


Note: It is already installed when using fpc 2.5.1 and above. Windows users have to put the instantfpc.exe into a directory of their PATH.

  1. Compile the instantfpc.lpi with Lazarus or lazbuild. Or compile directly with fpc instantfpc.pas.
  2. Put the executable into PATH, for example /usr/bin:
sudo cp instantfpc /usr/bin/

How it works

It uses a cache directory to compile. Default is $HOME/.cache/instantfpc. If HOME is not set it gives an error. You can override the directory by setting the environment variable INSTANTFPCCACHE. It compares the source with the stored file in cache and if it differs compiles the source, given the parameters in the shebang line (the first line of the script after #!). After successful compile it executes the program. If compilation fails it writes the fpc output to stdout.

Parameters for instantfpc

  • -h: Print help and exit
  • -v: Print current version and exit
  • --get-cache: Print current cache directory and exit
  • --set-cache=<directory>: Set cache directory
  • -B: always compile even if cache is valid.
  • --compiler=<path to compiler> use this compiler. By default fpc is searched in PATH.
  • --skip-run: Do not execute the program. Useful to test if script compiles. Best combined with -B.
  • --: Read the program source from standard input. Note that the compiled program has no input then.
  • Environment variable INSTANTFPCCACHE: Set cache directory. The --get-cache can override this.
  • Environment variable INSTANTFPCOPTIONS: Options to pass to the compiler. Passed before the command line parameters.

Passing parameters to the compiler

Compiler parameters can be passed in the shebang line. Note: You can not use the 'env' command.

#!/usr/bin/instantfpc -O1 -Ci

And/Or you can put compiler options in the environment variable INSTANTFPCOPTIONS:

export INSTANTFPCOPTIONS="-Fu~/lazarus/components/codetools/units/x86_64-linux/"
uses FileProcs; // unit FileProcs is in codetools


The following example script delivers the (unintelligible!) numeronym of a string (e.g. i18n for internationalization) that may be provided either as a parameter or, if missing, be entered by the user:

#!/usr/bin/env instantfpc
  theWord: String;
  if ParamStr(1) = '' then
    write('Please enter the word to be numeronymized: ');
    theWord := ParamStr(1);
  if length(theWord) > 2 then
    writeln(theWord[1] + IntToStr(length(theWord)-2) + theWord[length(theWord)])

The following shows how you don't even need to have a source file to use instantfpc:

echo "begin writeln('hello, world!') end." | ./instantfpc --

Using with Lazarus

Since Lazarus 0.9.31 the IDE ignores the shebang line. You get all the normal code features.

Install the IDE package instantfpclaz, which comes with Lazarus. This will add a new project item to create instantfpc programs, for example under File / New / Project / InstantFPC program.

Compile in Lazarus

How to convert a Lazarus project to compile it with instantfpc:


  • Lazarus project main source file is the instantfpc program


  • Go to Project Options / Compiler Options / Compilation
  • Disable all Call on checks for Compiler
  • Set in Execute before the Command to:
instantfpc --skip-run -B -gl "-Fu$(ProjUnitPath)" $Name($(ProjFile))
  • Enable checkboxes to scan make and fpc


  • The -gl will tell FPC to compile with debugging information
  • The --skip-run -B compiles without executing
  • See IDE Macros

Debug with Lazarus

How to convert a Lazarus project to debug an instantfpc program:


  • The above Compile in Lazarus


  • Go to Run / Run parameters
  • Set Local / Host application to
  • Set Working Directory to

Use as Pascal script without an .lpi file

Open the script in the source editor. Then click in menu Run / Configure Build and Run.

  • Page Options:
    • On build project execute the Build File command instead: Enable this if you like to compile the script on Ctrl+F9.
    • On run project execute the Run File command instead: Enable this if you like to execute the script on F9. Note: instantfpc automatically compiles if the file has changed.
  • Page Build:
    • 'Build Command: /path/to/instantfpc --skip-run -B -gl $(EdFile)
    • Scan for FPC messages: enable
  • Page Run:
    • 'Build Command: /path/to/instantfpc -gl $(EdFile)

Click Ok. You should see something like this:

{%BuildCommand /path/to/instantfpc --skip-run -B -gl $(EdFile)}
{%RunCommand /path/to/instantfpc -gl $(EdFile)}

Using in Apache

This is how to use instantfpc in Apache Webserver. Instantfpc needs the cache directory, which must be writable by the account of Apache. Let's say Apache is running under user www-data, group www-data (Redhat, Fedora: apache.apache, see apache config for User and Group).

mkdir /var/apacheinstantfpc
chown www-data.www-data /var/apacheinstantfpc

Pass an environment variable to cgi scripts by adding the following line to the Apache configs:

SetEnv INSTANTFPCCACHE /var/apacheinstantfpc

Security advice: Although the apache user must have full access to the cache directory, make sure the directory is not available from outside (e.g. do not put it under /var/www). It may contain old scripts. And like any other type of scripts: Check all input for attacks.

Optimization note: The instantfpc cache uses one file per script name. Do not use the same script name twice, otherwise it will be compiled many times. You can create multiple cache directories. Each <directory> and <virtualhost> section can define their own environment variables, and therefore you can setup one cache directory for each.

Apache example showing env

Configure a directory to execute cgi scripts. For example:

 ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/
 <Directory "/usr/lib/cgi-bin">
   AllowOverride None
   Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
   Order allow,deny
   Allow from all
   SetEnv INSTANTFPCCACHE /var/apacheinstantfpc
   # You can put fpc options into /etc/fpc.cfg or here:
   #SetEnv INSTANTFPCOPTIONS -Fu/path/to/somevar/ppufiles
   # If this is root directory, you might have to set:
   #Require all granted

If your apache has not yet enabled the cgi module:

a2enmod cgi

Put the following script into /usr/lib/cgi-bin/showenv.pas:

{$mode objfpc}{$H+}
uses  SysUtils;
var  i: Integer;
  writeln('Content-type: text/html');
  for i:=0 to Paramcount do
    writeln('Param ',i,' ',ParamStr(i),'<br>');
  for i:=1 to GetEnvironmentVariableCount do
    writeln('Env ',GetEnvironmentString(i),'<br>');

Bugs / ToDos / Limitations

  • Changes to the compiler or installed units are not checked. If you install a new compiler you should clean the cache (e.g. delete the directory ~/.cache/instantfpc).
  • Under Windows only the first parameter is passed to the script.
  • With instantfpc versions less than 1.3 you can not compile in parallel. The compiler creates hidden files like 'link.res' while compiling. Since 1.3 instantfpc uses temporary directories for compiling.
  • The cache uses the file name without the path. So you cannot execute two scripts in parallel of the same name. Every run time the script will be compiled.


The following trick works using the bash shell. Put the program into a file

// 2>/dev/null; fpc fpc_script.pp &> build.log && exec ./fpc_script "$@" || cat build.log; exit
  writeln(' no one knows how this is a trick or offers any advantage at all ');