Description

$prefixpath c:\some\path\somewhere
is just a shortcut for
  $setenv PATH c:\some\path\somewhere;%sysenv.PATH%
that prevents the overflow of short strings
N.B. the environment variable name used in %sysenv.name% is case-sensitive

uses $prefixpath
     %sysenv.name%
%sysenv.xx% will just truncate to 255

this may overflow and give an error

Small Model of Type : GAMS

Category : GAMS Test library

Main file : sysenv01.gms

$title 'Tests for path and system environment strings' (SYSENV01,SEQ=219)

$ondollar
$set pathsep :
$if NOT %system.filesys% == UNIX $set pathsep ;

*   $prefixpath c:\some\path\somewhere
* is just a shortcut for
*   $setenv PATH c:\some\path\somewhere;%sysenv.PATH%
* that prevents the overflow of short strings
* N.B. the environment variable name used in %sysenv.name% is case-sensitive

* uses $prefixpath
*      %sysenv.name%
* %sysenv.xx% will just truncate to 255
$set oldpath "%sysenv.PATH%"
$set prefix this is a prefix
$if NOT errorfree $exit

* this may overflow and give an error
$set newpath "%prefix%%pathsep%%oldpath%"
$if NOT errorfree $clearerror
$prefixpath %prefix%
$set path "%sysenv.PATH%"
$if NOT errorfree $exit

display "path    =", "%path%";
display "newpath =", "%newpath%";

$if NOT "%path%" == "%newpath%" $error prefix path is messed up