How do I modify the PATH environment variable when running an Inno Setup Installer?

Question

Inno Setup lets you set environment variables via the [Registry] sections (by setting registry key which correspond to environment variable)

However, sometimes you d

Answer 1

I want to thank everyone for their contributions to this question. I've incorporated about 95% of the code posted by Wojciech Mleczek into my app's installer. I do have some corrections to that code that may prove useful to others. My changes:

• Renamed formal argument Path to instlPath. Cuts down on multiple uses of "Path" in code (easier to read, IMO).

• When installing/uninstalling, add an existence check for an instlPath that ends with \;.

• During installation, don't double up ; in the current %PATH%.

• Handle missing or empty %PATH% during installation.

• During uninstall, make sure that a starting index of 0 is not passed to Delete().

Here's my updated version of EnvAddPath():

const EnvironmentKey = 'Environment';

procedure EnvAddPath(instlPath: string);
var
    Paths: string;
begin
    { Retrieve current path (use empty string if entry not exists) }
    if not RegQueryStringValue(HKEY_CURRENT_USER, EnvironmentKey, 'Path', Paths) then
        Paths := '';

    if Paths = '' then
        Paths := instlPath + ';'
    else
    begin
        { Skip if string already found in path }
        if Pos(';' + Uppercase(instlPath) + ';',  ';' + Uppercase(Paths) + ';') > 0 then exit;
        if Pos(';' + Uppercase(instlPath) + '\;', ';' + Uppercase(Paths) + ';') > 0 then exit;

        { Append App Install Path to the end of the path variable }
        Log(Format('Right(Paths, 1): [%s]', [Paths[length(Paths)]]));
        if Paths[length(Paths)] = ';' then
            Paths := Paths + instlPath + ';'  { don't double up ';' in env(PATH) }
        else
            Paths := Paths + ';' + instlPath + ';' ;
    end;

    { Overwrite (or create if missing) path environment variable }
    if RegWriteStringValue(HKEY_CURRENT_USER, EnvironmentKey, 'Path', Paths)
    then Log(Format('The [%s] added to PATH: [%s]', [instlPath, Paths]))
    else Log(Format('Error while adding the [%s] to PATH: [%s]', [instlPath, Paths]));
end;

And an updated version of EnvRemovePath():

procedure EnvRemovePath(instlPath: string);
var
    Paths: string;
    P, Offset, DelimLen: Integer;
begin
    { Skip if registry entry not exists }
    if not RegQueryStringValue(HKEY_CURRENT_USER, EnvironmentKey, 'Path', Paths) then
        exit;

    { Skip if string not found in path }
    DelimLen := 1;     { Length(';') }
    P := Pos(';' + Uppercase(instlPath) + ';', ';' + Uppercase(Paths) + ';');
    if P = 0 then
    begin
        { perhaps instlPath lives in Paths, but terminated by '\;' }
        DelimLen := 2; { Length('\;') }
        P := Pos(';' + Uppercase(instlPath) + '\;', ';' + Uppercase(Paths) + ';');
        if P = 0 then exit;
    end;

    { Decide where to start string subset in Delete() operation. }
    if P = 1 then
        Offset := 0
    else
        Offset := 1;
    { Update path variable }
    Delete(Paths, P - Offset, Length(instlPath) + DelimLen);

    { Overwrite path environment variable }
    if RegWriteStringValue(HKEY_CURRENT_USER, EnvironmentKey, 'Path', Paths)
    then Log(Format('The [%s] removed from PATH: [%s]', [instlPath, Paths]))
    else Log(Format('Error while removing the [%s] from PATH: [%s]', [instlPath, Paths]));
end;