Rosetta Stone
Introduction
Often, people new to a programming language/library have trouble mapping the things they know how to do in other environments to the new environments.
It can be handy to have a sort of "Rosetta stone" that roughly translates tasks from one environment/language into another.
Programming languages
If you have experience in other programming languages (such as C++, Visual Basic), there are some Rosetta stone web pages that might help you. As the Free Pascal/Lazarus syntax and library is fairly consistent with Delphi's, sites that "translate" to Delphi are also a valuable resource.
Some useful pages:
- http://mc-computing.com/Languages/ This page has some explanation of the concepts involved
- http://rosettacode.org/wiki/Category:Pascal A huge number of languages, even esoteric, and tasks, make this site special
- Pascal for C users
- Pascal for CSharp users
- Pascal for Java users
Operating systems
If you know how to do something in an operating system, chances are you can do the same using FPC/Lazarus.
The table below gives a rough mapping of some tasks:
Windows/DOS | Unix/Linux | Description | FreePascal/Lazarus |
assoc | Show/edit file associations | See FileAssociation | |
copy | cp | Copy file | Lazarus fileutil.copyfile; roll your own with filestreams, see e.g. File_Handling_In_Pascal#FileCopy |
date /t | date | Show current date | sysutils.now (date/time); sysutils.date (date); sysutils.time (time) |
del, erase | rm, rm -f | Delete file | sysutils.deletefile, erase |
deltree, rmdir /s | rm -r,rm -rf | Remove directories with subdirectories | Lazarus fileutil.deletedirectory |
dir | ls | Find files in a directory | Lazarus FindAllFiles |
diskpart list volume | mount | Show partitions/volumes/drives on a computer | Windows: see Windows_Programming_Tips#Listing_all_available_drives
Linux: see Linux_Programming_Tips#Get_the_list_of_mounted_partitions Unix: you'll have to parse some files (e.g. /etc/mtab) yourself, depending on Unix flavour; see Forum post |
find | grep | Search for a text/string | Several options, including the pos, ansipos functions. Regular expression support is provided by the RegEx packages. |
ldifde | ldapsearch | Search through Active Directory/LDAP | Use Synapse ldapsend unit to work with LDAP queries; see e.g. example code on Leonardo Ramé's blog |
md5sum | md5sum | Calculate hash of file contents | You can use the MDFile function in the md5 FPC unit. |
mkdir | mkdir | Create directory | mkdir; forcedirectories (creates entire path, if necessary) |
move | mv | Move file to another directory | Within partition/disk: sysutils.renamefile; otherwise copy and delete original |
rename, ren | mv | Rename file | sysutils.renamefile (can also "move" a file between directories, but only on same partition/disk |
sc query <servicename> | service --status-all | Show status for service | See ServiceManager |
? | sed -i 's|Delphi|FreePascal|g' readme.txt | Search and replace text in file. | See example code below. |
shutdown | shutdown | Shut down computer | Windows: see forum post |
tasklist | ps | List or find processes | Windows: Windows_Programming_Tips#Showing.2Ffinding_processes |
? | touch | Create a new empty file | sysutils.filecreate(filename) |
? | touch | Modify file time | See Create a new file date/de |
? | uname | Get kernel/system info | See uname function below. |
wget, curl | wget, curl | Download file from HTTP/FTP | Multiple options, e.g. use synapse httpsend or ftpsend units: Synapse#Downloading_files |
? | which | Search for executable in path | Lazarus fileutil.FindDefaultExecutablePath; see also the example below. |
? | whoami | Find out username | See UserName function below. On Windows: you can check if you're Administrator: winutils.iswindowsadmin(). On *nix: fpgeteuid shows you the effective userid (0 for root). |
Emulating uname
Works on Linux, probably FreeBSD:
program uname;
uses baseunix;
var KernelName: UtsName;
begin
fpuname(KernelName);
writeln(kernelname.sysname);
writeln(kernelname.nodename);
writeln(kernelname.release);
writeln(kernelname.version);
writeln(kernelname.machine);
writeln(kernelname.domain);
end.
Sample output:
Linux mydebianmachine 3.12-1-amd64 #1 SMP Debian 3.12.6-2 (2013-12-29) x86_64 (none)
Emulating which
Although Lazarus has FindDefaultExecutablePath, it has some flaws. Use e.g. this code:
function Which(Executable: string): string;
var
Output: string;
begin
{$IFDEF UNIX}
// Note: we're using external which because
// FindDefaultExecutablePath
// doesn't check if the user has execute permission
// on the found file.
ExecuteCommand('which '+Executable,Output,false);
// Remove trailing LF(s) and other control codes:
while (length(output)>0) and (ord(output[length(output)])<$20) do
delete(output,length(output),1);
{$ELSE}
Output:=FindDefaultExecutablePath(Executable);
{$ENDIF UNIX}
// Extra check:
if (Output<>'') and fileexists(Output) then
begin
result:=Output;
end
else
begin
result:=''; //command failed
end;
end;
Emulating whoami
... or getting the current user's operating system username. Returns a UTF8 string.
uses
{$IFDEF UNIX}
{$IF (DEFINED(LINUX)) OR (DEFINED(FREEBSD))}
,users //not available on OSX
{$ENDIF}
,baseunix //for fpgetuid
.... //other unix stuff
{$ENDIF}
{$IFDEF MSWINDOWS}
,windows
{$ENDIF}
,lazutf8
function UserName: string;
// Get Operating System user name
{$IFDEF WINDOWS}
const
MaxLen = 256;
var
Len: DWORD;
WS: WideString;
Res: windows.BOOL;
{$ENDIF}
begin
Result := '';
{$IFDEF WINDOWS}
Len := MaxLen;
{$IFNDEF WINCE}
// Check for Win98..WinME:
if Win32MajorVersion <= 4 then
begin
SetLength(Result,MaxLen);
Res := Windows.GetUserName(@Result[1], Len);
if Res then
begin
SetLength(Result,Len-1);
Result := SysToUtf8(Result);
end
else
SetLength(Result,0);
end
else
{$ENDIF NOT WINCE}
begin
SetLength(WS, MaxLen-1);
Res := Windows.GetUserNameW(@WS[1], Len);
if Res then
begin
SetLength(WS, Len - 1);
Result := Utf16ToUtf8(WS);
end
else
SetLength(Result,0);
end;
{$ENDIF WINDOWS}
{$IFDEF UNIX}
{$IF (DEFINED(LINUX)) OR (DEFINED(FREEBSD))}
Result := SysToUtf8(GetUserName(fpgetuid));
{$ENDIF}
if Result = '' then
Result := GetEnvironmentVariableUTF8('USER'); //fallback or other unixes which export $USER and don't support GetUserName
{$ENDIF}
end;
Finding all occurrences of some bytes in a file
A sort of grep. From forum post by KpjComp: [1]
The block search class:
unit block_search;
{$mode objfpc}{$H+}
interface
uses
Classes, SysUtils, fgl;
type
{ TBlockSearch }
TBlockSearchResults = specialize TFPGList<int64>;
TBlockSearch = class
private
src:TStream;
fresults:TBlockSearchResults;
block:array of byte;
public
procedure SearchFor(a:array of byte);
constructor Create(_Src:TStream; blocksize:integer = 1024*1024);
destructor Destroy; override;
property Results:TBlockSearchResults read fResults;
end;
implementation
{ TBlockSearch }
procedure TBlockSearch.SearchFor(a: array of byte);
var
readsize:integer;
fPos:Int64;
fifoBuff:array of byte;
fifoSt,fifoEn,searchLen,lpbyte:integer;
//
procedure CheckPos;
var
l,p:integer;
begin
p := fifoST;
for l := 0 to pred(SearchLen) do
begin
if a[l] <> fifoBuff[p] then exit;
//p := (p+1) mod SearchLen, the if seems quicker
inc(p); if p >= SearchLen then p := 0;
end;
fresults.Add(fpos-searchLen);
end;
//
begin
fresults.clear;
src.Position:=0;
readsize := src.Read(block[0],Length(block));
searchLen := length(a);
if searchLen > length(block) then
raise Exception.Create('Search term larger than blocksize');
if readsize < searchLen then exit;
setlength(fifoBuff,searchLen);
move(block[0],fifoBuff[0],searchLen);
fPos:=0;
fifoSt:=0;
fifoEn:=SearchLen-1;
CheckPos;
while readsize > 0 do
begin
for lpByte := 0 to pred(readsize) do
begin
inc(fifoSt); if fifoSt>=SearchLen then fifoST := 0;
inc(fifoEn); if fifoEn>=SearchLen then fifoEn := 0;
fifoBuff[fifoEn] := block[lpByte];
inc(fPos);
CheckPos;
end;
readsize := src.Read(block[0],Length(block));
end;
end;
constructor TBlockSearch.Create(_Src: TStream; blocksize: integer);
begin
inherited Create;
setlength(block,blocksize);
src := _src;
fresults := TBlockSearchResults.Create;
end;
destructor TBlockSearch.Destroy;
begin
freeAndNil(fresults);
inherited Destroy;
end;
end.
Example of usage:
var
bs:TBlockSearch;
..
..
bs := TBlockSearch.Create(SourceFile);
try
bs.SearchFor(WhatIAmSearchingFor);
for i := 0 to bs.results.count-1 do
begin
// Example: we need to do something at an offset after the result
SourceFile.Position := bs.Results.Items[i] + 5;
SourceFile.ReadBuffer(RecordToParse, SizeOf(RecordToParse));
// And now I work on the data in the second packed record of arrays and output to memo or whatever
end;
finally
bs.free;
end;
Search and replace in a file
This will search and replace by loading the entire file into the stringlist in memory and replacing there, then saving the stringlist again. While fine for small files, performance will likely suffer for large files.
procedure FindAndReplace(SearchFor, ReplaceWith, FileName: string);
var
FileContents: TStringList;
begin
FileContents:=TStringList.Create;
try
FileContents.LoadFromFile(FileName);
FileContents.Text:=StringReplace(FileContents.Text, SearchFor, ReplaceWith, [rfReplaceAll,rfIgnoreCase]);
FileContents.SaveToFile(FileName);
finally
FileContents.Free;
end;
end;