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Significance of a PATH explained

This is probably a rudimentary question but I am still kinda new to programming and I've wondered for awhile. I've done multiple projects in Python, C#, and Java, and when I try to use new libraries (especially for Python) people always say to make sure its in the right PATH and such. I just followed an online tutorial on how to install Java on a new computer and it rekindled my question of what a path really is. Is the Path just were the programming language looks for a library in the file system? I get kinda confused on what it's significance is. Again, I'm sorry for the wide question, its just something that I've never quite gotten on my own programming.
EDIT: I just wanted to thank everyone so much for answering my question. I know it was a pretty dumb one now that I've finally figured out what it is, but it really helped me. I'm slowly working through as many C#, Java and Python tutorials as I can find online, and it's nice to know I have somewhere to ask questions :)

The PATH is an environment variable which the shell (or other command interpreter) uses to search for commands. Usually (always?) commands are found with a greedy algorithm, so entries that come first in the PATH are returned first. For example, a command in /usr/local/bin will override a command in /usr/bin given a PATH such as
$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
while the purpose is consistent, the syntax is slightly different on WINDOWS - you would use
C:\> ECHO %PATH%
to "echo" your PATH.
First my shell is going to search /usr/local/sbin then /usr/local/bin then /usr/sbin and then /usr/bin before searching /sbin and /bin if the command isn't found then it will report that it couldn't find such a command...
# Like so
$ thisprogramdoesntexist
thisprogramdoesntexist: command not found
Now, on Linux at least, there's also a LD_LIBRARY_PATH which the system will use to search for dynamic libraries (greedily), on Windows I think it just uses the PATH. Finally, Java uses a CLASSPATH which is similar (but used to search for classes and JARs).
On Linux one might add an entry to the PATH like so,
$ export PATH="$PATH:/addNewFolder"
While on Windows you might use
set PATH=%PATH%;c:\addNewFolder
Sometimes, you might manipulate your PATH(s) to enable specific functionality, see update-java-alternatives on Ubuntu for an example.

A PATH is a file directory on your computer. If you need to install a programming language, you might need to put it in your system PATH variable. This means that the system looks to these files for different information, IE where the libraries for the code you are using are.
Hope that helped!

Exactly as other said, PATH is a list of folders that is included in the search -other than the current folder- and you can always access straight away. It's one of the Environment Variables.
For example, we have the python folder in C:\Python27. I'm sure you know that to run a python file, we commonly use python script.py.
What happens is that the command line searches for python.exe in your current folder, and if not found, search it in the folders in the path variable.
To read the path, you can, straightforwardly use:
$ PATH
If you're on windows, like i am, an easy way to deal with this is to just use System Properties. Just type it in the start menu, open it, and go to the 'advanced' tab. Click on the Environment Variables, there! You'll see a PATH variable, and you can modify it as you want.
I myself use more than one version of Python, and to deal with this, i appended all the folders to PATH, and changed my python.exe to pythonversion_number.exe. Problem solved! Now, i can run this in the command line:
$ python26 script.py
$ python33 script2.py
Some further reading on this, if you're interested, here's a good question asked
Hope this helps!

The best resource (so far) about PATH information, you can see in this question:
https://superuser.com/questions/284342/what-are-path-and-other-environment-variables-and-how-can-i-set-or-use-them
Stack Overflow is not the best place to search about this, always check the amazing
https://superuser.com/ for this kind of question.

PATH is a symbolic name usually associated to string values separated by a semicolons (where each string part is a directory name). This symbolic name (and its values) is handled by the operating system and could be modified by the end user through the some command line instruction like SET PATH=........ or through some kind of user interface configuration tool.
It is common practice for tools like compilers or other programming tools to look at this symbolic name and use the list of string values for searching files that are not directly available in the current folder used by the tools.
So, if an installation procedure set the PATH symbol in this way
SET PATH=%path%;C:\PROGRAM FILES\MYTOOLFOLDER;
it means, set the PATH symbol to the previous value (%PATH%) and add another string value to it (C:\PROGRAM FILES\MYTOOLFOLDER).
Then the tool, when it needs to search for a particular file or library, could read the PATH symbol values, split them at the semicolons and iteratively look at the directories listed one by one looking for the file required.
In C# programming, for example, the tool code could contain something like this
string pathSymbol = Environment.GetEnvironmentVariable("PATH");
string[] pathFolders = pathSymbol.Split(';');
foreach(string folder in pathFolders)
{
if(File.Exists(Path.Combine(folder, "mylibrary.dll"))
{
..... do whatever you need to do with the file
}
}
This example assumes a Windows environment.

How to get full path to file that "knows" when working in debugger

I have an XML file I'm streaming as an XDocument. I need to be able to get the full path of the file (NOT the bin/Debug path) using reflection or the like (so this will be the path from the User's machine it lives on).
I have tried about a zillion different ways, including:
System.Reflection.Assembly.GetCallingAssembly().Location
System.Reflectin.Assembly.GetEntryAssembly().Location
System.Reflection.GetExecutingAssembly().Location
AppDomain.CurrentDomain.BaseDirectory.
How do I look use System.IO to find the path on the User's machine to my file?? Quite suprised I haven't found the simple answer after googling all day.
::EDIT:: I've now found out that there is no way to "reflectively" locate a path dynamically based on whether the application is running in the debugger or not. My only option is to do some detection.
Thanks in advance!!

I'm assuming that the file is in a child directory of the executable?
You can get the full path of the current working directory (ie where your .exe was run from) by using the Environment class. You can then concatanate this with the child directory
Environment.CurrentDirectory + #"\folder\file.xml"
http://msdn.microsoft.com/en-us/library/system.environment.aspx
Hope this helps!
EDIT: After reading up a little it turns out that CurrentDirectory can be changed rather easily. The accepted answer here Environment.CurrentDirectory is yielding unexpected results when running installed app offers a more reliable method.

Found my answer here (using path stripping and GetFullPath() ). It's a real bummer there's no way around just stripping the bin/debug part of the path. I used the third part of the question linked above.

Read SQL query file from project directory

I've put 3 especially large SQL queries within my Visual Studio project, under a folder "Queries" that is in the project directory (not the solution). Is there an eloquent way to access these files? I was hoping that something like #"Queries/firstSqlQuery.sql would work.
Specifying the full path, like with #"C:\\Users\John\Documents\VisualStudio2010\Projects\MySolution\MyProject\Queries\firstSqlQuery.sql
is something I'd really rather not do, since it requires me to go back into code and fix the path, should the application move.
EDIT: For some reason, the page is looking for the files in C:\\Program Files(x86)\Common Files\Microsoft Shared\DevServer\Queries\firstSqlQuery.sql. Why is it looking in this location, when the executable directory is different?

You can do something like this... if it's outside of project. (When I intitially read this-- I misread and thought it was in the solution directory which I was assuming contained the project)--
var pathToBin = Assembly.GetExecutingAssembly().Location;
var directoryInfoOfBin = new DirectoryInfo(pathToBin);
var solutionDirectory = directory.Parent().Parent();
var pathToSolution = solutionDirectory.FullName;
but this is much simpler if it's in the project
System.Web.HttpContext.Current.Server.MapPath("~/Queries/firstSqlQuery");

There are a number of ways to handle this, but there is a fundamental understanding you must gather first. Issuing something like #"Queries/..." isn't, by itself, isn't going to do anything. You need to leverage the System.IO namespace to perform IO operations.
With that part of the foundation, let's lay some more, when you issue a command like this:
File.ReadAllText("firstSqlQuery.sql");
the path that is implied is the Working Directory of the assembly that's executing the code. When debugging an application in Visual Studio, especially and ASP.NET Application, that's the bin directory that resides under the project directory, by default. So, if you did want to access the Queries folder, you would have to do something like this:
File.ReadAllText(#"..\Queries\firstSqlQuery.sql");
so, that's one way of handling it.
Another way of handling it would be to copy the file over into the bin folder every time the project is built by looking at the file properties (e.g. create a Post Build Event), but that's more work than I think you're looking for.
Again, the key here is to understand what directory you're starting in.
Finally, one thing worth noting, if you leverage the directory structure you'll need to ensure that the Queries folder gets deployed to the live site. That probably goes without saying, but I've seen people run into that exact problem before.

You could make sure your query files are copy to the output directory when you do a build and read the files from there without having to set a path.

Finding Install path of a program

I am new to C# and I have made a simple Windows Forms Application that basically updates the persons files for a game.
They have to manually move and delete certain folders just to change version every time. I have successfully accomplished this.
However before I start giving it out I really should improve it. I know I need to change the name of the processes and remove my descriptions ETC.
I have stumbled onto an error and instead of me taking a guess I think it is best to get an opinion from a more experienced person about how to do this.
I am going to use Inno Setup to make the installer for my application, this way I can be sure it will go into their program files 32 and 64 bit. So I know this will be in program files.
So now I am wondering if I have done this the correct way or not? I was using this format to find their program files:
string programFilesFolder = Environment.GetEnvironmentVariable("PROGRAMFILES(X86)") ?? Environment.GetFolderPath(Environment.SpecialFolder.ProgramFiles);
However, would this work on all windows systems(XP, Vista, Win7, Win8) and is it completely accurate? I was going to use the above, and then use this:
string PATCHSELECTOR = Path.Combine(programFiles, #"PATCH SELECTOR");
if (Directory.Exists(PATCHSELECTOR))
{
string GamereliteFolder = Path.Combine(programFiles, #"GAMERELITE~1");
if (Directory.Exists(GamereliteFolder))
And then I move the files using the string method. If the file exists it is deleted before I copy the file over from PATCH SELECTOR to GAMERELITE.
Also will windows XP support using the .exe with an assembly resource embedded which is making the program need to be ran as administrator? I previously was making the assembly work through UAC however that wouldnt always work if they have UAC off or if it is XP so I thought I would try the admin assembly instead.
Can anyone possibly give me some insight, ideas or links?

For executables (not sure for websites & web application) this returns the directory where the executable lives (it's actually the base path where the framework will probe for Assemblies to load, 99% of the the that's the same thing).
System.AppDomain.CurrentDomain.BaseDirectory

This method works for any executable located in a folder which is defined in the windows PATH variable:
private string LocateEXE(String fileName)
{
string path = Environment.GetEnvironmentVariable("path");
string[] folders = path.Split(';');
foreach (var folder in folders)
{
if (File.Exists(Path.Combine(folder, fileName)))
{
return Path.Combine(folder, fileName);
}
}
return String.Empty;
}
Usage:
string pathToEXE = LocateEXE("Example.exe");
Reference:
how to find the execution path of a installed software
How can I get another application's installation path programmatically?

Couple things:
Among the already stated answers, Assembly.GetExecutingAssembly().Location will also give you the full file path of the currently "executing" Assembly. (Alternatively, GetCurrentAssembly)
If I'm reading your question correctly, you're trying to find both your own location as well as another application's. I would highly recommend seeing if the other application has a registry key that specifies the exact location - it'll make your copy step WAY more stable.

Get Correct folder using c#

so, i am building a new WinForms with update my program.
the thing is, i am not installing any-thing. so,when i give my freinds my program, that can put it where ever they want. how can i know where did they put it?
like, lets say my program called "MyProg".
so lets say my freind puted "MyProg" in C:\programs\install\SayHello.
and i want my program to know where she is and save it to xml(everytimes she loads).
so, i know how to use everything here, i just need to know how can i get the folder path i am in now. (for my explined the foldepath = "C:\programs\install\SayHello.")
Anyone?
Thanks again,
Alon. :)

From How do I get the name of the current executable in C#?, to find the name of the currently running assembly:
string file = object_of_type_in_application_assembly.GetType().Assembly.Location;
string app = System.IO.Path.GetFileNameWithoutExtension(file);
so to find the path of the currently running assembly
string file = object_of_type_in_application_assembly.GetType().Assembly.Location;
string path = System.IO.Path.GetDirectoryName(file);
should do the job.
Environment.CurrentDirectory won't necessarily return what you want, as it's possible to run the program from a different folder at the console.

There are a few options, including:
Application.ExecutablePath
Search for "get exe location c#" for more variations on this.

Environment.CurrentDirectory contains the current directory.

Application.StartupPath
should do the same in your case.