How does the path environment variable work? - variables

I know how to add values to the path variable, so my question is not how to use it.
Rather, I want to know how it works under the hood. When you type in the name of a program to execute, how does the system make use of PATH to find the matching program? How does it know when it finds a match?

for example...
when you set c:\python27\ into your environment path...
and you goto cmd, you are at c:\ and you type python
cmd knows to check the environment path which it will find c:\python27\ among others. then it looks for the command in each path listed in your environment paths
then executes the command if it finds it
simply the env path tells where to look for the command if it is not in the current directory

Related

How to use alias for opening file from its absolute path in csh

I want to create an alias, which will take file name, get its path and open it by gvim.
Something like this:
alias gg "gvim `which \`"
usage:
> gg some_file_in_remote_path
But I cannot make it work in csh.
Can someone help please
The command "which" gets a full path of of shell commands.
It does not find the full path of of every file you have in your system.
The command you are looking for is "find", although searching the entire file system could be time consuming. Perhaps install "locate" and use that instead of find. Even then you would have to decide in your script what to do when multiple files have the same name.

Check if Windows batch variable starts with a specific string

How can I find out (with Windows a batch command), if, for example, a variable starts with ABC?
I know that I can search for variables if I know the whole content (if "%variable%"=="abc"), but I want that it only looks after the beginning.
I also need it to find out where the batch file is located, so if there is a other command that reveals the file's location, please let me know.
Use the variable substring syntax:
IF "%variable:~0,3%"=="ABC" [...]
If you need the path to the batch file without the batch file name, you can use the variable:
%~dp0
Syntax for this is explained in the help for the for command, although this variable syntax extends beyond just the for command syntax.
to find batch file location use %0 (gives full patch to current batch file) or %CD% variable which gives local directory

TCL: how to execute program using enviorment PATH variable

I've got following line in my script
exec $::env(PATH)/program.exe
In my env PATH variable I've got a directory where I've got this executable file. For example:
PATH env variable got among other this - D:\my_program\bin
I've got error:
Error:
couldn't execute C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;D:\my_program\bin;\program": no such file or directory
Any suggest how to execute .exe file using system variable like PATH in tcl?
Thanks
PS
OK, when I've create a new env variable (PATH1 - without any other paths, just one) and set .exe file path to it, it seems to work. Any solution to do with PATH (with multiple paths) excluding set D:\my_program\bin in first place?
You should simply use the Tcl library function made for this auto_execok.
Try this:
exec {*}[auto_execok program.exe]
It automatically searches the PATH and constructs the right path for using with exec.
For example, to start notepad.exe:
% auto_execok notepad.exe
C:/windows/system32/notepad.exe
% exec {*}[auto_execok notepad.exe]
To see why the {*} is needed, have a look at http://wiki.tcl.tk/765. Basically auto_execok is pretty smart and can return a list, if needed, e.g. for running start on windows, which needs the expansion to work properly with exec.

batch scripting: how to get parent dir name without full path?

I'm working on a script that processes a folder and there is always one file in it I need to rename. The new name should be the parent directory name. How do I get this in a batch file? The full path to the dir is known.
It is not very clear how the script is supposed to become acquainted with the path in question, but the following example should at least give you an idea of how to proceed:
FOR %%D IN ("%CD%") DO SET "DirName=%%~nxD"
ECHO %DirName%
This script gets the path from the CD variable and extracts the name only from it to DirName.
You can use basename command:
FULLPATH=/the/full/path/is/known
JUSTTHENAME=$(basename "$FULLPATH")
You can use built-in bash tricks:
FULLPATH=/the/full/path/is/known
JUSTTHENAME=${FULLPATH##*/}
Explanations:
first # means 'remove the pattern from the begining'
second # means 'remove the longer possible pattern'
*/ is the pattern
Using built-in bash avoid to call an external command (i.e. basename) therefore this optimises you script. However the script is less portable.

Windows 7 environment variable not working in path

I am trying to set up some path using environment variable.
I added an environment variable "MAVEN_HOME" with the value "C:\maven".
Then in the path I added "%MAVEN_HOME%\bin;...rest".
When I type "echo $MAVEN_HOME%" I get the correct "C:\maven" printed on the screen.
But when I type "mvn" which is a batch file in the "bin" directory, it can't find it.
So, I manually added the entire path in PATH.
"C:\maven\bin;...rest"
and it was able to find "mvn" and execute it.
Could someone help me what I did wrong?
Check if there is a space character between the previous path and the next:
Incorrect:
c:\path1; c:\Maven\bin\; c:\path2\
Correct:
c:\path1;c:\Maven\bin\;c:\path2\
I had exactly the same problem, to solve it, you can do one of two things:
Put all variables in System Variables instead of User and add the ones you want to PATH
Or
Put all variables in User Variables, and create or edit the PATH variables in User Variable, not In System. The Path variables in System don't expand the User Variables.
If the above are all correct, but the problem is still present, you need to check the system Registry, in HKEY_CURRENT_USER\Environment, to make sure the "PATH" key type is REG_EXPAND_SZ (not REG_SZ).
My issue turned out to be embarrassingly simple:
Restart command prompt and the new variables should update
Things like having %PATH% or spaces between items in your path will break it. Be warned.
Yes, windows paths that include spaces will cause errors. For example an application added this to the front of the system %PATH% variable definition:
C:\Program Files (x86)\WebEx\Productivity Tools;C:\Sybase\IQ-16_0\Bin64;
which caused all of the paths in %PATH% to not be set in the cmd window.
My solution is to demarcate the extended path variable in double quotes where needed:
"C:\Program Files (x86)\WebEx\Productivity Tools";C:\Sybase\IQ-16_0\Bin64;
The spaces are therefore ignored and the full path variable is parsed properly.
%M2% and %JAVA_HOME% need to be added to a PATH variable in the USER variables, not the SYSTEM variables.
If there is any error at all in the PATH windows will silently disregard it. Things like having %PATH% or spaces between items in your path will break it. Be warned
Also worth making sure you're using the command prompt as an administrator - the system lock on my work machine meant that the standard cmd just reported mvn could not be found when typing
mvn --version
To use click 'start > all programs > accessories', right-click on 'command prompt' and select 'run as administrator'.
To address this problem, I have used setx command which try to set user level variables.
I used below...
setx JAVA_HOME "C:\Program Files\Java\jdk1.8.0_92"
setx PATH %JAVA_HOME%\bin
NOTE: Windows try to append provided variable value to existing variable value. So no need to give extra %PATH%... something like %JAVA_HOME%\bin;%PATH%
If the PATH value would be too long after your user's PATH variable has been concatenated onto the environment PATH variable, Windows will silently fail to concatenate the user PATH variable.
This can easily happen after new software is installed and adds something to PATH, thereby breaking existing installed software. Windows fail!
The best fix is to edit one of the PATH variables in the Control Panel and remove entries you don't need. Then open a new CMD window and see if all entries are shown in "echo %PATH%".
I had this problem in Windows 10 and it seemed to be solved after I closed "explorer.exe" in the Task Manager.
In my Windows 7.
// not working for me
D:\php\php-7.2.6-nts\php.exe
// works fine
D:\php\php-7.2.6-nts
I had the same problem, I fixed it by removing PATHEXT from user variable. It must only exist in System variable with .COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC
Also remove the variable from user to system and only include that path on user variable
Copy the value of path to notepad and check if this corresponds with the echo %path% in terminal window and make changes if needed. Then delete the old path value and paste the notepad value back in.
I assume some invisible character entered there by some installation corrupted the path value.
Make sure both your System and User paths are set correctly.