What do I need to read to understand $PATH

I'm new to programming/development and I'm having trouble installing development 开发者_JAVA百科tools.One of my biggest problems when installing something is understanding the shell or terminal (are they the same thing?) and how it relates to installing tools like uncrustify for example. What do I need to read to understand the shell/terminal and $PATH?

Have you tried Googling?

• Environment variable
• PATH (variable)

(I think you're getting good advice so far on PATH)

The most generic description of a shell is that is a program that facilitates interaction w programs. Programs facilitate 'communication' with the OS to perform work by the hardware.

There are two modes that you will normally interact with a shell.

1. a command-line processor, where you type in commands, letter-by-letter, word-by-word until you press the enter key. Then the shell will read what you have typed, validate that it understands the general form of what you have asked for, and then start running the 1 (or more) programs specified in what you have typed.

2. a batch-script processor. In this case you have assembled all of the commands you want executed into a file, and then thru 1 of several mechanisms, you arrange to have the batch-script run so it will in turn run the commands you have specified and the computer does your work for you. Have you done a Windows .Bat file? same idea, but more powerful.

So, a terminal widow is program that is responsible for a. getting input and b., printing output. When you get to the c-programming that underlies the Unix system, you are talking about a feature of the OS design which are called Standard In and Standard Out. Normal unix commands expect to read instructions from StdIn and print output to StdOut.

Of course, all good programs can get their input from files and write there output to files as well, and most programs will take over the StdIn/Out and process files instead of reading input from the keyboard and/or writing to the screen.

To return to the shell, this program that lets you type while the terminal window is open. There are numerous versions of the shell that you may run into AND have varying levels of features that support a. interactive-mode, b. batch-script mode.

To sum it up, here a diagram of what is involved (very basically) for terminal and shell

(run a) terminal-window (program) 
   shell-command-prompt (program) (automatically started as subprogram)
     1. enter commands one at a time, with input from
           a. typed at keyboard (std-in)
           b. infile
        and output to 
           a. screen (std-out)
           b. outFile
    program
       calls OS level functions for 
         a. computation
         b. I/O
 OR 2.
 (run the shell program without a terminal, usually from the cron sub-system)
   shell-batch-processor 
      shell program reads batch-script file, 1 'statement' at a time
      validate statements
      run program, relying on script or cfg to provide inFile data and 
        indicate where to put outfile data.

I hope this helps.