[SOLVED] Starting programs in shell

[Programmer]

I'm new in Linux and I have a problem with a little thing :

For example when I type this in terminal :

$ cp file.ext /lib/

I pass some arguments to a program called "cp" and it parsing the arguments and in this example it copy a file to a path

I found that some apps that I use in terminal are located in /bin folder and I can access every file that is in /bin folder directly and global

But some apps are not in /bin folder but I can use them in terminal ( for example yum ):confused
In windows there is a variable called PATH that Can be used for make a folder global
has Linux something like this ?

My question is how Linux do it ? I mean how does it recognize the apps that we use in terminal ?

For example I have a file in path :

 /apps/

named exam.py
I want that when I use

$ exam my args

in terminal this file pass to python interpreter and then execute
like :

$ python /apps/exam.py

?

[Misfit138]

You can manipulate a user's path by editing his ~/.bash_profile file. Add directory paths separated by colons and with no intervening space.
For example

export PATH=$PATH:/sbin:/usr/sbin:/usr/bin
export PATH

For root it would be /root/.bash_profile.

Fedora seems to merge /etc/profile on updates, so it seems modifying it is not recommended, though I view it as a more conventional file for global path to be set. You may wish to heed the instruction to create a custom.sh under /etc/profile.d as recommended in that file.

[Programmer]

Can you say how can I do the example that I said ? ---> exam.py

[Misfit138]

Edit your user's /home/user_name/.bash_profile file and add /apps/ after a colon to the PATH= line.
You'll need an editor, of course. gedit, nano, kwrite, kate, vim and joe are examples of editors. Use whichever one you feel comfortable with.

[Gareth Jones]

Originally Posted by Programmer

But some apps are not in /bin folder but I can use them in terminal ( for example yum ):confused
In windows there is a variable called PATH that Can be used for make a folder global
has Linux something like this ?

Others have already answer about PATH, so I'll just add that you can see the current PATH by entering "echo $PATH" into the shell.

The standard directories for software (which should always be in PATH), are /bin (core programs), /usr/bin (the rest of the system), and /usr/local/bin (programs that are not installed by the package manager, e.g. things you've compiled yourself). There are also sbin directories containing administration programs. In F17, /bin and /sbin are going to be replaced with symbolic links to their /usr equivalents.

Occasionally programs are installed in other places, such as /opt/package_name (self-contained packages), ~/bin and ~/.local/bin for personal scripts etc. Also, some commands are shell built-ins, shell aliases or shell functions, and these don't correspond to files.

[SteveGYBE]

There is the utility "which" which prints out where it finds the program on your path

$ which yum
/usr/bin/yum

Yum is a good example, because it's a Python script

$ file /usr/bin/yum
/usr/bin/yum: a /usr/bin/python script, ASCII text executable

Although it's ASCII text - it is marked as executable

$ ls -l /usr/bin/yum
-rwxr-xr-x. 1 root root 801 Mar 16 19:11 /usr/bin/yum

The system knows it should be run using Python by the special entry in the first line of the file (#!' is not a comment, but indicates that the command interpreter to use follows)

$ cat /usr/bin/yum
#!/usr/bin/python
import sys
try:
    import yum
except ImportError:
    print >> sys.stderr, """\
 [ . . . ]

So if you want to run "exam my args":

• Call your file "/apps/exam" (unlike Windows, Linux will not try to guess the file extension of your command, but simply look for what you call it)
• Mark it as executable "chmod a+x /apps/exam"
• Add "/apps" directory to your path "export PATH=$PATH:/apps"
• Add the first line telling it to run the commands using python "#!/usr/bin/python"

[Programmer]

Thanks every one