UNIX for Dummies Questions & Answers

Greetings to everyone,
iam a new unix learner. i just jumped from windows to unix.
in my office iam accessing unix machine thro telnet.
i got this path details after executing the following command echo $PATH
/usr/kerberos/bin:/usr/local/bin:/bin:/usr/bin:/usr/X11R6/bin:/home/mipl/bin.

can anyone explain, why this lengthier path, and what it means and in which location this path is saved.

/usr/kerberos/bin: ?
/usr/local/bin: ?
/bin: ?
/usr/bin:?
/usr/X11R6/bin:?
/home/mipl/bin. ?

please give me full details regarding path. so that i can understand the need of path.

Thanks in advance
Vijay,

/bin is the traditional original location of executables. On modern systems, it is kept fairly small, mostly utilities which are absolutely essential.

/usr/bin is where most day-to-day utilities are installed. Traditionally, /usr was a separate partition, and you could not rely on it being mounted during early start-up.

/usr/local/bin is for locally installed binaries, as opposed to ones installed with the system, or (on modern Unices) via the package management system.

/usr/X11R6/bin is for graphical (X11) programs. I believe it is being phased out in favor of /usr/bin (at least on Debian/Ubuntu).

/home/mipl is probably your home directory, and if you add a bin subdirectory, any utilities you install there will be available to you without an explicit path.

/usr/kerberos is not well standardized, but seems to be a local or platform-specific directory for the Kerberos authentication system (possibly a local directory of binaries recompiled with Kerberos support)?

Basically.....

The path is saved in the environment. Each shell will have some inherited copy of an environment which sets numerous parameters that affect the user. When you execute a command, the path determines where the system looks in order to find the executable. So, in your case, if you execute some command named checkHlrID.pl, the system will look for, in order,
/usr/kerberos/bin/checkHlrID.pl
/usr/local/bin/checkHlrID.pl
/bin/checkHlrID.pl
/usr/bin/checkHlrID.pl
/usr/X11R6/bin/checkHlrID.pl
/home/mipl/bin/checkHlrID.pl
./checkHlrID.pl

In your example that you gave, I believe there should be a : before the last . in the path. The . represents the current directory (where you are at that moment).

It will execute the first instance of the executable that it encounters. So, for instance, if checkHlrID.pl exists in /usr/local/bin and in /usr/X11R6/bin, the system will run the one in /usr/local/bin. If it gets through the entire path without finding a file by the name checkHlrID.pl then it will report that the command was not found. If a file is found by the name checkHlrID.pl but you do not have permission to execute it, then it will report that permission is denied.