Unix

Yes, they are the interface to kernel functionality. To quote wikipedia: a system call is how a program requests a service from an operating system's kernel that it does not normally have permission to run

For windows, you might use .cmd, .bat as common file extensions.

Unix doesn't use file extensions as associations, so no file extension needs to be used in the Unix environment. A shell script in Unix is simply a text file with any name that is readable and executable.

However, file extensions are typically used in Unix as a documentation aid that states that the file is a shell script. Common extensions are .sh, .csh, .ksh, .tcsh, .zsh, etc.

Absolute path: Path from root directory (it is the same place, wherever the current path is)

Relative path: Relative to the current path.

Try the following:

ls *[a-z]

The 'pipe' symbol connects the output of one command to the input of another (|)

This command should be used very carefully, and may only be used by the administrative/root account:

vipw

blah blah blah

Lucent

Press the '?' key.

The 'ls' command is an external command (found in /bin)

'smit/smitty' is the administrator tool for configuration in AIX.

STD

Use the builtin 'echo' or 'print' command followed by the shell variable name, which will substitute the value when printed/displayed.

Too difficult to answer here. I would find the source code and use that (if you really had to). Might require a 'port' to another operating system if it wasn't Unix based.

echo $PATH

The principals were Richie and Thompson, along later with Kernighan (for C).

UFS is the main filesystem for FreeBSD, but ZFS is also a popular choice. ext2, msdos, ntfs (read-only), and smb are also supported.

Freely distributable Unix/Linux systems come with the source code, which can be modified.

Proprietary Unix systems are distributed as binary only, with no source code, so you can't modify the system (easily).

Other reasons are legal: the proprietary systems are copyrighted, and the freely distributable versions should not have any copywritten code in them, thus allowing them to be distributed without licensing arrangements.

Systems Administrator :)

You don't mention what you are looking for in terms of a "running configuration file". In Unix/Linux there are many of these. Most of them can be found in the /etc directory or its subdirectories but not all of them are located in /etc.

The filesystem will keep metadata like filename, file permissions, file type (as far as whether it's a regular file, a directory, a named pipe, device file, and so on), file creation and modified date. In addition, if the filesystem being used utilizes inodes, it will also have information on the inode that file is on.

Your question is unclear; Are you talking about reading a filename that happens to contain PDF, or reading a PDF file itself?

The shell script doesn't know or care what kind of files you are using. It all depends on what you intend to do with the file.

There are lots of tasks you can perform with the dd command. The most common would be to create an image file from a disk or partition. Another use would be to create an empty file of an arbitrary size.