Unix/Linux Shell Programming and Commands

VI (and its improved version Vim) is a text editor for Unix/Linux systems. It's a modal editor with different modes for inserting text and issuing commands. It is not related to telnet, email, or FTP - those are separate network services and clients.

In Unix and Linux command-line environments, the standard command to create a new directory is mkdir followed by the directory name. Other options like newdir or makedir are not standard built-in shell commands.

In Unix and Linux systems, 'cd ..' is the standard command to change the current working directory to the parent directory. 'cd ~' goes to the home directory, and 'cd -' returns to the previous directory.

The pwd command stands for print working directory and is used in Unix-like systems to display the absolute path of the current working directory. The other options are fictional commands.

The kill command sends signals to processes, typically SIGTERM (15) or SIGKILL (9) to stop them. Shutdown is for system-wide power off, stop is not a standard Unix process command, and delete is for removing files not processes.

The whoami command displays the username of the current effective user. pwd shows the present working directory, I and me are not valid Unix commands.

The shell command ':>filename' uses the null command (:) combined with output redirection to truncate an existing file to zero bytes or create a new empty file.

In shell scripting, functions are invoked using the function name followed by parentheses. Without parentheses, the shell would treat it as a command or external program name rather than a function call.

The shell command ':>filename' uses the null command (:) combined with output redirection to truncate an existing file to zero bytes or create a new empty file.

The TZ environment variable sets the timezone for Unix/Linux systems, affecting how time commands display time. It doesn't relate to zombie processes, zip operations, or test conditions.

The parameter expansion ${filename%.} removes the shortest suffix matching ., stripping the extension. So sample.txt becomes sample, not just the extension or with a trailing dot.

Shell functions are called by their name without parentheses, unlike some other languages. Using function1() would try to define it, and there's no 'call' or 'ask' keyword.

Multiple valid methods exist: basename command directly extracts filename, parameter expansion ${Mypath##*/} removes path prefix, or awk splits by '/' to get the last field. The 'file' command shows file type, not filename.

The $? variable holds the exit status of the last executed command, where 0 means success and non-zero means error. $! is PID of last background command, $# is argument count, $@ is all arguments.

In shell scripting, the special variable '$*' holds all command-line arguments passed to the script as a single concatenated string.

The $# variable holds the count of positional parameters passed to a script or function. $* and $@ hold all parameters (as one string or separate arguments), and $? holds the last exit status.

David Korn developed the KornShell (ksh) at Bell Labs as a successor to the Bourne shell, combining features from Bourne shell and C shell.