Linux Command Line Fundamentals

The 'shutdown' command is used to power off or reboot a Linux system. The '-h' flag stands for halt (power off).

The 'find' command is used to search for files. The '-mtime -1' flag filters for files modified within the last 24 hours (1 day).

The 'basename' command extracts the filename, and 'xargs' is used to execute the copy command for each file found, appending '_bk' to the new filename.

The 'df' command (disk free) reports file system disk space usage. The '-h' flag makes the output human-readable (e.g., GB, MB).

The 'du' command (disk usage) estimates file space usage. The '-s' flag provides a summary, and '-h' makes it human-readable.

The 'fg' command brings a background job to the foreground. 'bg' sends a process to the background, and 'kill' terminates it.

The 'jobs' command lists active jobs running in the current shell session's background.

CTRL+Z sends the SIGTSTP signal to the current process, which suspends it and allows the user to move it to the background.

The 'ps' command (process status) displays information about active processes. The 'aux' options are commonly used to show all processes for all users.

The kill command is the standard utility for terminating processes in Unix-like systems. Providing a process ID (PID) allows the user to target a specific process for termination.

CTRL + C sends the SIGINT signal to the foreground process, which typically causes it to terminate immediately. Other options like CTRL + Z suspend a process, and CTRL + D signals end-of-file.

The pipe operator (|) connects the standard output of the command on its left to the standard input of the command on its right. This is a fundamental feature of Unix shell pipelines.

The less-than symbol (<) is used for input redirection, which takes the contents of a file and feeds them into a program as standard input.

In shell redirection, 2 represents the file descriptor for standard error (STDERR). Using 2> redirects this specific stream to a file.

The double greater-than operator (>>) appends the output to a file rather than overwriting it, which is the behavior of the single > operator.

The greater-than symbol (>) is the standard operator for redirecting standard output to a file, overwriting the file if it already exists.

grep stands for Global Regular Expression Print; it is the standard command-line tool for searching text within files or streams for a specific pattern.

wc (word count) displays newline count, word count, and byte count. This answers 'how many' questions about file content. The question wording is awkward but the answer is correct.

The sort command is used to arrange lines of text files or input streams in a specific order, such as alphabetical or numerical.

The tail command displays the end portion of a file or stream, which is useful for monitoring logs or checking the end of a document.

The head command displays the beginning portion of a file or stream, by default showing the first 10 lines.

chmod (change mode) is the command used to modify the access permissions of file system objects.

The ls command lists directory contents. The -l flag enables the long listing format, which displays permissions, owner, size, and modification time.

In the standard Unix permission triplet (rwx), the 'x' character stands for execute permission.

In the standard Unix permission triplet (rwx), the 'w' character stands for write permission.

In the standard Unix permission triplet (rwx), the 'r' character stands for read permission.

Square brackets [ ] are used in globbing to specify a range or set of characters to match, such as [a-z] or [0-9].

The question mark (?) is a wildcard that matches exactly one single character in a filename.

The asterisk (*) is a wildcard that matches zero or more characters in a filename.

The rm command (remove) is used to delete files or directories in Unix-like systems.

The mv command (move) is used to move files or directories from one location to another, and it is also used for renaming.

The cp command (copy) is used to duplicate a file or directory from a source to a destination.

The touch command is primarily used to update the timestamps of a file, but it also creates an empty file if the specified file does not already exist.

The rmdir command (remove directory) is specifically designed to delete empty directories.

The mkdir command stands for make directory. It is the standard utility for creating new directories in a Unix-like filesystem.

The man command with the -k flag performs a keyword search through the manual page descriptions. This is equivalent to using the apropos command.

To view the manual page for a specific command, you simply type man followed by the command name. This opens the documentation for that tool.

The file command examines a file to determine its type, such as whether it is a text file, an executable, or a directory. It looks at file headers rather than just the extension.

In most Linux shells, pressing the TAB key triggers command or path completion. This is a standard feature for efficiency and accuracy.

In filesystem paths, two dots (..) represent the parent directory of the current location. This is used to navigate up the directory tree.

A single dot (.) is a special reference to the current directory. It is often used in paths to explicitly indicate the current location.

The tilde (~) is a shorthand character in Linux shells that expands to the path of the current user's home directory.

A relative path describes the location of a file or directory starting from the current working directory. It does not begin with a forward slash.

An absolute path provides the full path to a file or directory starting from the root directory (/). It always begins with a forward slash.

A path is the unique location of a file or directory in the filesystem hierarchy. It acts as an address for the system to find the resource.

The cd command stands for change directory. It is used to navigate between directories in the filesystem.

The ls command lists the contents of a directory. It is the standard tool for viewing files and subdirectories within a given path.

The pwd command stands for print working directory. It outputs the full path of the directory you are currently in.