Basic Unix Shell Commands Quiz

Unix Shell Commands Overview

• ls (List Directory Contents): Lists files and directories in the current working directory.

  • ls -l: Long format showing file permissions, link count, owner, group, size, and timestamp.
  • ls -a: Displays all files, including hidden ones (those starting with a dot).
  • ls -h: Formats file sizes to be human-readable (KB, MB).

• mkdir (Make Directory): Creates new directories.

  • Usage: mkdir [directory_name] for a single directory, or mkdir -p [path] for nested directories.

• rmdir (Remove Directory): Deletes empty directories.

  • Usage: rmdir [directory_name] needs the directory to be empty; non-empty directories require rm -r.

• cd (Change Directory): Alters the current working directory.

  • cd [directory_name]: Enter a specified directory.
  • cd ..: Move up one directory level.
  • cd ~: Go to the user's home directory.
  • cd -: Return to the previous directory.

• cat (Concatenate and Display Files): Shows file contents and concatenates multiple files.

  • cat [file_name]: Displays a single file's contents.
  • cat [file1] [file2] > [newfile]: Merges two files into a new file.
  • cat > [newfile]: Creates a new file and enters content (exit with Ctrl+D).

• banner (Create a Large Banner): Produces ASCII-art style text banners.

  • Usage: banner [text] outputs the specified text in a large format.

• touch (Change File Timestamps or Create Empty Files): Updates file timestamps or creates empty files.

  • Usage: touch [file_name] either creates an empty file or modifies the timestamp of an existing file.

• file (Determine File Type): Identifies and displays the type of a given file.

  • Usage: file [file_name] outputs the file type (text, binary, directory, etc.).

• wc (Word, Line, Character, and Byte Count): Counts text elements in files.

  • wc -l: Counts lines.
  • wc -w: Counts words.
  • wc -c: Counts bytes.
  • wc [file_name]: Shows counts for lines, words, and bytes in the specified file.

• sort (Sort Text Files): Arranges lines of text in files.

  • sort [file_name]: Sorts alphabetically by default.
  • sort -r [file_name]: Sorts in reverse order.
  • sort -n [file_name]: Sorts numerically.

• cut (Remove Sections from Each Line of Files): Extracts specific portions from lines of a file.

  • cut -d [delimiter] -f [field_number] [file_name]: Extracts fields using a specified delimiter.
  • cut -c [start]-[end] [file_name]: Extracts characters from defined positions.

• dd (Convert and Copy a File): Performs low-level file copying and conversion.

  • dd if=[source_file] of=[destination_file]: Copies a file from source to destination.
  • dd if=/dev/zero of=[file_name] bs=[block_size] count=[count]: Generates a file filled with zeros.

• dfspace (Show Disk Space Usage): Used to show disk space usage (deprecated).

  • Current command: df -h for human-readable disk space statistics.

• du (Estimate File Space Usage): Displays disk usage of files and directories.

  • du -h: Shows sizes in a human-readable format.
  • du -s [directory_name]: Reports total size of a specified directory.

• ulimit (User Limits): Manages system-wide resource limits for users.

  • ulimit -a: Displays all current resource limits.
  • ulimit -c [size]: Sets limit for core file size.
  • ulimit -n [number]: Sets maximum number of open files.

grep Command

• grep: Stands for "Global Regular Expression Print"; used to search for specific patterns in files.
• Recognized as a powerful command for text searching in Unix.