JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD MCA 2021 LINUX PROGRAMMING Previous Question Paper (July/August - 2021 - R17)

Shell variables are used to store data in the form of strings, which the shell can access and manipulate. They are categorized into environment variables (inherited by child processes) and local/shell variables (defined within the current shell session). Variables are assigned using the syntax variable_name=value and accessed using the $ prefix.

Example:

Shell meta-characters are special characters that have a specific functional meaning to the shell, rather than being treated as literal text. They are used for pattern matching, redirection, and process control.

Key meta-characters include:

• * (Asterisk): Matches any string of characters, including null. Example: ls *.txt lists all files ending in .txt.
• ? (Question Mark): Matches any single character. Example: ls file?.txt matches file1.txt but not file10.txt.
• [] (Square Brackets): Matches any one of the characters enclosed within the brackets. Example: ls [a-c]* lists files starting with a, b, or c.
• ; (Semicolon): Used to execute multiple commands sequentially on a single line. Example: date; who.
• & (Ampersand): Executes a command in the background. Example: ./script.sh &.
• | (Pipe): Passes the output of one command as input to another. Example: ls | grep 'log'.
• > and >> (Redirection): Used to redirect output to a file, where > overwrites and >> appends. Example: ls > filelist.txt.
• \ (Backslash): Escapes the next character, treating it as a literal rather than a meta-character. Example: echo "Price is \$5" prints the dollar sign literally.