JNTU B.Tech III LINUX PROGRAMMING Previous Question Paper (September - 2021 - R15)

Command substitution is a feature in the Linux shell that allows the output of a command to be replaced in the command line. When a command is enclosed in specific tokens, the shell executes the command first, captures its standard output, and replaces the expression with that output before executing the surrounding command.

The tokens used for command substitution are:

1. Backticks (`): The traditional syntax, e.g., `date`.
2. $() syntax: The modern and preferred syntax, e.g., $(date). This method is preferred because it is easier to nest and improves readability.

The cat (concatenate) command is used to display the contents of files, create new files, or append data to existing files. The following shell script demonstrates these functionalities:

#!/bin/bash
# Script to demonstrate cat command

# 1. Display file content
echo "Displaying file content:"
cat file.txt

# 2. Create a new file using cat
echo "Creating newfile.txt..."
cat > newfile.txt <> newfile.txt <