The calc command is a Unix command that allows you to perform simple calculations from the command line. It can be used to calculate basic arithmetic operations, such as addition, subtraction, multiplication and division, as well as to compare numbers and evaluate mathematical functions. For example, calc 2 + 2 will return the result 4. For more information about calc, refer to the man page.

A shell script is a computer program designed to be run by the Unix/Linux shell, which is a command-line interpreter. It typically automates a sequence of commands or actions that would otherwise be performed one-by-one by a human operator. Shell scripts are written in a scripting language that is interpreted by the shell, such as Bash, and can be used for a variety of purposes such as system administration, file manipulation, and automation tasks. Here is an example of a simple Bash shell script:

bash
 
 
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#!/bin/bash
# This is a comment

echo "Hello, world!"

This script uses the echo command to output the string "Hello, world!" to the terminal. The first line (#!/bin/bash) tells the shell which interpreter to use (in this case, Bash) to run the script.