echo is the basic command for printing in the terminal.

echo puts a newline at the end of every invocation by default:

$ echo "Welcome to Bash"
Welcome to Bash

Simply using double-quoted text with the echo command prints the text in the terminal. Similarly, text without double-quotes also gives the same output:

$ echo Welcome to Bash
Welcome to Bash

Another way to do the same task is by using single quotes:

$ echo 'text in quote'

These methods may look similar, but some of them have got a specific purpose and side effects too. Consider the following command:

$ echo "cannot include exclamation - ! within double quotes"

This will return the following:

bash: !: event not found error

Hence, if you want to print !, do not use within double-quotes or you may escape the ! with a special escape character (\) prefixed with it.

$ echo Hello world !

Or:

$ echo 'Hello world !'

Or:

$ echo "Hello world \!" #Escape character \ prefixed.

When using echo with double-quotes, you should add set +H before issuing echo so that you can use !.

The side effects of each of the methods are as follows:

Another command for printing in the terminal is the printf command. printf uses the same arguments as the printf command in the C programming language. For example:

$ printf "Hello world"

printf takes quoted text or arguments delimited by spaces. We can use formatted strings with printf. We can specify string width, left or right alignment, and so on. By default, printf does not have newline as in the echo command. We have to specify a newline when required, as shown in the following script:

#!/bin/bash 
#Filename: printf.sh

printf  "%-5s %-10s %-4s\n" No Name  Mark 
printf  "%-5s %-10s %-4.2f\n" 1 Sarath 80.3456 
printf  "%-5s %-10s %-4.2f\n" 2 James 90.9989 
printf  "%-5s %-10s %-4.2f\n" 3 Jeff 77.564

We will receive the formatted output:

No    Name       Mark
1     Sarath     80.35
2     James      91.00
3     Jeff       77.56

%s, %c, %d, and %f are format substitution characters for which an argument can be placed after the quoted format string.

%-5s can be described as a string substitution with left alignment (- represents left alignment) with width equal to 5. If - was not specified, the string would have been aligned to the right. The width specifies the number of characters reserved for that variable. For Name, the width reserved is 10. Hence, any name will reside within the 10-character width reserved for it and the rest of the characters will be filled with space up to 10 characters in total.

For floating point numbers, we can pass additional parameters to round off the decimal places.

For marks, we have formatted the string as %-4.2f, where .2 specifies rounding off to two decimal places. Note that for every line of the format string a \n newline is issued.

It should be always noted that flags (such as -e, -n, and so on) for echo and printf should appear before any strings in the command, else Bash will consider the flags as another string.

echo -e "1\t2\t3"
123

echo -e "\e[1;31m This is red text \e[0m"

echo -e "\e[1;42m Green Background \e[0m"