Welcome to your first lesson on text processing with Bash! In this lesson, we'll dive deep into the echo command. As you know, the echo command in Bash allows you to print text to the terminal. Though it may seem simple, the echo command is powerful and versatile, and mastering it is essential for formatting messages, debugging scripts, and more. Now, let's dive into the advanced text manipulation with echo.
By default, echo adds a newline character at the end of the output. However, you can suppress this behavior using the -n option.
Bash1#!/bin/bash 2# Default new line 3echo "Greetings" 4echo "Universe" 5 6# Suppress new line 7echo -n "Hello" # Prints "Hello" without newline 8echo "World" # Prints "World" on the same line as "Hello"
Output:
Plain text1Greetings 2Universe 3 4HelloWorld
The first two echo commands by default add a new line at the end of the output. This results in "Greetings" and "Universe" being printed on new lines. By including -n before "Hello", the new line is suppressed resulting in "Hello" and "World" being printed on the same line.
Escape characters are special sequences in a string that denote a particular character that cannot be easily typed or is otherwise reserved. In Bash, escape characters are introduced with a backslash (). They allow you to include characters in your output that have special meanings or are not readily available on the keyboard. To include escape characters in a string, you use the syntax:
Bash1echo -e "..."
When you use the -e option with the echo command, these escape sequences are interpreted and displayed as their corresponding special characters.
Some common escape characters are:
\nfor a new line\tfor a tab\\\for a backslash\"for a quote
Let's look at some examples!
\n is an escape character that represents a newline in a string. When used with the echo -e, it instructs the terminal to move the cursor to the beginning of the next line, effectively splitting the text at that point into multiple lines. Here's an example:
Bash1#!/bin/bash 2echo -e "This is line 1.\nThis is line 2."
Output:
Plain text1This is line 1. 2This is line 2.
Using \n, you can now print multiple lines with a single echo command.
In contrast, omitting -e in the above statement would display:
Plain text1This is line 1.\nThis is line 2.
\t is an escape character that represents a horizontal tab in a string. When used with echo -e, it inserts a tab space at the specified position in the text, creating a gap between text segments. In Bash, \t is typically 4 to 8 spaces but it is configurable. Here's an example:
Bash1#!/bin/bash 2echo -e "Column1 \tColumn2 \tColumn3"
The output is:
Plain text1Column1 Column2 Column3
The \t special character is great for formatting output into columns or aligning text.
Double quotes are used to define string literals. When you open a string with a double quote ("), Bash expects the string to be closed by the next double quote. For example, "Name: "Cosmo" " results in an error because Bash interprets the quote before C as the closing quote of the string. To include double quotes in a string, you add a \ beforehand. Let's look at an example:
Bash1#!/bin/bash 2echo -e "Welcome to this lesson titled \"Text Formatting with Echo\""
The output is:
Plain text1Welcome to this lesson titled "Text Formatting with Echo"
Including quotes in your strings is essential for properly formatting quoted phrases or titles.
Windows-style file paths use backslashes (\) as separators between directory levels, which is different from Unix-like systems that use forward slashes (/). You might be wondering how to include a \ in such a string. Bash expects the text after \ to be an escape character that has special meaning like n or t. Let's take a look at an example.
Bash1echo -e "C:\temp"
The output is:
Plain text1C: emp
Bash interprets the t in temp as the tab character. Just like n and t, \ is also an escape character. To include a \ in a string, you just use \\\. For example:
Bash1#!/bin/bash 2echo -e "C:\\\Users\\\Cosmo\\\report.txt"
The output is:
Plain text1C:\Users\Cosmo\report.txt
Using \\\ is essential for correctly displaying file paths or other text containing backslashes in your output.
The echo command can also be used to display colored text using ANSI escape codes. The syntax to change the color of text is:
Bash1echo -e "\e[<ANSI_code>m<Your text>\e[0m"
\e: This initiates the ANSI escape sequence.[<ANSI_code>m: This is the ANSI escape code for setting text formatting attributes, such as color. The<ANSI_code>is a specific number that represents a particular color.-
<Your text>is the actual text you want to print in the specified color.
\e[0m: This sequence resets the text attributes (including color) back to their default settings. This ensures that any text printed after this sequence appears in the default color and formatting.
Let's take a look at an example:
Bash1#!/bin/bash 2echo -e "\e[31mThis text is red.\e[0m" # Prints red text 3echo -e "\e[32mThis text is green.\e[0m" # Prints green text
\e[31mstarts red-colored text.\e[32mstarts green-colored text.\e[0mresets the color back to the default.
The output is:
Here is a list of some common color codes:
30: Black31: Red32: Green33: Yellow34: Blue35: Magenta36: Cyan37: White
Fantastic work! In this lesson, you learned how to:
- Use
-nto suppress new lines - Use
-eto enable backslash escapes - Use
\nto create new lines - Use
\tto insert tab spaces - Print special characters like backslashes (
\\\) and quotes (\"). - Display colored text using ANSI escape codes.
As you continue with this course, you'll integrate these techniques with more advanced text-processing tools like grep, sed, and awk. Now, jump into the practice section to reinforce what you've learned and get hands-on experience with echo. Happy scripting!