Echo command instance

Echo command instance

The echo command is a built-in shell command used to display the value of a variable or print a line of text.

The echo command plays an important role in building shell scripts.

Syntax:

1. # Echo [Options] [String]

The items in square brackets are optional. A string can be defined as a finite sequence of characters (such as letters, numbers, symbols, and punctuation marks ).

When the echo command is used without any options or strings, it returns a blank line on the display screen, followed by another line to keep up with the command prompt. This is because pressing the Enter key means sending a signal to the system to start a new line, and echo repeats the signal.

Option:

• -N: Do not output new lines.
• -E enable backslash escape Interpretation
• -E disable backslash escape interpretation (default)

If you use the-e option, you can use the following escape sequence:

• \ Backslash
• \ A warning (BEL)
• \ B backslash
• \ C does not generate further output
• \ E escape
• \ F form feed
• \ N New Line
• \ R newline character
• \ T horizontal tabulation
• \ V vertical tabulation
• Byte NNN (1 to 3 digits) represented by \ 0NNN octal values)
• \ XHH hexadecimal value indicates the byte NNN (1 to 2 digits)

10 Linux Interview Questions and Answers in different application scenarios

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Example: 1. display the value of the system-defined variable

Using the set command, we can list system-Defined variables. To print the values of these variables, we can use the echo command:

1. Jack @ localhost :~ $ Echo $ USER
2. Jack
3. Jack @ localhost :~ $ Echo $ HOME
4. /Home/jack

Example: 2. display the value of a user-defined variable

1. Jack @ nextstep4it :~ $ Var1 = 'date'
2. Jack @ nextstep4it :~ $ Echo "Today's date time is: $ var1"
3. Today's date time is: Mon Jul 28 13:11:37 IST 2014

Example: 3. display a text string

1. Jack @ nextstep4it :~ $ Echo "Hi this echo command testing"
2. Hithis echo command testing

Example: 4 Use the backslash in the echo command

1. Jack @ nextstep4it :~ $ Echo-e "Ubuntu \ bis \ bthe \ bbest \ bDesktop \ bOS"

The above command will print:

Ubuntuisthebest1_topos

Example: 5 use a tab space in the echo command

1. Nextstep4it @ nextstep4it :~ $ Echo-e "Ubuntu \ tis \ tthe \ tbest \ tDesktop \ tOS"

The above command will display the following output:

Ubuntu is the best Desktop OS

Example: 6 Use vertical tabs in the echo command

1. Jack @ nextstep4it :~ $ Echo-e "Ubuntu \ vis \ vthe \ vbest \ vDesktop \ vOS"
2. Ubuntu
3. Is
4. The
5. Best
6. Desktop
7. OS

Example: 7. Set the color output of the echo command

The echo command can modify the font type, background color, and font color. The escape sequence \ 033 can be used to change the font attributes. To make the escape sequence take effect, you must use the-e option. Some escape codes are listed below:

• [0 m: normal
• [1 m: bold
• [4 m: The font is underlined
• [7 m: reverse foreground and background color
• [8 m: invisible characters
• [9 m: cross-line font
• [30 m: Gray
• [31 m: red
• [32 m: green font
• [33 m: Brown
• [34 m: Blue font
• [35 m: Purple font
• [36 m: light blue font
• [37 m: light gray font
• [38 m: Black font
• [40 m: black background
• [41 m: red background
• [42 m: green background
• [43 m: brown background
• [44 m: blue background
• [45 m: purple background
• [46 m: light blue background
• [47 m: light gray background

The following command prints the output in red.

1. Jack @ nextstep4it :~ $ Echo-e "\ 033 [31 mMagic of Linux \ 033 [0 m"
2. Magic of Linux

The following command prints "Magic of Linux" in bold and red ".

1. Nextstep4it @ nextstep4it :~ $ Echo-e "\ 033 [1 m \ 033 [41 mMagic of Linux \ 033 [0 m"
2. Magic of Linux

Via: http://www.nextstep4it.com/categories/unix-command/echo-command/

Translator: GOLinux Proofreader: wxy

This article was originally translated by LCTT and launched with the Linux honor in China

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