echo command is built in shell command , which used to display the value of a variable or print a line of text. Echo command plays a important role in building a shell script.
Synatx :
# echo [Options] [String]
The items in square brackets are optional. A string can be defined as finite sequence of characters (like letters, numerals, symbols punctuation marks).
When echo command is used without any options or strings, echo returns a blank line on the display screen followed by the command prompt on the subsequent line. This is because pressing the ENTER key is a signal to the system to start a new line, and thus echo repeats this signal.
Options :
- -n do not output the trailing newline
- -e enable interpretation of backslash escapes
- -E disable interpretation of backslash escapes (default)
If -e is in effect, the following sequences are recognized:
- \\ backslash
- \a alert (BEL)
- \b backspace
- \c produce no further output
- \e escape
- \f form feed
- \n new line
- \r carriage return
- \t horizontal tab
- \v vertical tab
- \0NNN byte with octal value NNN (1 to 3 digits)
- \xHH byte with hexadecimal value HH (1 to 2 digits)
Example :1 Display the value of System Defined Variables
Using the set command , we can list the system define variables and to print the vaule of these variables we can use echo command :
jack@localhost:~$ echo $USER jack jack@localhost:~$ echo $HOME /home/jack
Example:2 Display the value of User defined Variables :
jack@nextstep4it:~$ var1=`date` jack@nextstep4it:~$ echo "Today's date time is : $var1" Today's date time is : Mon Jul 28 13:11:37 IST 2014
Example:3 Display the text String
jack@nextstep4it:~$ echo " Hi this echo command testing" Hi this echo command testing
Example:4 Use of backspace in echo command
jack@nextstep4it:~$ echo -e "Ubuntu \bis \bthe \bbest \bDesktop \bOS"
Above Command will Print :
UbuntuisthebestDesktopOS
Example:5 Use of tab space in echo command
nextstep4it@nextstep4it:~$ echo -e "Ubuntu \tis \tthe \tbest \tDesktop \tOS"
Above command will show below output :
Ubuntu is the best Desktop OS
Example:6 Use of Vertical tab in echo Command
jack@nextstep4it:~$ echo -e "Ubuntu \vis \vthe \vbest \vDesktop \vOS" Ubuntu is the best Desktop OS
Example:7 Colored output of echo command
echo command can change the font style, background color of fonts and font colors. Escape sequence \033 can be used to alter font properties. -e option has to be used in order to the escape sequence be in effect. Some of escape codes are listed below :
[0m: Normal
[1m: Bold fonts
[2m: Font color changes to Purple
[4m: Underlined fonts
[7m: Invert foreground and background colors
[8m: Invisible fonts
[9m: Cross lined fonts
[30m: Font color changes to Grey
[31m: Font color changes to Red
[32m: Font color changes to Green
[33m: Font color changes to Brown
[34m: Font color changes to Blue
[35m: Font color changes to Violet
[36m: Font color changes to Sky Blue
[37m: Font color changes to Light Grey
[38m: Font color changes to Black
[40m: Background color changes to Black
[41m: Background color changes to Red
[42m: Background color changes to Green
[43m: Background color changes to Brown
[44m: Background color changes to Blue
[45m: Background color changes to Violet
[46m: Background color changes to Sky Blue
[47m: Background color changes to Light Grey
Below command will print the output in red color.
jack@nextstep4it:~$ echo -e "\033[31mMagic of Linux\033[0m" Magic of Linux
Below Command will print “Magic of Linux” in bold style and red background color.
nextstep4it@nextstep4it:~$ echo -e "\033[1m\033[41mMagic of Linux\033[0m" Magic of Linux
