Hack 87. Single Quote and Double Quote Inside Shell Script

by Ramesh

Let us review how to use single quote and double quote inside a shell script.

Following example displays an echo statement without any special character.

$ echo The Geek Stuff
The Geek Stuff

Echo statement with a special character ; . semi-colon is a command terminator in bash. In the following example, “The Geek” works for the echo and “Stuff” is treated as a separate Linux command and gives command not found.

$ echo The Geek; Stuff
The Geek
-bash: Stuff: command not found

To avoid this you can add a \ in front of semi-colon, which will remove the special meaning of semi-colon and just print it as shown below.

$ echo The Geek\; Stuff
The Geek; Stuff

Single Quote

Use single quote when you want to literally print everything inside the single quote. Even the special variables such as $HOSTNAME will be print as $HOSTNAME instead of printing the name of the Linux host.

$ echo 'Hostname=$HOSTNAME ;  Current User=`whoami` ; Message=\$ is USD'
 
Hostname=$HOSTNAME ;  Current User=`whoami` ; Message=\$ is USD

Double Quote

Use double quotes when you want to display the real meaning of special variables.

$ echo "Hostname=$HOSTNAME ;  Current User=`whoami` ; Message=\$ is USD"
 
Hostname=dev-db ;  Current User=ramesh ; Message=$ is USD

Double quotes will remove the special meaning of all characters except the following:

• $ Parameter Substitution.
• ` Backquotes
• \$ Literal Dollar Sign.
• \´ Literal Backquote.
• \” Embedded Doublequote.
• \ Embedded Backslashes.