[Linux] Single quote vs. Double quote inside Shell script

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.

Reference

1. Hack 87. Single Quote and Double Quote Inside Shell Script

转载于:https://www.cnblogs.com/unimous/archive/2012/10/16/2725702.html