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Groovy Template is a templating engine for JavaScript. It lets you insert dynamic content into any text through the use of templates. A template contains variables and/or expressions, which get replaced with values when a template is rendered. This is very similar to JSP markup. 

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<%= issue.getKey() %>

For single-statement expressions, you can also use the following shortcut:

${issue.getKey()}

To simply execute a Groovy code and not output the result, write your Groovy code as <% some Groovy code %>. For example:

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$currentUser returns an ApplicationUser

$currentUser.name returns the username of the current user

To call a method on the variable, use ${variable.method()}:

${currentUser.getName()} also returns the username of the current user

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Issue key: $issue.key${issue.get("issuekey")}

Comment an issue based on the priority of the issue:

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To send an Email to the Voters and Watchers of the issue when the issue is resolved, write this as the Subject of the Email (note that we mixed <%= %> and ${} expressions only to show how both are valid):

Hi All,
<% if (issue.assignee)
{%>
The issue <%= issue.key%> has been resolved by <%=issue.assignee.displayName%>
<%}
else
{%>
The issue $issue${issue.key} has been resolved
<%}%>
Regards,
<%=issue.get("project")?.getLead()?.getDisplayName()%>

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