Revision [1064]
This is an old revision of CommandTie made by DavidLee on 2009-11-29 08:29:30.
Command tie
Name
tie Ties an xquery expression to a variable for ease of accessSynopsis
tie variable expressionDescription
Tie associates an xquery expression to a variable so it can be queried more with a simplier syntax.The expression is any xquery expression and should be quoted or escaped. The expression is evaluated whenever the variable is accessed with either
the syntax
${variable:arg}or
${variable[index]:arg}In the first case, the variable becomes context node for the xquery, and must be a single Item (may not be a sequence).
In the second case the variable is treated as a sequence, and the index'd element (1 based) is used as the context item.
In both cases, the text following the : is treated as a string and assigned to the $_ variable.
Examples
tie is very useful to access property or map like xml data.
For example, create a property object using xproperties
A=$<( xproperties -a a="A value" -a b="B value") xecho $A
Results
<properties version="1.0">
<entry key="b">B value</entry>
<entry key="a">A value</entry>
</properties>
<entry key="b">B value</entry>
<entry key="a">A value</entry>
</properties>
Now tie the variable A
tie A './/entry[@key = $_ ]/string()'
Now properties can be referenced by key value and returned as strings
echo ${A:a}Result
A value
Compare this to the equivalent expression needed to extract a property value
echo <[ $A//entry[@key="a"]/string() ]>
Notes
Tied variables survive resetting of the variable, so you can update variables and the tied expression is maintained.
Unlike the <[ ]> syntax, the tied xquery does NOT have access to the shell variables.
Commands
CategoryCommands
