Articles, notes and random thoughts on Software Development and Technology
Just as the dd command can be used to create a disk image of an SD card on the Mac (see here), you can use dd to write a downloaded (or backup) disk image to an SD card too:
sudo dd of=/dev/rdiskx if=/path/to/image bs=1m
where x is the disk number as shown by diskutils list.
Given that SD cards have a limited lifetime for writes, using an SD card for a harddrive for Pi may not be the smartest idea in terms of reliability or longevity, so asking how you back up your SD card is a good question. There’s some good answers here.
Specifically on the Mac, find out the disk number of the attached sd card with :
diskutil list
then use the dd command:
dd if=/dev/rdiskx of=/path/to/image bs=1mwhere x is the disk number listed from diskutil.
pass-by-value: expressions as arguments to a function are evaluated once on passing to the function
pass-by-name: expressions are evaluated only when referenced, if they are not referenced they are not evaluated, and the expression is evaluated every time the expression is referenced
System.out.println("Calling squareCallByValue(): ")
squareCallByValue( doSomething() )
System.out.println("nCalling squareCallByName(): ")
squareCallByName( doSomething() )
System.out.println("nCalling callByNameNoReference(): ")
callByNameNoReference( doSomething() )
def doSomething() : Int = {
System.out.println("doSomething() called")
2
}
def squareCallByName(x: => Int) = {
var result = x * x
System.out.println("x in squareCallByName: " + result)
}
def callByNameNoReference(x: => Int) = {
}
def squareCallByValue(x: Int) = {
var result = x * x
System.out.println("x in squareCallByValue: " + result)
}
A few notes for a few common JSTL things so I don’t forget:
taglibs:
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %> <%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %>
Conditionals:
<c:choose> <c:when test=””> </c:when> <!--other when conditions --> <c:otherwise> </c:otherwise> </c:choose>
String replace using replace function:
${fn:replace(foo, '"', '\"')}
This next tip for using a loop varStatus to build HTML ids is from: http://stackoverflow.com/questions/6600738/use-jstl-foreach-loops-varstatus-as-an-id
<c:forEach items="${loopableObject}" var="theObject" varStatus="theCount">
<div id="divIDNo${theCount}">
</div>
</c:forEach>
This unexpectedly gives:
<div id="divIDNojavax.servlet.jsp.jstl.core.LoopTagSupport$1Status@5570e2">
To get the actual varStatus id you need to use:
${theCount.index} gives value from 0
${theCount.count} gives value from 1
For example:
<div id="divIDNo${theCount.index}">