This tech tip is useful enough to warrant its own post.

If you are updating a DOM element via javascript, for example replacing the content or changing the style, you may notice screen flicker during the update.  Screen flicker on any div update is usually the result of a collision of heights of the elements that are changing.

Be sure that there’s adequate space (or at least no overlap) between the div you are updating and any adjacent divs. The flicker is caused when the DOM renders the new placement & has to ‘adjust’ the overlap.

You may have noticed that I’ve been changing the theme of the site today.

I’ll settle on one I like soon, but this exercise – which I undertake every 3 – 6 months – made me consider why I do this.  It would be easy to say that I simply bore quickly with any given theme & want to try others, but the real reason is more subtle… and vastly more interesting.

I believe that visual cues are a huge part of effective communication.  Experimenting with different themes allows me to see, for myself, the results of these changes. 

No matter your opinion of the political statement these activists were making, you have to respect someone who can literally get blown off the side of a mountain & not lose sight of the objective of the climb.  Pretty amazing stuff.

Tags: greenpeace, mt rushmore, gloabl warming

Yesterday, I encountered an analysis issue that appeared to be resolvable with a simple pattern replacement technique. 

This turned out to be a bit more complex than estimated, as the pattern spanned multiple lines and I struggled to get the regex constructed to match this use case.

I finally figured it out, and although the overall problem remains unresolved (it has many layers), this particular part works well.  My error was in how I viewed use of  /s and /m as mutually exclusive; they aren’t of course, and I have made that mistake one other time over the years.   I also hadn’t set the input record separator ($/) to paragraph read mode.   I’m posting details here to document my specific usage.

Assumptions:

• A literal pattern exists that is present in multiple places in a file
• The literal pattern spans multiple lines in the file
• Literal pattern is
  • Node-path: branches/%%BRANCHES%%
  • Node-kind: dir
  • Node-action: add
• Perl is being used to read the file and current line of file is $line
• Objective is to delete all occurrences of this pattern from the file one $line at a time

Here’s how I did that:

[read the file & crawl thru the lines]

$/ = ”;

$line =~ s/^Node-path:\sbranches\/%%BRANCHES%%.*?^Node-kind:\sdir.*?^Node-action:\sadd.*?//sm;

Tags: perl, regex, tech-tips

Every sys admin needs to quickly free up disk space from time to time, and here are two well-tested scripts I use for exactly this purpose.

The first is a simple command-line use of exec that uses find to construct of list of matching file names, in this case all gzipped tarballs, and then runs the rm command on them.  The curly braces "{}" act as a holder for each file name from the list, and the trailing "\" is used to escape the ";", so that it is passed to find as a literal command terminator.

#find . -name *.tar.gz -exec rm {} \;

You may find (pun intended) that you need a slightly more sophisticated way to construct the list of things to remove.  For example,  to recursively delete all files & directories from an arbitrary depth in the file-system, except for special files or directories.  To accomplish this, I use a small Perl utility I wrote that uses the File::Find module. 

Here is the actual script I use generalized out with a fake $top and /some-pattern-to-exclude/. This script will crawl down (actually the direction that finddepth goes is up) a list of files & directories, and unless the pattern is matched, each file in the directory & then the directory itself is deleted.

How does this work?  Pretty simple – the File::Find module loads some routines, one of which is finddepth. The first argument it expects is a routine to run against all files & directories found, starting at the location named in the second argument.  The wanted routine is run on each element in finddepth’s list & you can use  finddepth’s variables to make your wanted routine smarter.

Tags: tech tips, perl, sysadmin