robobait

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How to update the JRE in LiClipse

Posted by on 28 May 2021 | Tagged as: robobait, software engineering, technical support

I use the LiClipse software development environment (IDE) for most of my software development. It is a distribution of the Eclipse Project IDE, with PyDev, and its own Java runtime environment (JRE), and some extras. I like it because I can, by installing more components, work with more software languages. Most of the time, one can update the various components of an Eclipse IDE using the internal “Check for Updates” function. However, my installation had reached the point where updating the components required upgrading the JRE. The documentation for the latter upgrade was inadequate. Here is what I figured out. It worked for me. I hope these instructions are helpful for others.

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How to fix table contents turned to “0” in LibreOffice

Posted by on 30 Apr 2021 | Tagged as: robobait, software engineering, technical support, web technology

Well, that was a fright. I was editing a large report with the LibreOffice word processor. I had a table of results. It consisted of a placeholder table — a header and a couple of rows — with Table Styles applied to get the rows formatted right. I pasted in dozens of rows of content from a spreadsheet. I saved the file for the night. The next morning, I opened the document, and to my horror, found that text values in many of the columns had been turned to “0”. This is LibreOffice bug 131025. And here is how I recovered from the error, and got my table contents back. I hopes it helps others who encounter this bug.

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How to change and delete attributes in an XML file using XSLT

Posted by on 31 Mar 2021 | Tagged as: robobait, software engineering

I recently had a need to modify a large XML file by changing attributes of one kind of element — changing the value of a certain attribute, and deleting another attribute — while preserving everything else: element text, surrounding elements, etc. I did not readily find code for modifying an attribute value in my searches. Here is what worked for me. Perhaps it will be helpful for someone else.

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How to use XSLT to modify XML files inside .ODT documents

Posted by on 31 Jan 2021 | Tagged as: robobait, technical support, Uncategorized

The .ODT word processor documents produced by LibreOffice and Apache OpenOffice are in fact ZIP archives consisting of XML files, other files, and directories. It is actually straightforward to crack open the archive and get at the files and directories within. To edit the XML files, or just to explore them, XSL Transformations (XSLT) are a useful tool. This is a look at how to use XSLT and the xsltproc tool on XML files extracted from .ODT documents.

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How to crack open LibreOffice .ODT documents for fun and bug fixing

Posted by on 31 Dec 2020 | Tagged as: robobait, technical support

The .ODT word processor documents produced by LibreOffice and Apache OpenOffice are in fact ZIP archives consisting of XML files, other files, and directories. It is actually straightforward to crack open the archive and get at the files and directories within. This can be helpful for fixing bugs, or just for exploring. I recently had cause to do just that. Here is how to open up .ODT documents, and then turn those files and directories back into a document file.

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Link from Trac to GitHub using changeset links

Posted by on 30 Sep 2020 | Tagged as: robobait, software engineering, web technology

There is an elegant way to link from the wiki and bug tracker called Trac to GitHub by means of changeset links. Unfortunately, Trac’s documentation on WikiFormatting and on TracLinks does not currently describe this. But one project which I use, MacPorts, uses Trac to track MacPorts bugs and to host wiki documentation. They prefer that contributors use these changeset links rather than URLs when referring to MacPorts on GitHub. So, this is the documentation for these changeset links, in a form which I wish was in the main Trac documentation. It is here to remind me. Maybe it will also help others searching for how to do this.

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PostScript code converting UTF-8 to UTF-16

Posted by on 31 Aug 2020 | Tagged as: robobait, software engineering, Unicode

This is a little bit of code which was fun and nostalgic to write, even though the motivating project fell through. I wrote PostScript language functions to convert strings with UTF-8 contents, into strings with UTF-16 contents. This was intended to be part of a batch tool to convert PDF documents to PDF/A format, but that did not work out. However, the code works, and here it is.

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Concise Time Machine logs on macOS 10.13 High Sierra

Posted by on 31 Jul 2020 | Tagged as: mac, robobait

I’m concerned that Time Machine is taking so long to back up my laptop to my file server, that it may be the sign of a problem with my file server. The first step in investigating a problem like this is to get data. I think I have found a way to get useful log data about Time Machine backups, using the log show command or the Consolation3 application. I’d like to share how I do it.

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Resolving “log archive metadata is missing” and “error number 65”

Posted by on 30 Jun 2020 | Tagged as: robobait

On macOS 10.13 High Sierra, one way to diagnose Time Machine slowdowns and other problems is to use the log shell command. Unfortunately, on my system I sometimes get an error:

% log show --last 2s --style syslog
log: warning: The log archive contains partial or missing metadata
log: cannot use --last when archive metadata is missing

This appears to prevent me from using the --last option to limit output to the most recent time interval. The failed log command returns an exit status of 65, which we can see using echo $? :

% echo $?
65

For the benefit of web searchers, here is what I have found out about how to resolve this error message. Warning: it won’t be a fix, but I do have workaround.

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FFmpeg’s fps filter, documented

Posted by on 30 Apr 2020 | Tagged as: FFmpeg, robobait, software engineering, web technology

The FFmpeg media editing software is a valuable tool, but its documentation is only barely adequate. It certainly does not answer all the questions I have, as a user trying to understand why FFmpeg is not doing what I want it to do.

Fortunately, FFmpeg is open source, so when the documentation fails, one can read the source. I wanted to learn about presentation time stamps and time bases. The fps video filter source code, in file libavfilter/vf_fps.c, was an instructive read.

I took what I learned from reading that source, and did a complete rewrite of the fps filter documentation. It is longer than the original fps filter documentation (as archived in April 2020 — you can check if the present documentation is any better). I believe the rewrite is more complete and more accurate. I contributed the rewrite to the FFmpeg project. I submitted it as a patch to the ffmpeg developers list. Discussion continues. I don’t know if this contribution will ultimately get accepted.

So, for the benefit of FFmpeg users who are web-searching for answers, here is my documentation of FFmpeg’s fps video filter.

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