One of the things that makes Linux and Unix-like systems both powerful and frustrating is that there are many ways to accomplish any particular goal. Take something simple like running a bunch of commands in sequence as an example. The obvious way is to write a shell script which offers a tremendous amount of flexibility. But what if you just want some set of commands to run? It sounds simple, but there are a lot of ways to issue a sequence of commands ranging from just typing them in, to scheduling them, to monitoring them the way a mainframe computer might monitor batch jobs.
Let’s jump in and take a look at a few ways you can execute sequences from bash (and many other Linux shells). This is cover the
at commands along with a batch processing system called task spooler. Like most things in Linux, this isn’t even close to a complete list, but it should give you some ideas on ways to control sequences of execution.
Continue reading “Linux-Fu: Running Commands”
[Don] and his wife were looking for a way to teach their two-year old daughter how to tell time. She understood the difference between day and night, but she wasn’t old enough to really comprehend telling the actual time. [Don’s] solution was to simplify the problem by breaking time down into colored chunks representing different tasks or activities. For example, if the clock is yellow that might indicate that it’s time to play. If it’s purple, then it’s time to clean up your room.
[Don] started with a small, battery operated $10 clock from a local retailer. The simple clock had a digital readout with some spare room inside the case for extra components. It was also heavy enough to stay put on the counter or on a shelf. Don opened up the clock and got to work with his Dremel to free up some extra space. He then added a ShiftBrite module as a back light. The ShiftBrite is a high-brightness LED module that is controllable via Serial. This allows [Don] to set the back light to any color he wants.
[Don] already had a Raspberry Pi running his DIY baby monitor, so he opted to just hijack the same device to control the ShiftBrite. [Don] started out using a Hive13 GitHub repo to control the LED, but he found that it wasn’t suitable for this project. He ended up forking the project and altering it. His alterations allow him to set specific colors and then exit the program by typing a single command into the command line.
The color of the ShiftBrite is changed according to a schedule defined in the system’s crontab. [Don] installed Minicron, which provides a nice web interface to make it more pleasant to alter the cron job’s on the system. Now [Don] can easily adjust his daughter’s schedule via web page as needed.
It’s no secret that the central US is feels like a very humid oven right now. [Erik’s] window AC hack might help you out if you’re coping with triple-digit temperatures. He added network connectivity to the unit above but the picture is a bit deceiving. The blue CAT-5 cable that enters the bottom isn’t connecting directly to the network, but extends the up and down button connections for the unit to an external relay board. From there he uses an SNMP board to connect it to the network and uses PHP commands to reset the temperature. The unit has a working range of 66-88 degrees Fahrenheit so he cycles enough button press to reach the maximum or minimum level, then sets the desired temperature (avoiding the need to know what temperature the unit is currently set at).
If you’ve got an AC unit with a remote control you could always use an IR device to patch into the system for similar functionality.