20030501 Lockergnome Penguin Shell

The History of Commands

As with many GnomeTWEAKS, today we'll talk about a core set of tools that can be customized and used in different ways to tweak the use of your system. These tips fall somewhere between pure core functions and purely individualized use. In other words, the line between the core and the tweak is sometimes a bit blurry.

As you find your level of comfort with the command line, you're likely to run into a need for today's tweak. Honestly, it's amazing how many commands you can execute in a short period of time once you've gained that level of comfort. Often, you'll reuse a command that you've entered only minutes before. That all raises an interesting question. Is there a way to reuse a command without re-entering it keystroke by keystroke?

You probably knew the answer already - of course there's a way. In fact, there are several.

The first is the simplest and the one I use most. The up and down arrows on your keyboard allow you to navigate through the command history preserved by your system. Depending on the distro, your system may record up to 1000 commands. They're all available via the up and down arrows. When you find the command you're looking for, simply press the enter key.

One of the core tools of your Linux system is the history app. Executing this file with:

history

will display a list of all commands up to a pre-determined maximum. As noted, many systems record up to 1000 commands, so this list may be very long. As much as anything else, it's interesting in its bare form - that is, without options. You'll probably find yourself surprised by just how many commands you've entered.

If the command you need is a few hours old, it's likely to be more effort than necessary to arrow back through all the recorded commands. And, as you've seen, the history command is more for interest than utility without options. In that instance, a combination of command connected by a simple pipe will do the trick:

history | grep .ipk

This command executes the history app then pipes the results through grep to find the string ".ipk". This will display all the commands I've entered that relate to Zaurus-packaged files - .ipks.

Your system is recording a history of your commands. That's not a bad thing. In fact, as you master the command line, you'll rely more and more on the command history tools to ease your keystroke load.

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Reading Permissions

Let's take a run back through one of the most basic elements of your Linux system - reading the permissions set on your files.

We'll start with a fairly simple concept in Linux. Every file has a set of permissions that allow or disallow specific uses. These permissions are:

r - read
w - write
x - execute

Starting with these simple permissions, Linux adds a layer of granularity by further breaking these permissions out into three more level:

user - normally the owner of a file and always root by default
group - a convenient way to cluster multiple users together
others - anyone not covered by user or group

You've now got six elements in permissions, each of which can be used with any other. For instance, permissions can be set on a file that allow the user and group to read, write and execute, but others only to read. Or, perhaps the group and others can read and write, but only the user can execute. Once you start unrolling the combinations, the possibilities for permissions on your system begin to look incredibly flexible.

So, how do you know how the permissions are set on a particular file?

ls -l file

From the command line, this provides a [l]i[s]t in the [l]ong form of the file attributes. You'll see something similar to this:

-rw-rw-r-- 1 tony tony 975155 Apr 24 23:30 wetlands.mp3

This line shows everything you need to know about the permissions on the file. Remember that three file-oriented permissions exist - rwx - read, write and execute. In the first cluster of letters in the above line, the first position (-) denotes the file type. If this file was a directory, the - would be replaced by a d.

Next, to the right, is the first trio of permissions. This set of three characters represents the permissions for the user: rw-. In other words, the owner of the file may read and write.

The next group of three is the permission for the group. In this case, they're the same. Anyone within the group can also read and write the file.

Finally, you'll find the others permissions. This is often referred to as "the world" because it's everyone not covered by user or group. And, once again, the world can read and write this particular file.

The first name shown in the ls -l command is the owner of the file - the user. The second is the name of the group. If, for instance, dave was a member of the tony group, the dave user would also have read and write permissions on the file.

Finally, the line ends with data about the file itself. This includes size, creation time and name.

If, for some reason, you're unable to execute, read or write to a file, check the permissions using the ls -l command. It's a Linux core tool.

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Softball Stats 1.2 Stable

http://softballstats.sourceforge.net/

"SoftballStats is a collection of PHP scripts and a MySQL database that track the stats, games, players, and every play made in multiple softball/baseball seasons. It also compiles statistics for each player. There two groups of scripts, stat scripts (which display stats, player info, and game info for the current season) and admin scripts (through which the Stat Master enters the season info, game info, player info, and every play made in all games)."

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Nohup Helper
Scribbled by Paul Johnston

"After reading the issue I wanted to respond that I too had found that same very fruitful command (nohup) about 6 months ago but I use it on our UNIX server. It is great that you are sharing this information. I too , found it difficult to run processes in the background when logging out of the console window. That's when I found 'NOHUP'.

"I would like to add, that depending on the process that is run in the background it may require it's output piped to a file. So I have coded it as

nohup gkrellm & > gkrellm.out &

"The gkrellm.out will reside in the directory that the nohup command is executed unless you qualify the output file with a directory.

"Hope this information is useful to others."

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The Linux Documentation Project

http://www.tldp.org/

"The Linux Documentation Project (LDP) is working on developing good, reliable documentation for the Linux operating system. The overall goal of the LDP is to collaborate in taking care of all of the issues of Linux documentation, ranging from online documentation (man pages, HTML, and so on) to printed manuals covering topics such as installing, using, and running Linux. Here is the Linux Documentation Project Manifesto and Copyright License for LDP works."

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