Command-Line – New Commands

The more basic a command is, the more likely it is to predate Linux. The long history of commands is an advantage in that core commands have had more than four decades to get the bugs out and to make revisions as the expectations and needs of Linux users have evolved. However, more options can also make mastering commands more difficult. At times, all the revisions can make learning and remembering commands absolutely cumbersome.

Rather than completely restructure basic commands, Linux programmers have often responded by writing completely new commands that are either rationalizations or simplified front ends for older commands. Being as set in my ways as most people, initially, I have often been skeptical of these new commands. Yet when I tally them up, I find that I have replaced standard commands with newer ones in a surprising number of cases. Here are seven leading examples.

tree

Few commands are as basic as ls. When working from the command line, you can use it a dozen times in an hour to list the contents of a directory.

tree (Figure 1), which replaces ls, shares many of the same options, but with one important difference: tree displays the contents of a directory in a tree view, similar to the one in a file manager. That may sound like a minor difference, but a visualization is always welcome, especially in these desktop-oriented days.

Figure 1: tree improves on ls by offering a graphical view of the directory tree.

By default, tree displays the current directory. However, you can also specify a top directory after the command options. Usefully, archived files are treated as directories, so their content can be viewed directly and without another command.

If you want more information, you can set tree to list file attributes and include hidden files. If you want less, you can show only directories and omit blank directories. Essentially, tree does everything ls does – even color-coding by setting color-coding variables – while also providing an additional bag of small enhancements.

multitail

tail is a standard command used by administrators to keep an eye on the most recent lines in logs and other files that change frequently. As the name implies, its replacement multitail (Figure 2) allows multiple files to be monitored with the same command, saving both effort and system resources.

Figure 2: multitail (Figure 2) displays the bottom output from multiple files.

Like tail, multitail can set the number of lines to display, as well as the interval between samples. In addition, multitail can be set to mark set intervals in which nothing happened with an x, or to replace repetitions of the same line with a message stating how many times it has been repeated. Similarly, multitail includes options for which windows present the output, including the option to merge all output from all files in the same window. Windows that are inactive for a defined interval can be set to close automatically, and output can be sent to a file or to another command.

One especially useful feature is the ability to use regular expressions. When regular expressions are defined, an entire directory can be monitored at the same time, with messages appearing only when a file has changed. Color and column formatting options are also available – all of which is considerably more sophisticated than tail with its handful of commands.

pax

Over the years, Linux has accumulated a bewildering set of formats for file compression (bzip2, gzip, tar, etc.). Each format has its own options, although some are more closely related than others. The pax command cuts through this confusion by offering a single interface for over half a dozen formats (Figure 3). The main difficulty is that while some formats like tar use the option -x FORMAT, other formats like bzip2 have their own options, probably because support for them was added afterwards. Most users, too, will be surprised to learn that there are three different tar formats from which to chose. However, because format is only one option among others, pax spares users having to scan man pages when dealing with unfamiliar formats.

Figure 3: pax provides a front end for multiple archive formats.

pax's other options are not as complete as those for single format commands, but they are adequate enough for most purposes. Files can be appended to existing archives, and the contents of an archive can be defined by several criteria, such as file or block sizes, or a range of dates to include or exclude. Other options specify what file attributes to use. Overall, pax is a major simplification of archiving options.