Charly's Column – moreutils

In the March 2013 issue, I wrote about ifdata, which gives you information about networks in a way that is great for scripting. I had taken the tool from the moreutils package at the time; this toolbox comes with almost every flavor of Linux, and, if not, you can download it [1]. Further investigation of the package reveals even more laser-sharp tools. For instance, combine is really practical for comparing stuff. You need to pass in the names of two text files and a logical operator: and, not, or, or xor (exclusive or).

As an example, I created two text files with IP addresses and networks. Some of the addresses and networks are included in both files, while others are not. Now I let combine compare the files, first with the and operator:

combine iplist-a.text and iplist-b.text

In Figure 1, you can see the content of the two files, and then the combine command line. The output I got was all the lines that occur in both files.

Figure 1: The contents of two sample files at the top. combine compares them in different ways.

When I executed the command with the or operator, I could see everything that occurred in one or both the files. Important: If a line appears in both files, it also appears twice. This is often undesirable, but can be suppressed with:

combine iplist-a.text or iplist-b.text | sort | uniq

One thing is probably already clear to most readers: The same results are possible with cat, but many roads lead to Rome. Using the not operator, I can output all the lines that occur in the first file, but not in the second. The xor operator tells combine to return the lines that are only found in one file, but not in both.

Sly List

Another workhorse from the moreutils package goes by the name of vidir. I don't use it often, but if I do, it saves a huge amount of typing. (Praise be to anything that contributes to my laziness.) vidir in particular makes it easier to rename files. Normally, I do this with:

mv <File_1> <File_2>

The Perl rename tool does this more conveniently and can process multiple files at the same time. But vidir has a special trick up its sleeve. When I run it in the current directory, it opens Vi (or whatever $EDITOR defines) and displays a list of the files present in the directory. Now I can edit the file names to suit my needs. In Figure 2, I renamed the iplist files from the earlier example. When I leave the editor and run ls, hey presto, I find the files have been renamed.

Figure 2: vidir fetches a file list and presents it in the editor.

This excursion has by no means exhausted the moreutils box – in fact, it comprises 17 tools. Some only do tiny jobs (e.g., isutf8 checks whether a file is valid UTF-8); others are more extensive – some great DIY stuff included!