Linux Journal - September 2011

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What Day Is It?

I’m sending a little feedback to Dave Taylor’s “parsing the cal” output (see Dave’s column in the June–September 2011 issues). There’s no need to use regular expressions in the awk script at all, because you can compare numbers directly. Below, you’ll find the script you can call by the following command line:

cal | awk -f day.awk 25

day.awk BEGIN{ ARGC=1; getline;getline; for(i=1;i<=NF;i++) wd[i]=$i } {for(i=1;i<=NF;i++) if($i==ARGV[1]) print wd[i+($0~/^ /?(7-NF):0)] }

In the BEGIN block, ARGC=1 prevents it from taking the last argument ( 25 in this case) as an input file. Then, the script fetches the first two lines and stores the weekday names in an array.

The rest of the script compares the argument number with every field in every line. On a match, the day name is output, wd[i]. The month does not always start on a Sunday, so the script has to fix the index for lines starting with a space (condition $0~/^ /). For those lines, the first item starts with

index 7-NF. Note that this fix also works fine for the second line of numbers (which also starts with a space), since 7-7 equals 0.

You can make the script a one-liner if you like. It was written in multiple lines for readability reasons. And, last but not least: great OS, great magazine, keep going.

—Eric Miller

Dave Taylor replies: Thanks for your note. I realized that there was a way to break down the input and process it with a multiline awk script (just as I could do much of the task more easily in Perl or, for that matter, a short C program), but my goal with the Work the Shell column is to force myself to stick with standard Linux shell commands and capabilities as much as possible and see what I can accomplish. Sometimes the result is a bit, um, Byzantine and unquestionably inefficient, but the upside is that it’s always interesting and, I hope, informative and entertaining reading.

Installfest 2001

Installfest goal: adapt seven older desktop computers for use by fourth-grade teacher Mike Steins at Shenandoah St. Elementary School and learn how to install/configure Linux. (We had two Linux experts in the group.)