While I was writing my last Mythbusters blog post, I realized that it’d be really useful to have a “quick and dirty” plotting program — one that just takes the output of another program and plots it, no questions asked. Actually, let me rephrase that: I knew it would be useful, it just never occurred to me that I don’t have one. Most of the common plotting programs people tend to use, like GNUplot, expect to be configured with the format and syntax and display options and all that junk that you don’t really care about when you just want to turn numbers into a picture.

If you have GNUplot installed, here’s a little script to do just that:

#!/bin/bash

using=""

shopt -s extglob
if [[ "$1" == +([[:digit:]])*(,+([[:digit:]])) ]]; then
        using="using ${1//,/:} "
        shift
fi
shopt -u extglob

plotopts=""

if [[ "$*" == *title* ]]; then
        next_is_title=""
        for word; do
                if [[ -n "$next_is_title" ]]; then
                        plotopts="$plotopts title '$word'"
                        next_is_title=""
                        continue
                fi
                if [[ "$word" == "title" ]]; then
                        next_is_title="1"
                else
                        plotopts="$plotopts $word"
                fi
        done
else
        plotopts="$* title 'STDIN'"
fi

gnuplot -p -e "plot '-' ${using}${plotopts}"

Save it as plot, make it executable, and put it in your $PATH, and then you can …

Bash, the shell commonly found on modern Linux systems, has a well-deserved reputation for being a tremendously complicated piece of software. The man page is more than three thousand lines long — what for most other programs would be the “pocket reference manual” is in this case more like a hundred-page book! But it’s everywhere, so if you want to do shell scripting, you have to know Bash. (To be fair, other shells can be even weirder) I’ve been working with this shell for a long time, and over the years I’ve come to terms with most of its wacky features: parameter expansion, quoting, variable substitution, job control, arrays, here strings, arithmetic evaluation, signal handling, and more. But I have never been able to understand I/O redirection.

Until now.

Now, I’m not talking about the basics. Of course I knew how to use the simple examples; for instance, I learned early on that

command >output.txt >errput.txt

means that anything the command prints to its standard output stream winds up in output.txt and anything it prints to its standard error winds up in errput.txt. I know that you can “merge” standard output and …