"Generic plotting tools available in the unix toolbox"
is probably every basic Un*x tool, you need to combine tools to create things. I love to combine Latex, R and Sweave! The term "logs"
leaves the question a bit open but apparently by purpose, notice the term "generic"
. So nothing about pre-processing with AWK/SED/etc and only about plotting coming in text-files. Have fun!

$ mkdir Pictures
$ R CMD Sweave paper.Rnw
Writing to file paper.tex
Processing code chunks with options ...
1 : term verbatim
You can now run (pdf)latex on 'paper.tex'
$ pdflatex paper.tex 3&>/dev/null
$ evince paper.pdf
paper.tex
$ cat paper.tex
\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{graphicx}
\usepackage[T1]{fontenc} % intended quotes
\begin{document}
\sloppy
<<echo=FALSE>>=
png('./Pictures/examples.png')
x<-1:10
y<-10:1
par(mfrow=c(2,2))
# Demand/Supply example
plot(x,y-2, type='l', ylab='Price', xlab="Quantity")
lines(y,x+2)
lines(x,x)
title(main="Examples by HHH for R Sweave Latex")
hist(rnorm(100)) # histogram example
plot(sin(1:1E3),cos(1:1E3)) # circle example
plot(sin(1:1E3),1:1E3) # sin example
@
\includegraphics{./Pictures/examples.png}
\end{document}
Now the next puzzle is accessibility (supposing the op wants ASCII output, not just generic tool). Sorry I do not yet have an answer for it but I will list below info for further exploration.
Just thinking aloud: choose raster image format such as TIFF and then just print evevery 100th column or s/thing like that to see it. Sorry just speculating but I know that TIFF is a de facto raster image format for all kind of archival purposes -- I do not know yet exactly how the OCR engines, such as Tesseract, handle them but but here the problem is easy because you can skip a lot of stuff in the preprocessing of the image -- because we do know how R generates them. Someone got an idea how do this? Or am I reinventing the wheel? At the simplest, pick out a tool that generates hings to ASCII, a bit restrictive to be "generic"
.
Related
- Which tools for ASCII portfolio visualization?