~$ sudo iwlist wlo1 scanning | python3 -c '

import re,sys

def tokenize(code):
    token_specification = [
        ("CELL",  r"^\s+Cell \d+"),
        ("FREQ",  r"^\s+Frequency:(\d+(\.\d*)?)"),
        ("CHNL",  r"^\s+Channel:(\d+)"),
        ("ESSID", r"^\s+ESSID:\"([- A-Za-z0-9$@^`,|%;.~()/\\{}:?[\]=+_#!]*)\""),
        ("LEVEL", r"\s+Signal level=(-\d+)"),
    ]
    tok_regex = "|".join("(?P<%s>%s)" % pair for pair in token_specification)

    for mo in re.finditer(tok_regex, code, re.M):
        typ = mo.lastgroup
        if typ == "CELL":
            if "res" in vars() and res:
                yield res
            res = {}
        else:
            grs = [v for v in mo.groups() if v not in [mo.group(typ), None]]
            assert len(grs), "Forgot capture value for %s ?" % typ
            res[typ] = grs[0]
    if res:
        yield res

data = list(tokenize(sys.stdin.read()))

print(
"""
# legend
set key top left outside horizontal
set xlabel "Channel"
set ylabel "Strength (dbm)"
# x axis step
set xtics 1
# show horizontal grid lines 
set grid ytics
set xrange [-2:16]
set yrange [%(bottom)d - 0.1:%(top)d]
set term png truecolor size 1280,720
plot for [IDX=0:%(total)d-1] "-" \
    using 2:(%(bottom)d):(4):(2*abs(%(bottom)d - $1)) \
    title columnheader(1) with ellipses \
    fill transparent solid 0.5 
""" 
% {
    "total": len(data), 
    "top": max([int(tok["LEVEL"]) for tok in data]) + 1, 
    "bottom": min([int(tok["LEVEL"]) for tok in data]) - 5, 
})

for tok in data:
    print("\"%s\"" % (tok["ESSID"] or "<HIDDEN>"))
    print(tok["LEVEL"], tok["CHNL"])
    print("e")
    assert set(("FREQ","CHNL","ESSID", "LEVEL")) <= set(tok)
' | gnuplot > out.png

~$ gnuplot --version
gnuplot 4.6 patchlevel 6
~$ echo '
plot for [IDX=0:1] "-" using 1:2 title columnheader(1) with lines
hello
1 1
3 3
e
world
1 3
3 1
e
' | gnuplot -p

~$ echo '
set term png truecolor size 1280,480
set xrange [0:6]
plot for [IDX=0:3] "-" using 2:1 title columnheader(1) with points pointsize 3
"Anna"
-93 1
e
"Erika"
-73 1
e
"Alina"
-84 1
e
"Nast"
-93 5
e
' | gnuplot > wifi.points.png

~$ echo '
set term png truecolor size 1280,480
set xlabel "Channel"
set ylabel "Strength (dbm)"
set xrange [0:6]
set yrange [-110:-60]
set grid ytics
plot for [IDX=0:3] "-" using 2:1:(2):(abs($1/3)) title columnheader(1) with ellipses
"Anna"
-93 1
e
"Erika"
-73 1
e
"Alina"
-84 1
e
"Nast"
-93 5
e
' | gnuplot > wifi.ellipses.png