We are transliterating the Greek letters into English as follows:

Greek	English
α	a
β	b
γ	g
δ	d
ε	e
ζ	z
η	e
θ	th
ι	i
κ	k
λ	l
μ	m
ν	n
ξ	x
ο	o
π	p
ρ	r
σ	s
ς	s
τ	t
υ	u
φ	ph
χ	ch
ψ	ps
ω	o

Linux shell script for transliteration into English
Prior to running the below script, the Greek Text must first have all the accent marks removed and then be converted into lower case letters.

sed -i 's/α/a/g' file.txt
sed -i 's/β/b/g' file.txt
sed -i 's/γ/g/g' file.txt
sed -i 's/δ/d/g' file.txt
sed -i 's/ε/e/g' file.txt
sed -i 's/ζ/z/g' file.txt
sed -i 's/η/e/g' file.txt
sed -i 's/θ/th/g' file.txt
sed -i 's/ι/i/g' file.txt
sed -i 's/κ/k/g' file.txt
sed -i 's/λ/l/g' file.txt
sed -i 's/μ/m/g' file.txt
sed -i 's/ν/n/g' file.txt
sed -i 's/ξ/x/g' file.txt
sed -i 's/ο/o/g' file.txt
sed -i 's/π/p/g' file.txt
sed -i 's/ρ/r/g' file.txt
sed -i 's/σ/s/g' file.txt
sed -i 's/ς/s/g' file.txt
sed -i 's/τ/t/g' file.txt
sed -i 's/υ/u/g' file.txt
sed -i 's/φ/ph/g' file.txt
sed -i 's/χ/ch/g' file.txt
sed -i 's/ψ/ps/g' file.txt
sed -i 's/ω/o/g' file.txt