Extract [a-c] from file and save in another file

Question

I have a file with alphabetically sorted lines. The file starts from 0-9 till a-z. Example

000dasd
001dss
awer
addd
alko
babb
bobb
...
zzasd

Since the file is really big I want to divide it into multiple files where in each file I will store different blocks - one file that will contain all lines starting with 0-9, one file containing [a-d], one file containing [e-h], and so on.

Currently, I have a grep command which does this but for just one char. Since I'm really new in Linux, grep, awk, and shell scripting I can use some help here.

That's how I do it for all lines that are starting with 'a'

grep "^[[:blank:]]*a" file.txt > a-file.txt

Answer 1

You can use [] to enclose a range of characters so [0-9] would match all arabic digits, [a-d] would match the letters a, b, c and d etc.

So you could run

grep "^[0-9]" file.txt > digit-file.txt
grep "^[a-d]" file.txt > a-d-file.txt

etc