fretl

   9      8      7      6      5      4      3      2      1      0
+--.-------------.-------------.-------------.------------------+
|--C#--|------|--B---|------|--A---|--G#--|------|--F#--|------|| E
|--G#--|------|--F#--|------|--E---|------|--D---|--C#--|------|| B
|--F#--|------|--E---|------|--D---|--C#--|------|--B---|------|| A
|--C#--|------|--B---|------|--A---|--G#--|------|--F#--|------|| E
|--F#--|------|--E---|------|--D---|--C#--|------|--B---|------|| A
|--B---|------|--A---|--G#--|------|--F#--|------|--E---|------|| D
+--.-------------.-------------.-------------.------------------+

fretl is a command-line fretboard specifically designed for mirrored (a.k.a. left-handed) guitars.

Unlike most fretboard diagrams you can found online, fretl

1. Supports mirrored guitar, since some misfortuned ones learned to reason about notes on guitar the opposite way.
2. Has first-class support for alternative tunings
3. Has no assumption about how many strings a guitar should have
4. Uses unambiguous representation of notes, intervals, and scales, so it can distinguish enharmonic equivalent notes such as C# and Db.

For example, you could print the notes in A major scale in DAEAC#E tuning up to 7th fret by

$ fretl -f7 -rA DAEAC#E < scales/major
   7      6      5      4      3      2      1      0
+--.-------------.-------------.------------------+
|--B---|------|--A---|--G#--|------|--F#--|------|| E
|--G#--|------|--F#--|------|--E---|------|--D---|| C#
|--E---|------|--D---|--C#--|------|--B---|------|| A
|--B---|------|--A---|--G#--|------|--F#--|------|| E
|--E---|------|--D---|--C#--|------|--B---|------|| A
|--A---|--G#--|------|--F#--|------|--E---|------|| D
+--.-------------.-------------.------------------+

or alternatively display in scale degrees.

$ fretl -d -f7 -rA DAEAC#E < scales/major
   7      6      5      4      3      2      1      0
+--.-------------.-------------.------------------+
|--2---|------|--1---|--7---|------|--6---|------|| 5
|--7---|------|--6---|------|--5---|------|--4---|| 3
|--5---|------|--4---|--3---|------|--2---|------|| 1
|--2---|------|--1---|--7---|------|--6---|------|| 5
|--5---|------|--4---|--3---|------|--2---|------|| 1
|--1---|--7---|------|--6---|------|--5---|------|| 4
+--.-------------.-------------.------------------+

Capo is also supported via the -c flag.

$./fretl -c3 -f7 -rC DAEABE < scales/major
   7      6      5      4      3      2      1      0
+---------.-------------.-------------.-----------+
|--D---|------|--C---|--B---|------|--A---|------|| G
|--A---|------|--G---|------|--F---|--E---|------|| D
|--G---|------|--F---|--E---|------|--D---|------|| C
|--D---|------|--C---|--B---|------|--A---|------|| G
|--G---|------|--F---|--E---|------|--D---|------|| C
|--C---|--B---|------|--A---|------|--G---|------|| F
+---------.-------------.-------------.-----------+

You could also pass in other scales as well.

$ fretl -f7 -rD CFCFAC < scales/minor
   7      6      5      4      3      2      1      0
+--.-------------.-------------.------------------+
|--G---|------|--F---|--E---|------|--D---|------|| C
|--E---|------|--D---|------|--C---|------|--Bb--|| A
|--C---|------|--Bb--|--A---|------|--G---|------|| F
|--G---|------|--F---|--E---|------|--D---|------|| C
|--C---|------|--Bb--|--A---|------|--G---|------|| F
|--G---|------|--F---|--E---|------|--D---|------|| C
+--.-------------.-------------.------------------+

Note that you don't need to specify which accidental to use. This is taken care of automatically.

Build

fretl is written in C99. Make sure you have a C99 compatible C compiler to build this program.

Since I separated the parsing and processing of music notes and intervals into separate libraries, you first need to update submodules by

$ git submodule update --init --recursive

Then use make to compile and install it to system:

$ make
# make install

You could also use the PREFIX option to install for current user only:

$ make PREFIX=~/.local install

Further reading

See

$ man 1 fretl

for the explanation of each option.