Befunge-98 (FBBI), 344 296 248 bytes

20020xxnngg33%%!!2200gg''00--3300gg33%%!!4400gg55%%!!22kk++55##rr55kk::00gg\\11pp00gg\\11++11pp22++00::pp00gg\\11++00gg--!!zz!!22**++00::gg00gg8844**--!!55++jj..''gg::00rr00::gg\\--..''220011''0011::''002211''223311''00441144kkppgg11001100::99oo@@

Try it online!

Verification!

Befunge-98 is the first esoteric language that I could find that was both 2D and had file output. This is a full solution (with a trailing newline) stored in a file named as a tab character. There's a few golfs to be made, especially as there are 15 no-ops in the code, now just one no-op! I will be working on making this shorter, with the goal of getting to or below 200 bytes.

Befunge-98 (FBBI), 344 296 248 bytes

20020xxnngg33%%!!2200gg''00--3300gg33%%!!4400gg55%%!!22kk++55##rr55kk::00gg\\11pp00gg\\11++11pp22++00::pp00gg\\11++00gg--!!zz!!22**++00::gg00gg8844**--!!55++jj..''gg::00rr00::gg\\--..''220011''0011::''002211''223311''00441144kkppgg11001100::99oo@@

Try it online!

Verification!

Befunge-98 is the first esoteric language that I could find that was both 2D and had file output. This is a full solution (with a trailing newline) stored in a file named as a tab character. It outputs as 0-indexed, and outputs the first index in a run of characters (though there's only ever pairs).

There's a few golfs to be made, especially as there are 15 no-ops in the code, now just one no-op! I will be working on making this shorter, with the goal of getting to or below 200 bytes.

Befunge-98 (FBBI), 344 296 bytes

20020xxnngg2200gg3300gg4400gg''xx--!!\\''00--!!++\\''22--!!22**++\\''00--!!++5500::pp##rr00::gg33kk::00gg::00::gg11pp\\11++11pp22++00::pp00gg\\11++00gg--!!zz!!22**++00::gg00gg8844**--!!33++jj**aa55rrddbb**22**99++\\--..''220011''0011::''002211''223311''00441144kkppddbb**22**99++11001100::99oo@@

Try it online!

Verification!

Befunge-98 is the first esoteric language that I could find that was both 2D and had file output. This is a full solution (with a trailing newline) stored in a file named as a tab character. There's a few golfs to be made, especially as there are 15 no-ops in the code, now just one no-op! I will be working on making this shorter.

Befunge-98 (FBBI), 344 296 248 bytes

20020xxnngg33%%!!2200gg''00--3300gg33%%!!4400gg55%%!!22kk++55##rr55kk::00gg\\11pp00gg\\11++11pp22++00::pp00gg\\11++00gg--!!zz!!22**++00::gg00gg8844**--!!55++jj..''gg::00rr00::gg\\--..''220011''0011::''002211''223311''00441144kkppgg11001100::99oo@@

Try it online!

Verification!

Befunge-98 is the first esoteric language that I could find that was both 2D and had file output. This is a full solution (with a trailing newline) stored in a file named as a tab character. There's a few golfs to be made, especially as there are 15 no-ops in the code, now just one no-op! I will be working on making this shorter, with the goal of getting to or below 200 bytes.

Befunge-98 (FBBI), 344 bytes

20020xx00zz00gg2200gg3300gg4400gg''xx--!!\\''00--!!++\\''22--!!22**++\\''00--!!++5500zz00pp##rrzz00zz00zzggzz::zz::zz::zz::00gg::00zz00gg11pp\\11++11pp22++00zz00pp00gg\\11++00gg--!!zz!!22**++00zz00gg00gg8844**--!!33++jj**aa66rreecc**22**77++\\--..''220011''0011zz11''002211''223311''00441144kkppeecc**22**77++11001100zz00""8899bb..ttuuoo""oo@@

Try it online!

Verification!

Befunge-98 is the first esoteric language that I could find that was both 2D and had file output. This is a full solution (with a trailing newline) stored in a file called out.b98. There's a few golfs to be made, especially as there are 15 no-ops in the code to separate identical pairs of characters, and I will be working on making this shorter. I suspect this can be easily under 300 bytes.

Befunge-98 (FBBI), 344 296 bytes

20020xxnngg2200gg3300gg4400gg''xx--!!\\''00--!!++\\''22--!!22**++\\''00--!!++5500::pp##rr00::gg33kk::00gg::00::gg11pp\\11++11pp22++00::pp00gg\\11++00gg--!!zz!!22**++00::gg00gg8844**--!!33++jj**aa55rrddbb**22**99++\\--..''220011''0011::''002211''223311''00441144kkppddbb**22**99++11001100::99oo@@

Try it online!

Verification!

Befunge-98 is the first esoteric language that I could find that was both 2D and had file output. This is a full solution (with a trailing newline) stored in a file named as a tab character. There's a few golfs to be made, especially as there are 15 no-ops in the code, now just one no-op! I will be working on making this shorter.