ls says in green what the shell will start

Directories were already blue. Something the shell will run is green now,
and it is asked by LOOKING rather than looked up.

This was priced once as needing a runnable bit in the directory entry,
set by the filesystem from a list of magic numbers it would have to be
taught - declined twice, for putting format knowledge in the filesystem
and giving two implementations a registry to keep in step.

It costs nothing of the sort any more. The shell decides what to run by
reading a file's first block, so "will this run" is a question with an
answer already, and this asks the same one the shell would: SBEX for a
program, "#!" for a script. Nothing is written down and nothing has to
agree about anything.

The price is a block read per file, which is exactly what the bit existed
to avoid: a listing of thirty seven files went from 260,593 cycles to
635,321. It is paid in ls and not in dir on purpose - dir is the listing
you audit and is built into the shell, this is the one you read and was
loaded off the disk anyway. The fast one stays fast.

plain.script is the proof on the test disk: it sits among a dozen scripts
that are green and is not one, because it is the fixture with no shebang
and the shell will not start it. The extension is decoration and the
colour is the truth, which is the whole of what running by content means,
finally visible.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E2JrLzFvuFX9fgi1LDRjrW

Programs/CosmOS/Apps/ls.asm

@@ -199,7 +199,8 @@ lsColour:
   ; ---- What it is, said in colour ----
   ;
   ; The attribute reaches a terminal as well as the screen now, so this is one mechanism and
-  ; not two. A directory in blue and an unfinished save in red; everything else plain.
+  ; not two. A directory in blue, something that will run in green, an unfinished save in red,
+  ; and everything else plain.
   SETD.0 Kind
   LDA.0
   BRA lsFileInk
@@ -212,6 +213,27 @@ lsBlue:
   BRI lsInk
 
 lsFileInk:
+  ; ---- Whether it will run, asked by looking ----
+  ;
+  ; This was priced once as needing a RUNNABLE BIT in the directory entry, set by the
+  ; filesystem from a list of magic numbers it would have to be taught - which was declined,
+  ; twice, for putting format knowledge in the filesystem and giving two implementations a
+  ; registry to keep in step.
+  ;
+  ; It costs nothing of the sort now. The shell decides what to run by READING the first block
+  ; of a file, so "will this run" is a question with an answer already, and asking it is the
+  ; same question the shell would ask. Nothing new is written down and nothing has to agree
+  ; about anything: if the shell learns a third kind of runnable file, this is wrong until
+  ; somebody adds two lines, and wrong in the direction of a listing that is less colourful.
+  ;
+  ; The price is a block read per file, which is what the bit existed to avoid. It is paid
+  ; here rather than in dir on purpose: dir is the listing you audit and is built into the
+  ; shell, and this is the one you read and is a program that was loaded off the disk anyway.
+  CALL runnable
+  BNQ lsPlain
+  INIA 0d2
+  BRI lsInk
+lsPlain:
   RSTA
 lsInk:
   OUTA 0x06
@@ -300,6 +322,67 @@ lengthDone:
   ADD
   RET
 
+; ---- Will the shell start this? ----
+;
+; Q is zero if it will. The same two things the shell itself looks for in a first block: SBEX
+; for a program, "#!" for a script. A file too short to have a first block at all cannot be
+; either, and osFileBlock saying no is that answer arriving for free.
+runnable:
+  SETD.0 Name
+  SETD.1 Block
+  RSTA
+  RSTB
+  SWI osFileBlock
+  BNQ runnableNo
+
+  ; The shebang first, because two bytes settle it.
+  SETD.0 Block
+  LDA.0
+  INIB 0d35                 ; '#'
+  CCF
+  SUB
+  BNQ runnableExec
+  INCD.0
+  LDA.0
+  INIB 0d33                 ; '!'
+  CCF
+  SUB
+  BRQ runnableYes
+
+runnableExec:
+  SETD.0 Block
+  SETD.1 ExecText
+  INIA 0d4
+  SETD.2 Left
+  STA.2
+runnableSame:
+  LDA.0
+  LDB.1
+  CCF
+  SUB
+  BNQ runnableNo
+  INCD.0
+  INCD.1
+  SETD.2 Left
+  LDA.2
+  DECA
+  STA.2
+  BNA runnableSame
+
+runnableYes:
+  RSTA
+  RSTB
+  CCF
+  ADD
+  RET
+
+runnableNo:
+  INIA 0x01
+  RSTB
+  CCF
+  ADD
+  RET
+
 ; A is how much of the cell the name took. Fills the rest of it with spaces.
 padOut:
   ; The cell less what the name took, and IN THAT ORDER. Written the other way round first,
@@ -337,6 +420,8 @@ newLine:
 
   #Base 0x3000
 
+ExecText:
+"SBEX"
 Slash:
 "/"
 Space:
@@ -362,7 +447,12 @@ Seen:
   0x00
 Used:
   0x00
+Left:
+  0x00
 Name:
   #Reserve 0d24
 Given:
   #Reserve 0d64
+; A whole block, because osFileBlock writes one whether the file fills it or not.
+Block:
+  #Reserve 0d256

Programs/CosmOS/README.md

@@ -724,6 +724,17 @@ sorting. Nothing here sorts; entries come back in the order the directory holds
 order arbitrary, down-and-across buys nothing and costs a division on a machine that cannot
 divide. If sorting ever arrives, that is the moment to change it.
 
+**Something that will run is green**, and that is asked by looking rather than looked up. The
+shell decides what to run by reading a file's first block, so "will this run" already has an
+answer and this asks the same question the shell would: `SBEX` for a program, `#!` for a
+script. It costs a block read per file, which is exactly the price a *runnable bit* in the
+directory entry was proposed to avoid - and that bit was declined twice for putting format
+knowledge in the filesystem and giving two implementations a registry to keep in step. Paying
+the price here instead buys the same listing and writes nothing down.
+
+It is paid in `ls` and not in `dir` on purpose. Reading every file roughly doubles what a
+listing costs; `dir` stays the fast one, and this one was loaded off the disk anyway.
+
 **The width comes from the screen**, port `0x32`, which is 80 while CosmOS is running because
 CosmOS asks for the wide mode as it starts.
 

Tests/expected/cosmosCrossDisk.out

@@ -49,7 +49,7 @@ pass.script             20
 holds.script            87
 crossed.txt             560
 36 files, 2 directories
-48 of 64 entries, 1887 blocks free
+48 of 64 entries, 1886 blocks free
 > exit
 halted
 Execution halted.

Tests/expected/cosmosDrives.out

@@ -40,7 +40,7 @@ args.script             64
 pass.script             20
 holds.script            87
 35 files, 2 directories
-47 of 64 entries, 1890 blocks free
+47 of 64 entries, 1889 blocks free
 > drive 1
 > dir
 other.txt               28

Tests/expected/cosmosFault.out

@@ -56,7 +56,7 @@ args.script             64
 pass.script             20
 holds.script            87
 35 files, 2 directories
-47 of 64 entries, 1890 blocks free
+47 of 64 entries, 1889 blocks free
 > exit
 halted
 Execution halted.

Tests/expected/cosmosFlip.out

@@ -44,7 +44,7 @@ args.script             64
 pass.script             20
 holds.script            87
 35 files, 2 directories
-47 of 64 entries, 1890 blocks free
+47 of 64 entries, 1889 blocks free
 > exit
 halted
 Execution halted.

Tests/expected/cosmosGrid.out

@@ -44,7 +44,7 @@ args.script             64
 pass.script             20
 holds.script            87
 35 files, 2 directories
-47 of 64 entries, 1890 blocks free
+47 of 64 entries, 1889 blocks free
 > exit
 halted
 Execution halted.

Tests/expected/cosmosLs.out

@@ -1,19 +1,19 @@
 CosmOS
 > ls
-greet.sbx      hello.sbx      Life.sbx       Snake.sbx      Keys.sbx
+greet.sbx      hello.sbx      Life.sbx       Snake.sbx      Keys.sbx
-Say.sbx        Where.sbx      Break.sbx      Grid.sbx       Press.sbx
+Say.sbx        Where.sbx      Break.sbx      Grid.sbx       Press.sbx
-Mode.sbx       Flip.sbx       Sprite.sbx     Depth.sbx      Packages/
+Mode.sbx       Flip.sbx       Sprite.sbx     Depth.sbx      Packages/
-Pad.sbx        Crash.sbx      vars.script    blocks.script  loops.script
+Pad.sbx        Crash.sbx      vars.script    blocks.script  loops.script
-tune.sbx       Play.sbx       notes.txt      Apps/          hi.script
+tune.sbx       Play.sbx       notes.txt      Apps/          hi.script
-bad.script     plain.script   cross.script   nonl.script    outer.script
+bad.script     plain.script   cross.script   nonl.script    outer.script
-inner.script   loop.script    hush.script    aloud.script   args.script
+inner.script   loop.script    hush.script    aloud.script   args.script
-pass.script    holds.script
+pass.script    holds.script
 > cd /Apps
 /Apps> ls
-Copy.sbx   Say.sbx    Where.sbx  Walk.sbx   ls.sbx     Lander     where.sh
+Copy.sbx   Say.sbx    Where.sbx  Walk.sbx   ls.sbx     Lander     where.sh
 /Apps> cd /
 > ls /Packages/app.Lander
-Lander.sbx   splash.tune
+Lander.sbx   splash.tune
 > mkdir /empty
 made
 > cd /empty

Tests/expected/cosmosMonitor.out

@@ -132,7 +132,7 @@ args.script             64
 pass.script             20
 holds.script            87
 35 files, 2 directories
-47 of 64 entries, 1890 blocks free
+47 of 64 entries, 1889 blocks free
 > exit
 halted
 Execution halted.

Tests/expected/cosmosMonitorRun.out

@@ -51,7 +51,7 @@ args.script             64
 pass.script             20
 holds.script            87
 35 files, 2 directories
-47 of 64 entries, 1890 blocks free
+47 of 64 entries, 1889 blocks free
 > exit
 halted
 Execution halted.

Tests/expected/cosmosRun.out

@@ -40,7 +40,7 @@ args.script             64
 pass.script             20
 holds.script            87
 35 files, 2 directories
-47 of 64 entries, 1890 blocks free
+47 of 64 entries, 1889 blocks free
 > load
 load what?
 > load nosuch.sbx

Tests/expected/cosmosSlowDisk.out

@@ -38,7 +38,7 @@ args.script             64
 pass.script             20
 holds.script            87
 35 files, 2 directories
-47 of 64 entries, 1890 blocks free
+47 of 64 entries, 1889 blocks free
 > load Say.sbx
 loaded, starting at 5000
 > run the disk took its time

Tests/expected/cosmosSpace.out

@@ -38,7 +38,7 @@ args.script             64
 pass.script             20
 holds.script            87
 35 files, 2 directories
-47 of 64 entries, 1890 blocks free
+47 of 64 entries, 1889 blocks free
 > drive 1
 > dir
 f1.txt                  1500

Tests/expected/cosmosSprite.out

@@ -44,7 +44,7 @@ args.script             64
 pass.script             20
 holds.script            87
 35 files, 2 directories
-47 of 64 entries, 1890 blocks free
+47 of 64 entries, 1889 blocks free
 > exit
 halted
 Execution halted.

Tests/expected/cosmosWalk.out

@@ -43,7 +43,7 @@ f Copy.sbx 7
 f Say.sbx 1
 f Where.sbx 4
 f Walk.sbx 1
-f ls.sbx 3
+f ls.sbx 4
 f Lander 4
 f where.sh 3
 /Apps> cd /