Scripting¶

A script is just a file of shell commands, one per line, run with run. The shell also has a tiny expression language: 26 integer variables, arithmetic, a conditional, and a counted loop.

Variables and expressions¶

There are 26 integer (16-bit) variables, a through z. Assign one with set; an expression may mix literals and other variables:

$ set x 5
$ set y $x + 3 * 2
$ say $y
16

$x anywhere on a line expands to the decimal value of variable x before the command runs. Expressions use + - * / evaluated left to right, with no precedence: $x + 3 * 2 is (5 + 3) * 2 = 16.

Expansion timing and the `\$` escape¶

$x expands when the line runs. For a command redirected into a file, that is at write time, so the variable’s current value is baked into the file:

$ set n 9
$ say got $n >> f     # writes "got 9" -- the value, not the reference
$ cat f
got 9

To save a literal $x into a file — so a script re-evaluates it each time it runs — escape the dollar with a backslash, \$:

$ set m 5
$ say say got \$m >> g    # writes the literal "say got $m"
$ run g
got 5
$ set m 9
$ run g                   # re-renders: now prints "got 9"

Conditionals¶

if <a> <op> <b> <command> runs <command> when the comparison holds. The operators are two-letter mnemonics — eq ne lt le gt ge — chosen so they never collide with the > / < redirection operators:

$ if 5 gt 3 say yes
yes
$ if 2 gt 9 say no

Loops¶

rep <n> <command> runs <command> n times:

$ rep 3 say hi
hi
hi
hi

Building and running a script¶

Write the script with redirection, then run it:

$ say sbi 0x37 5 >> flash      # PB5 = output
$ say sbi 0x38 5 >> flash      # PB5 high
$ say slp 20 >> flash          # wait ~0.25 s
$ say cbi 0x38 5 >> flash      # PB5 low
$ run flash

A script’s effects persist: a set inside the script updates the same variables the interactive shell sees.

Limits¶

Lines are at most 62 characters.
Scripts run one level deep: a run or a nested rep inside a running script is not re-entered.