Deno: NotCapable: Requires read access to "data.txt", run again with the --allow-read flag

NotCapable: Requires read access to "data.txt", run again with the --allow-read flag means the script tried to read a file and Deno's permission system blocked it. Deno runs code without file, network, environment or subprocess access unless you grant it. Add --allow-read to the deno run command, preferably scoped to the path the script needs: deno run --allow-read=data.txt main.ts.

Reproduce it

echo "hello" > data.txt
echo 'console.log(Deno.readTextFileSync("data.txt"));' > main.ts
npx --yes deno@2 run main.ts 2>&1 | head -1
exit "${PIPESTATUS[0]}"

error: Uncaught (in promise) NotCapable: Requires read access to "data.txt", run again with the --allow-read flag

Only the first line is kept; Deno also prints the source line and a stack trace. Without a terminal (CI, scripts, this run) Deno does not prompt and the call fails at once. In an interactive terminal Deno first asks Allow? and the error appears only if you answer no.

Fix

echo "hello" > data.txt
echo 'console.log(Deno.readTextFileSync("data.txt"));' > main.ts
npx --yes deno@2 run --allow-read=data.txt main.ts

hello

The same message exists for every permission, with the matching flag in the text:

In Deno 1.x the same failure was reported as PermissionDenied; Deno 2 uses the NotCapable error class, so code that checks instanceof Deno.errors.PermissionDenied must be updated.