EN Course 08 Bash Tool Permission Mode

Bash Tool Permission Mode

Bash is the most powerful tool, so it is classified before execution.

The policy uses four scopes:

system external network workspace

Each digit uses rwx bits:

4 = read
2 = write
1 = execute

Default:

0 4 4 7
| | | |
| | | `- workspace = read + write + execute
| | `--- network   = read
| `----- external  = read
`------- system    = none

Scanner Shape

The scanner converts a command into required=....:

tool_classify_bash_required_mode() {
    local cmd="$1" lowered
    TOOL_BASH_REQUIRED_MASK=0
    lowered=$(printf '%s' "$cmd" | tr '[:upper:]' '[:lower:]')
    tool_bash_scan_script "$lowered"
    (( TOOL_BASH_REQUIRED_MASK == 0 )) && tool_bash_add_mode 1 4
    printf -v TOOL_BASH_REQUIRED_MODE '%04o' "$TOOL_BASH_REQUIRED_MASK"
}

Then tool_bash_mode_allows checks whether the allowed mask covers the required mask.

Classification Examples

Typical command outcomes under the default mode (0447):

Command	Required scope/bit (simplified)	Default decision
cat README.md	workspace read	allow
echo hi > out.txt	workspace write	allow
chmod +x script.sh	workspace execute/write	allow
curl https://example.com	network read	allow
git status	workspace read	allow
ssh host	network execute pattern	deny
rm -rf /tmp/x	workspace write	allow
rm -rf /etc/hosts	system write	deny
sudo apt install ...	system write/execute	deny
launchctl unload ...	system control	deny

The exact classifier is conservative and implementation-specific; the table is for mental model and review.

Design Boundary

This is not a full Bash parser. It is a conservative scanner that recognizes common paths, redirects, network commands, execution patterns, and dangerous system operations.

The important invariant is parity: Bash, C, Go, and Rust should classify the same command the same way and return the same block message.

For deeper details, see Bash Tool Permission Mode.

Next

Plan and Todo Workflow explains how planning and progress tracking are modeled before introducing child agent runtimes.