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jdx merged 3 commits into from
Jan 31, 2026
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docs: add bash array pattern for variadic args #480

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docs: add bash array pattern for variadic args
jdx Jan 30, 2026
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docs: add note about readarray/mapfile bash version requirements
jdx Jan 30, 2026
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docs: remove incorrect note about readarray/mapfile
jdx Jan 30, 2026
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25 changes: 25 additions & 0 deletions docs/spec/reference/arg.md
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Original file line number Diff line number Diff line change
Expand Up @@ -13,7 +13,32 @@ arg "<file>" var=#true # multiple args can be passed (e.g. mycli file1 file2 fil
arg "<file>..." # shorthand for var=#true (trailing ellipsis)
arg "<file>" var=#true var_min=3 # at least 3 args must be passed
arg "<file>" var=#true var_max=3 # up to 3 args can be passed
```

## Using Variadic Args in Bash

When using variadic arguments (`var=#true`), the values are passed as a shell-escaped
string via the `usage_<name>` environment variable. To properly handle arguments
containing spaces as a bash array, wrap the variable in parentheses:

```bash
# Given: usage_files="arg1 'arg with space' arg3"

# Convert to bash array:
eval "files=($usage_files)"

Copilot AI Jan 30, 2026

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Using eval with user-controlled input can introduce command injection vulnerabilities. If usage_files contains malicious shell commands, they will be executed. Consider documenting safer alternatives such as using readarray with process substitution, or add prominent security warnings about input validation if eval is necessary.

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@gemini-code-assist gemini-code-assist Bot Jan 30, 2026

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security-high high

The use of eval here is vulnerable to globbing. If a user provides an argument like *, it will be expanded to a list of all files in the current directory, which can lead to unexpected behavior and security risks. To make this example safer for users to copy and paste, it's crucial to disable globbing before the eval command and restore it afterward.

Suggested change
eval "files=($usage_files)"
set -f # Disable globbing to prevent filename expansion
eval "files=($usage_files)"
set +f # Re-enable globbing
References
  1. When using eval to parse a string into shell arguments, it's important to disable globbing (set -f) to prevent unintended filename expansion from characters like * and ? in the input string. This is a common security best practice for writing robust shell scripts.


# Now use as array:
for f in "${files[@]}"; do
echo "Processing: $f"
done

# Or pass to commands:
touch "${files[@]}"
```

This pattern ensures arguments with spaces are handled correctly as separate elements.

```kdl
arg "<shell>" {
choices "bash" "zsh" "fish" # <shell> must be one of the choices
}
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