feat(builtins): implement printf %q shell quoting

crates/bashkit/src/builtins/printf.rs

@@ -343,6 +343,10 @@ fn format_string(format: &str, args: &[String], arg_index: &mut usize) -> String
                             // String with escape sequences
                             output.push_str(&expand_escapes(arg));
                         }
+                        'q' => {
+                            // Shell-quoted string safe for reuse
+                            output.push_str(&shell_quote(arg));
+                        }
                         _ => {
                             // Unknown format - output literally
                             output.push('%');
@@ -363,6 +367,63 @@ fn format_string(format: &str, args: &[String], arg_index: &mut usize) -> String
     output
 }
 
+/// Quote a string for safe shell reuse (printf %q behavior).
+///
+/// Matches bash behavior:
+/// - Empty string → `''`
+/// - Safe strings (only alnum/`_`/`.`/`-`/`:`/`=`/`+`/`@`/`,`/`%`/`^`/`/`) → unquoted
+/// - Strings with control chars (tab, newline, etc.) → `$'...'` quoting
+/// - Other strings → backslash-escape individual special characters
+fn shell_quote(s: &str) -> String {
+    if s.is_empty() {
+        return "''".to_string();
+    }
+
+    // Check if the string needs quoting at all
+    let needs_quoting = s
+        .chars()
+        .any(|c| !c.is_ascii_alphanumeric() && !"_/.:-=+@,%^".contains(c));
+
+    if !needs_quoting {
+        return s.to_string();
+    }
+
+    // Check for control characters that require $'...' quoting
+    let has_control = s.chars().any(|c| (c as u32) < 32 || c as u32 == 127);
+
+    if has_control {
+        // Use $'...' quoting
+        let mut out = String::from("$'");
+        for ch in s.chars() {
+            match ch {
+                '\'' => out.push_str("\\'"),
+                '\\' => out.push_str("\\\\"),
+                '\n' => out.push_str("\\n"),
+                '\t' => out.push_str("\\t"),
+                '\r' => out.push_str("\\r"),
+                c if (c as u32) < 32 || c as u32 == 127 => {
+                    out.push_str(&format!("\\x{:02x}", c as u32));
+                }
+                c => out.push(c),
+            }
+        }
+        out.push('\'');
+        out
+    } else {
+        // Backslash-escape individual special characters
+        let mut out = String::new();
+        for ch in s.chars() {
+            if ch.is_ascii_alphanumeric() || "_/.:-=+@,%^".contains(ch) {
+                out.push(ch);
+            } else {
+                out.push('\\');
+                out.push(ch);
+            }
+        }
+        out
+    }
+}
+
 /// Expand escape sequences in a string
 fn expand_escapes(s: &str) -> String {
     let mut output = String::new();

crates/bashkit/tests/spec_cases/bash/printf.test.sh

@@ -197,3 +197,47 @@ printf -v padded "%05d" 42; echo "$padded"
 ### expect
 00042
 ### end
+
+### printf_q_space
+# printf %q escapes spaces
+printf '%q\n' 'hello world'
+### expect
+hello\ world
+### end
+
+### printf_q_simple
+# printf %q leaves safe strings unquoted
+printf '%q\n' 'simple'
+### expect
+simple
+### end
+
+### printf_q_empty
+# printf %q quotes empty string
+printf '%q\n' ''
+### expect
+''
+### end
+
+### printf_q_special_chars
+# printf %q escapes special shell chars
+printf '%q\n' 'a"b'
+### expect
+a\"b
+### end
+
+### printf_q_tab
+# printf %q uses $'...' for control chars
+### bash_diff
+x=$(printf 'hello\tworld')
+printf '%q\n' "$x"
+### expect
+$'hello\tworld'
+### end
+
+### printf_q_single_quote
+# printf %q escapes single quotes
+printf '%q\n' "it's"
+### expect
+it\'s
+### end

specs/009-implementation-status.md

@@ -103,17 +103,17 @@ Bashkit implements IEEE 1003.1-2024 Shell Command Language. See
 
 ## Spec Test Coverage
 
-**Total spec test cases:** 1359 (1354 pass, 5 skip)
+**Total spec test cases:** 1365 (1360 pass, 5 skip)
 
 | Category | Cases | In CI | Pass | Skip | Notes |
 |----------|-------|-------|------|------|-------|
-| Bash (core) | 941 | Yes | 936 | 5 | `bash_spec_tests` in CI |
+| Bash (core) | 947 | Yes | 942 | 5 | `bash_spec_tests` in CI |
 | AWK | 96 | Yes | 96 | 0 | loops, arrays, -v, ternary, field assign, getline, %.6g |
 | Grep | 76 | Yes | 76 | 0 | -z, -r, -a, -b, -H, -h, -f, -P, --include, --exclude, binary detect |
 | Sed | 75 | Yes | 75 | 0 | hold space, change, regex ranges, -E |
 | JQ | 114 | Yes | 114 | 0 | reduce, walk, regex funcs, --arg/--argjson, combined flags, input/inputs, env |
 | Python | 57 | Yes | 57 | 0 | embedded Python (Monty) |
-| **Total** | **1359** | **Yes** | **1354** | **5** | |
+| **Total** | **1365** | **Yes** | **1360** | **5** | |
 
 ### Bash Spec Tests Breakdown
 
@@ -149,7 +149,7 @@ Bashkit implements IEEE 1003.1-2024 Shell Command Language. See
 | paste.test.sh | 4 | line merging with `-s` serial and `-d` delimiter |
 | path.test.sh | 14 | |
 | pipes-redirects.test.sh | 19 | includes stderr redirects |
-| printf.test.sh | 26 | format specifiers, array expansion, `-v` variable assignment |
+| printf.test.sh | 32 | format specifiers, array expansion, `-v` variable assignment, `%q` shell quoting |
 | procsub.test.sh | 6 | |
 | sleep.test.sh | 6 | |
 | sortuniq.test.sh | 32 | sort and uniq, `-z` zero-terminated, `-m` merge |