| 1 | //! Internal command substitution execution |
| 2 | //! |
| 3 | //! This module provides the ability to execute commands internally and capture their stdout, |
| 4 | //! enabling $(command) substitution without relying on external shells. |
| 5 | |
| 6 | use rush_expand::Context; |
| 7 | |
| 8 | /// Execute a command string internally and capture its stdout |
| 9 | /// |
| 10 | /// This is the callback function that gets registered with Context.command_executor |
| 11 | /// to enable internal command substitution. |
| 12 | /// |
| 13 | /// The function: |
| 14 | /// 1. Parses the command string using rush-parser |
| 15 | /// 2. Forks a child process |
| 16 | /// 3. The child executes the command with stdout redirected to a pipe |
| 17 | /// 4. The parent reads and returns the captured output |
| 18 | pub fn execute_for_substitution(cmd: &str, context: &mut Context) -> Result<String, String> { |
| 19 | // Parse the command |
| 20 | let statement = rush_parser::parse_line(cmd) |
| 21 | .map_err(|e| format!("Parse error: {}", e))?; |
| 22 | |
| 23 | // Use fork + pipe to capture stdout (like bash does) |
| 24 | #[cfg(unix)] |
| 25 | { |
| 26 | execute_with_fork_capture(statement, context) |
| 27 | } |
| 28 | |
| 29 | #[cfg(not(unix))] |
| 30 | { |
| 31 | // On non-Unix platforms, fall back to sh -c for now |
| 32 | // TODO: Implement Windows-specific stdout capture |
| 33 | Err("Command substitution on non-Unix platforms not yet supported".to_string()) |
| 34 | } |
| 35 | } |
| 36 | |
| 37 | #[cfg(unix)] |
| 38 | fn execute_with_fork_capture( |
| 39 | statement: rush_parser::Statement, |
| 40 | context: &mut Context, |
| 41 | ) -> Result<String, String> { |
| 42 | use nix::libc; |
| 43 | use nix::unistd::{pipe, dup2, fork, ForkResult}; |
| 44 | use nix::sys::wait::{waitpid, WaitStatus}; |
| 45 | use std::os::unix::io::{RawFd, FromRawFd, IntoRawFd}; |
| 46 | use std::io::{Read, Write}; |
| 47 | |
| 48 | const STDOUT_FD: RawFd = 1; |
| 49 | |
| 50 | // Create a pipe for capturing output |
| 51 | let (read_fd, write_fd) = pipe().map_err(|e| format!("Failed to create pipe: {}", e))?; |
| 52 | let read_raw_fd = read_fd.into_raw_fd(); |
| 53 | let write_raw_fd = write_fd.into_raw_fd(); |
| 54 | |
| 55 | // Fork to execute the command in a subprocess |
| 56 | match unsafe { fork() } { |
| 57 | Ok(ForkResult::Child) => { |
| 58 | // Child process: redirect stdout to pipe and execute |
| 59 | |
| 60 | // Close the read end of the pipe (child only writes) |
| 61 | unsafe { libc::close(read_raw_fd); } |
| 62 | |
| 63 | // Redirect stdout to the write end of the pipe |
| 64 | if let Err(_) = dup2(write_raw_fd, STDOUT_FD) { |
| 65 | std::process::exit(1); |
| 66 | } |
| 67 | |
| 68 | // Close the original write_fd (now that stdout points to it) |
| 69 | unsafe { libc::close(write_raw_fd); } |
| 70 | |
| 71 | // Execute the command |
| 72 | let exit_code = match statement { |
| 73 | rush_parser::Statement::Complete(cmd) => { |
| 74 | match crate::control_flow::execute_complete_command(&cmd, context) { |
| 75 | Ok(result) => result.exit_code(), |
| 76 | Err(_) => 1, |
| 77 | } |
| 78 | } |
| 79 | rush_parser::Statement::Script(commands) => { |
| 80 | let mut last_code = 0; |
| 81 | for cmd in &commands { |
| 82 | match crate::control_flow::execute_complete_command(cmd, context) { |
| 83 | Ok(result) => last_code = result.exit_code(), |
| 84 | Err(_) => { |
| 85 | last_code = 1; |
| 86 | break; |
| 87 | } |
| 88 | } |
| 89 | } |
| 90 | last_code |
| 91 | } |
| 92 | rush_parser::Statement::Empty => 0, |
| 93 | }; |
| 94 | |
| 95 | // Ensure all output is flushed before exiting |
| 96 | let _ = std::io::stdout().flush(); |
| 97 | |
| 98 | // Exit the child process |
| 99 | std::process::exit(exit_code); |
| 100 | } |
| 101 | Ok(ForkResult::Parent { child }) => { |
| 102 | // Parent process: close write end and read from pipe |
| 103 | |
| 104 | // Close the write end (parent only reads) |
| 105 | unsafe { libc::close(write_raw_fd); } |
| 106 | |
| 107 | // Read all output from the pipe |
| 108 | let mut output = String::new(); |
| 109 | let mut reader = unsafe { std::fs::File::from_raw_fd(read_raw_fd) }; |
| 110 | if let Err(e) = reader.read_to_string(&mut output) { |
| 111 | return Err(format!("Failed to read output: {}", e)); |
| 112 | } |
| 113 | |
| 114 | // Wait for child to complete |
| 115 | match waitpid(child, None) { |
| 116 | Ok(WaitStatus::Exited(_, code)) => { |
| 117 | context.set_exit_status(code); |
| 118 | } |
| 119 | Ok(_) => { |
| 120 | context.set_exit_status(0); |
| 121 | } |
| 122 | Err(e) => { |
| 123 | return Err(format!("Failed to wait for child: {}", e)); |
| 124 | } |
| 125 | } |
| 126 | |
| 127 | // Bash behavior: trim trailing newlines from command substitution |
| 128 | while output.ends_with('\n') { |
| 129 | output.pop(); |
| 130 | } |
| 131 | |
| 132 | Ok(output) |
| 133 | } |
| 134 | Err(e) => { |
| 135 | // Fork failed, clean up |
| 136 | unsafe { |
| 137 | libc::close(read_raw_fd); |
| 138 | libc::close(write_raw_fd); |
| 139 | } |
| 140 | Err(format!("Failed to fork: {}", e)) |
| 141 | } |
| 142 | } |
| 143 | } |
| 144 | |
| 145 | #[cfg(test)] |
| 146 | mod tests { |
| 147 | use super::*; |
| 148 | |
| 149 | #[test] |
| 150 | #[cfg(unix)] |
| 151 | fn test_internal_echo() { |
| 152 | let mut context = Context::empty(); |
| 153 | let result = execute_for_substitution("echo hello", &mut context).unwrap(); |
| 154 | assert_eq!(result, "hello"); |
| 155 | } |
| 156 | |
| 157 | #[test] |
| 158 | #[cfg(unix)] |
| 159 | fn test_internal_with_variables() { |
| 160 | let mut context = Context::empty(); |
| 161 | context.set_var("x", "world").unwrap(); |
| 162 | let result = execute_for_substitution("echo hello $x", &mut context).unwrap(); |
| 163 | assert_eq!(result, "hello world"); |
| 164 | } |
| 165 | } |
| 166 |