Documentation

Execute a system command. Before running command make sure you need any files that are required by the command.

This function takes a list of options (often just [], see CmdOption for the available options), the name of the executable (either a full name, or a program on the $PATH) and a list of arguments. The result is often (), but can be a tuple containg any of Stdout, Stderr and Exit. Some examples:

 command_ [] "gcc" ["-c","myfile.c"]                          -- compile a file, throwing an exception on failure
 Exit c <- command [] "gcc" ["-c",myfile]                     -- run a command, recording the exit code
 (Exit c, Stderr err) <- command [] "gcc" ["-c","myfile.c"]   -- run a command, recording the exit code and error output
 Stdout out <- command [] "gcc" ["-MM","myfile.c"]            -- run a command, recording the output
 command_ [Cwd "generated"] "gcc" ["-c",myfile]               -- run a command in a directory

Unless you retrieve the ExitCode using Exit, any ExitFailure will throw an error, including the Stderr in the exception message. If you capture the Stdout or Stderr, that stream will not be echoed to the console, unless you use the option EchoStdout or EchoStderr.

If you use command inside a do block and do not use the result, you may get a compile-time error about being unable to deduce CmdResult. To avoid this error, use command_.

A version of command where you do not require any results, used to avoid errors about being unable to deduce CmdResult.

A variable arity version of command.

• String arguments are treated as whitespace separated arguments.
• [String] arguments are treated as literal arguments.
• CmdOption arguments are used as options.

To take the examples from command:

 () <- cmd "gcc -c myfile.c"                                  -- compile a file, throwing an exception on failure
 Exit c <- cmd "gcc -c" [myfile]                              -- run a command, recording the exit code
 (Exit c, Stderr err) <- cmd "gcc -c myfile.c"                -- run a command, recording the exit code and error output
 Stdout out <- cmd "gcc -MM myfile.c"                         -- run a command, recording the output
 cmd (Cwd "generated") "gcc -c" [myfile] :: Action ()         -- run a command in a directory

When passing file arguments we use [myfile] so that if the myfile variable contains spaces they are properly escaped.

If you use cmd inside a do block and do not use the result, you may get a compile-time error about being unable to deduce CmdResult. To avoid this error, bind the result to (), or include a type signature.

Collect the stdout of the process. If you are collecting the stdout, it will not be echoed to the terminal, unless you include EchoStdout.

Collect the stderr of the process. If you are collecting the stderr, it will not be echoed to the terminal, unless you include EchoStderr.

Collect the ExitCode of the process. If you do not collect the exit code, any ExitFailure will cause an exception.

A class for specifying what results you want to collect from a process. Values are formed of Stdout, Stderr, Exit and tuples of those.

Options passed to command or cmd to control how processes are executed.