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// Copyright 2015 Canonical Ltd.
// Licensed under the LGPLv3, see LICENCE file for details.
package shell
import (
"strconv"
"strings"
)
// OutputRenderer exposes the Renderer methods that relate to shell output.
//
// The methods all accept strings to identify their file descriptor
// arguments. While the interpretation of these values is up to the
// renderer, it will likely conform to the result of calling ResolveFD.
// If an FD arg is not recognized then no commands will be returned.
// Unless otherwise specified, the default file descriptor is stdout
// (FD 1). This applies to the empty string.
type OutputRenderer interface {
// RedirectFD returns a shell command that redirects the src
// file descriptor to the dst one.
RedirectFD(dst, src string) []string
// TODO(ericsnow) Add CopyFD and CreateFD?
// TODO(ericsnow) Support passing the src FD as an arg?
// RedirectOutput will cause all subsequent output from the shell
// (or script) to go be appended to the given file. Only stdout is
// redirected (use RedirectFD to redirect stderr or other FDs).
//
// The file should already exist (so a call to Touch may be
// necessary before calling RedirectOutput). If the file should have
// specific permissions or a specific owner then Chmod and Chown
// should be called before calling RedirectOutput.
RedirectOutput(filename string) []string
// RedirectOutputReset will cause all subsequent output from the
// shell (or script) to go be written to the given file. The file
// will be reset (truncated to 0) before anything is written. Only
// stdout is redirected (use RedirectFD to redirect stderr or
// other FDs).
//
// The file should already exist (so a call to Touch may be
// necessary before calling RedirectOutputReset). If the file should
// have specific permissions or a specific owner then Chmod and
// Chown should be called before calling RedirectOutputReset.
RedirectOutputReset(filename string) []string
}
// ResolveFD converts the file descriptor name to the corresponding int.
// "stdout" and "out" match stdout (FD 1). "stderr" and "err" match
// stderr (FD 2), "stdin" and "in" match stdin (FD 0). All positive
// integers match. If there should be an upper bound then the caller
// should check it on the result. If the provided name is empty then
// the result defaults to stdout. If the name is not recognized then
// false is returned.
func ResolveFD(name string) (int, bool) {
switch strings.ToLower(name) {
case "stdout", "out", "":
return 1, true
case "stderr", "err":
return 2, true
case "stdin", "in":
return 0, true
default:
fd, err := strconv.ParseUint(name, 10, 64)
if err != nil {
return -1, false
}
return int(fd), true
}
}
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