Florian WaltherandClaude Opus 5.5
e49fe6fe11
- $(command) is replaced by the output of command, which runs in a subshell (gosh -c), so cd/set in it do not change the shell - trailing newlines are removed; unquoted the output is split into words at blanks and newlines, "$(...)" stays one word; wildcards in the output are not expanded - nested substitutions, quotes and operators inside are handled; the list, alias and brace scanners skip $(...) as a whole - a command that consists only of a substitution has its exit status, Ctrl+C in a substitution aborts the command - $((...)) is reported as not supported Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
99 lines
2.4 KiB
Go
99 lines
2.4 KiB
Go
package main
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// Command substitution: $(command) is replaced by the output of command,
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// which runs in a subshell (a new gosh process), so that cd, set etc. in it
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// do not change the shell.
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import (
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"bytes"
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"errors"
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"os"
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"os/exec"
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"strings"
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"syscall"
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)
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// subshellPath is the gosh binary used for command substitution; empty means
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// the running executable. Tests set it, since there the running executable is
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// the test binary.
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var subshellPath string
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// substStatus is the exit status of the last command substitution of the
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// current command (a command that consists only of a substitution has this
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// status, like in sh).
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var substStatus int
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// isSubstStart reports whether a command substitution $( starts at s[i].
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func isSubstStart(s string, i int) bool {
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return s[i] == '$' && i+1 < len(s) && s[i+1] == '('
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}
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// substEnd returns the index of the ) that ends the command substitution
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// starting with $( at s[i], or -1 if it is not terminated. Quotes, escapes
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// and nested substitutions inside are taken into account.
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func substEnd(s string, i int) int {
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depth := 0
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var quote byte
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for j := i + 1; j < len(s); j++ {
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ch := s[j]
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switch {
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case quote == '\'':
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if ch == '\'' {
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quote = 0
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}
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case ch == '\\':
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j++
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case quote == '"':
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if ch == '"' {
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quote = 0
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} else if isSubstStart(s, j) {
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end := substEnd(s, j)
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if end < 0 {
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return -1
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}
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j = end
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}
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case ch == '"' || ch == '\'':
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quote = ch
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case ch == '(':
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depth++
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case ch == ')':
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depth--
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if depth == 0 {
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return j
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}
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}
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}
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return -1
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}
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// commandSubst runs command in a subshell and returns its output without
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// trailing newlines. stdin and stderr are those of the shell.
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func commandSubst(command string) (string, error) {
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if strings.HasPrefix(command, "(") {
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return "", errors.New("arithmetic expansion $((...)) is not supported")
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}
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path := subshellPath
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if path == "" {
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var err error
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if path, err = os.Executable(); err != nil {
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return "", err
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}
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}
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var out bytes.Buffer
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cmd := exec.Command(path, "-c", command)
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cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, &out, os.Stderr
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err := cmd.Run()
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substStatus = exitStatus(err)
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if substStatus == 128+int(syscall.SIGINT) {
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// Ctrl+C aborts the whole command, like in bash
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return "", statusError(substStatus)
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}
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var exitErr *exec.ExitError
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if err != nil && !errors.As(err, &exitErr) {
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return "", err
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}
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return strings.TrimRight(out.String(), "\n"), nil
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}
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