Preview: env.go
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/proc/thread-self/root/opt/golang/1.22.0/src/os/env.go
// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// General environment variables.
package os
import (
"internal/testlog"
"syscall"
)
// Expand replaces ${var} or $var in the string based on the mapping function.
// For example, os.ExpandEnv(s) is equivalent to os.Expand(s, os.Getenv).
func Expand(s string, mapping func(string) string) string {
var buf []byte
// ${} is all ASCII, so bytes are fine for this operation.
i := 0
for j := 0; j < len(s); j++ {
if s[j] == '$' && j+1 < len(s) {
if buf == nil {
buf = make([]byte, 0, 2*len(s))
}
buf = append(buf, s[i:j]...)
name, w := getShellName(s[j+1:])
if name == "" && w > 0 {
// Encountered invalid syntax; eat the
// characters.
} else if name == "" {
// Valid syntax, but $ was not followed by a
// name. Leave the dollar character untouched.
buf = append(buf, s[j])
} else {
buf = append(buf, mapping(name)...)
}
j += w
i = j + 1
}
}
if buf == nil {
return s
}
return string(buf) + s[i:]
}
// ExpandEnv replaces ${var} or $var in the string according to the values
// of the current environment variables. References to undefined
// variables are replaced by the empty string.
func ExpandEnv(s string) string {
return Expand(s, Getenv)
}
// isShellSpecialVar reports whether the character identifies a special
// shell variable such as $*.
func isShellSpecialVar(c uint8) bool {
switch c {
case '*', '#', '$', '@', '!', '?', '-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
return true
}
return false
}
// isAlphaNum reports whether the byte is an ASCII letter, number, or underscore.
func isAlphaNum(c uint8) bool {
return c == '_' || '0' <= c && c <= '9' || 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z'
}
// getShellName returns the name that begins the string and the number of bytes
// consumed to extract it. If the name is enclosed in {}, it's part of a ${}
// expansion and two more bytes are needed than the length of the name.
func getShellName(s string) (string, int) {
switch {
case s[0] == '{':
if len(s) > 2 && isShellSpecialVar(s[1]) && s[2] == '}' {
return s[1:2], 3
}
// Scan to closing brace
for i := 1; i < len(s); i++ {
if s[i] == '}' {
if i == 1 {
return "", 2 // Bad syntax; eat "${}"
}
return s[1:i], i + 1
}
}
return "", 1 // Bad syntax; eat "${"
case isShellSpecialVar(s[0]):
return s[0:1], 1
}
// Scan alphanumerics.
var i int
for i = 0; i < len(s) && isAlphaNum(s[i]); i++ {
}
return s[:i], i
}
// Getenv retrieves the value of the environment variable named by the key.
// It returns the value, which will be empty if the variable is not present.
// To distinguish between an empty value and an unset value, use LookupEnv.
func Getenv(key string) string {
testlog.Getenv(key)
v, _ := syscall.Getenv(key)
return v
}
// LookupEnv retrieves the value of the environment variable named
// by the key. If the variable is present in the environment the
// value (which may be empty) is returned and the boolean is true.
// Otherwise the returned value will be empty and the boolean will
// be false.
func LookupEnv(key string) (string, bool) {
testlog.Getenv(key)
return syscall.Getenv(key)
}
// Setenv sets the value of the environment variable named by the key.
// It returns an error, if any.
func Setenv(key, value string) error {
err := syscall.Setenv(key, value)
if err != nil {
return NewSyscallError("setenv", err)
}
return nil
}
// Unsetenv unsets a single environment variable.
func Unsetenv(key string) error {
return syscall.Unsetenv(key)
}
// Clearenv deletes all environment variables.
func Clearenv() {
syscall.Clearenv()
}
// Environ returns a copy of strings representing the environment,
// in the form "key=value".
func Environ() []string {
return syscall.Environ()
}
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