Source file src/pkg/os/env.go

     1	// Copyright 2010 The Go Authors.  All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	// General environment variables.
     6	
     7	package os
     8	
     9	import "syscall"
    10	
    11	// Expand replaces ${var} or $var in the string based on the mapping function.
    12	// Invocations of undefined variables are replaced with the empty string.
    13	func Expand(s string, mapping func(string) string) string {
    14		buf := make([]byte, 0, 2*len(s))
    15		// ${} is all ASCII, so bytes are fine for this operation.
    16		i := 0
    17		for j := 0; j < len(s); j++ {
    18			if s[j] == '$' && j+1 < len(s) {
    19				buf = append(buf, s[i:j]...)
    20				name, w := getShellName(s[j+1:])
    21				buf = append(buf, mapping(name)...)
    22				j += w
    23				i = j + 1
    24			}
    25		}
    26		return string(buf) + s[i:]
    27	}
    28	
    29	// ExpandEnv replaces ${var} or $var in the string according to the values
    30	// of the current environment variables.  References to undefined
    31	// variables are replaced by the empty string.
    32	func ExpandEnv(s string) string {
    33		return Expand(s, Getenv)
    34	}
    35	
    36	// isSpellSpecialVar reports whether the character identifies a special
    37	// shell variable such as $*.
    38	func isShellSpecialVar(c uint8) bool {
    39		switch c {
    40		case '*', '#', '$', '@', '!', '?', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
    41			return true
    42		}
    43		return false
    44	}
    45	
    46	// isAlphaNum reports whether the byte is an ASCII letter, number, or underscore
    47	func isAlphaNum(c uint8) bool {
    48		return c == '_' || '0' <= c && c <= '9' || 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z'
    49	}
    50	
    51	// getName returns the name that begins the string and the number of bytes
    52	// consumed to extract it.  If the name is enclosed in {}, it's part of a ${}
    53	// expansion and two more bytes are needed than the length of the name.
    54	func getShellName(s string) (string, int) {
    55		switch {
    56		case s[0] == '{':
    57			if len(s) > 2 && isShellSpecialVar(s[1]) && s[2] == '}' {
    58				return s[1:2], 3
    59			}
    60			// Scan to closing brace
    61			for i := 1; i < len(s); i++ {
    62				if s[i] == '}' {
    63					return s[1:i], i + 1
    64				}
    65			}
    66			return "", 1 // Bad syntax; just eat the brace.
    67		case isShellSpecialVar(s[0]):
    68			return s[0:1], 1
    69		}
    70		// Scan alphanumerics.
    71		var i int
    72		for i = 0; i < len(s) && isAlphaNum(s[i]); i++ {
    73		}
    74		return s[:i], i
    75	}
    76	
    77	// Getenv retrieves the value of the environment variable named by the key.
    78	// It returns the value, which will be empty if the variable is not present.
    79	func Getenv(key string) string {
    80		v, _ := syscall.Getenv(key)
    81		return v
    82	}
    83	
    84	// Setenv sets the value of the environment variable named by the key.
    85	// It returns an error, if any.
    86	func Setenv(key, value string) error {
    87		err := syscall.Setenv(key, value)
    88		if err != nil {
    89			return NewSyscallError("setenv", err)
    90		}
    91		return nil
    92	}
    93	
    94	// Clearenv deletes all environment variables.
    95	func Clearenv() {
    96		syscall.Clearenv()
    97	}
    98	
    99	// Environ returns a copy of strings representing the environment,
   100	// in the form "key=value".
   101	func Environ() []string {
   102		return syscall.Environ()
   103	}