github.com/akaros/go-akaros@v0.0.0-20181004170632-85005d477eab/src/os/env.go (about)

     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  // For example, os.ExpandEnv(s) is equivalent to os.Expand(s, os.Getenv).
    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  // Unsetenv unsets a single environment variable.
    95  func Unsetenv(key string) error {
    96  	return syscall.Unsetenv(key)
    97  }
    98  
    99  // Clearenv deletes all environment variables.
   100  func Clearenv() {
   101  	syscall.Clearenv()
   102  }
   103  
   104  // Environ returns a copy of strings representing the environment,
   105  // in the form "key=value".
   106  func Environ() []string {
   107  	return syscall.Environ()
   108  }