1 /* Copyright (C) 1991-2022 Free Software Foundation, Inc. 2 This file is part of the GNU C Library. 3 4 The GNU C Library is free software; you can redistribute it and/or 5 modify it under the terms of the GNU Lesser General Public 6 License as published by the Free Software Foundation; either 7 version 2.1 of the License, or (at your option) any later version. 8 9 The GNU C Library is distributed in the hope that it will be useful, 10 but WITHOUT ANY WARRANTY; without even the implied warranty of 11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 12 Lesser General Public License for more details. 13 14 You should have received a copy of the GNU Lesser General Public 15 License along with the GNU C Library; if not, see 16 <https://www.gnu.org/licenses/>. */ 17 18 #include <endian.h> 19 #include <errno.h> 20 #include <stdint.h> 21 #include <stdlib.h> 22 #include <string.h> 23 #include <unistd.h> 24 25 26 /* Return the value of the environment variable NAME. This implementation 27 is tuned a bit in that it assumes no environment variable has an empty 28 name which of course should always be true. We have a special case for 29 one character names so that for the general case we can assume at least 30 two characters which we can access. By doing this we can avoid using the 31 `strncmp' most of the time. */ 32 char * getenv(const char * name)33getenv (const char *name) 34 { 35 char **ep; 36 uint16_t name_start; 37 38 if (__environ == NULL || name[0] == '\0') 39 return NULL; 40 41 if (name[1] == '\0') 42 { 43 /* The name of the variable consists of only one character. Therefore 44 the first two characters of the environment entry are this character 45 and a '=' character. */ 46 #if __BYTE_ORDER == __LITTLE_ENDIAN || !_STRING_ARCH_unaligned 47 name_start = ('=' << 8) | *(const unsigned char *) name; 48 #else 49 name_start = '=' | ((*(const unsigned char *) name) << 8); 50 #endif 51 for (ep = __environ; *ep != NULL; ++ep) 52 { 53 #if _STRING_ARCH_unaligned 54 uint16_t ep_start = *(uint16_t *) *ep; 55 #else 56 uint16_t ep_start = (((unsigned char *) *ep)[0] 57 | (((unsigned char *) *ep)[1] << 8)); 58 #endif 59 if (name_start == ep_start) 60 return &(*ep)[2]; 61 } 62 } 63 else 64 { 65 size_t len = strlen (name); 66 #if _STRING_ARCH_unaligned 67 name_start = *(const uint16_t *) name; 68 #else 69 name_start = (((const unsigned char *) name)[0] 70 | (((const unsigned char *) name)[1] << 8)); 71 #endif 72 len -= 2; 73 name += 2; 74 75 for (ep = __environ; *ep != NULL; ++ep) 76 { 77 #if _STRING_ARCH_unaligned 78 uint16_t ep_start = *(uint16_t *) *ep; 79 #else 80 uint16_t ep_start = (((unsigned char *) *ep)[0] 81 | (((unsigned char *) *ep)[1] << 8)); 82 #endif 83 84 if (name_start == ep_start && !strncmp (*ep + 2, name, len) 85 && (*ep)[len + 2] == '=') 86 return &(*ep)[len + 3]; 87 } 88 } 89 90 return NULL; 91 } 92 libc_hidden_def (getenv) 93