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1 /* getusershell.c -- Return names of valid user shells. |
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2 Copyright (C) 1991 Free Software Foundation, Inc. |
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3 |
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4 This program is free software; you can redistribute it and/or modify |
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5 it under the terms of the GNU General Public License as published by |
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6 the Free Software Foundation; either version 2, or (at your option) |
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7 any later version. |
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8 |
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9 This program is distributed in the hope that it will be useful, |
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10 but WITHOUT ANY WARRANTY; without even the implied warranty of |
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11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
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12 GNU General Public License for more details. |
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13 |
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14 You should have received a copy of the GNU General Public License |
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15 along with this program; if not, write to the Free Software |
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16 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. */ |
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17 |
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18 /* Written by David MacKenzie <djm@gnu.ai.mit.edu> */ |
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19 |
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115
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20 #ifdef HAVE_CONFIG_H |
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21 #include <config.h> |
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22 #endif |
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23 |
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9
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24 #ifndef SHELLS_FILE |
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25 /* File containing a list of nonrestricted shells, one per line. */ |
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26 #define SHELLS_FILE "/etc/shells" |
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27 #endif |
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28 |
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29 #include <stdio.h> |
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30 #include <ctype.h> |
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31 |
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32 #ifdef STDC_HEADERS |
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33 #include <stdlib.h> |
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34 #else |
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35 char *malloc (); |
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36 char *realloc (); |
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37 #endif |
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38 |
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133
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39 char *xstrdup (); |
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40 |
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41 static int readname (); |
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42 |
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43 /* List of shells to use if the shells file is missing. */ |
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44 static char const* const default_shells[] = |
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45 { |
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46 "/bin/sh", "/bin/csh", "/usr/bin/sh", "/usr/bin/csh", NULL |
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47 }; |
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48 |
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49 /* Index of the next shell in `default_shells' to return. |
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50 0 means we are not using `default_shells'. */ |
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51 static int default_index = 0; |
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52 |
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53 /* Input stream from the shells file. */ |
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54 static FILE *shellstream = NULL; |
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55 |
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56 /* Line of input from the shells file. */ |
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57 static char *line = NULL; |
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58 |
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59 /* Number of bytes allocated for `line'. */ |
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60 static int line_size = 0; |
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61 |
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62 /* Return an entry from the shells file, ignoring comment lines. |
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63 If the file doesn't exist, use the list in DEFAULT_SHELLS (above). |
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64 In any case, the returned string is in memory allocated through malloc. |
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65 Return NULL if there are no more entries. */ |
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66 |
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67 char * |
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68 getusershell () |
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69 { |
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70 if (default_index > 0) |
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71 { |
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72 if (default_shells[default_index]) |
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73 /* Not at the end of the list yet. */ |
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74 return xstrdup (default_shells[default_index++]); |
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75 return NULL; |
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76 } |
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77 |
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78 if (shellstream == NULL) |
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79 { |
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80 shellstream = fopen (SHELLS_FILE, "r"); |
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81 if (shellstream == NULL) |
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82 { |
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83 /* No shells file. Use the default list. */ |
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84 default_index = 1; |
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85 return xstrdup (default_shells[0]); |
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86 } |
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87 } |
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88 |
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89 while (readname (&line, &line_size, shellstream)) |
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90 { |
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91 if (*line != '#') |
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92 return line; |
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93 } |
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94 return NULL; /* End of file. */ |
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95 } |
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96 |
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97 /* Rewind the shells file. */ |
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98 |
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99 void |
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100 setusershell () |
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101 { |
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102 default_index = 0; |
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103 if (shellstream == NULL) |
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104 shellstream = fopen (SHELLS_FILE, "r"); |
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105 else |
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106 fseek (shellstream, 0L, 0); |
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107 } |
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108 |
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109 /* Close the shells file. */ |
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110 |
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111 void |
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112 endusershell () |
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113 { |
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114 if (shellstream) |
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115 { |
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116 fclose (shellstream); |
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117 shellstream = NULL; |
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118 } |
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119 } |
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120 |
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121 /* Allocate N bytes of memory dynamically, with error checking. */ |
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122 |
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123 static char * |
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124 xmalloc (n) |
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125 unsigned n; |
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126 { |
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127 char *p; |
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128 |
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129 p = malloc (n); |
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130 if (p == 0) |
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131 { |
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132 fprintf (stderr, "virtual memory exhausted\n"); |
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133 exit (1); |
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134 } |
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135 return p; |
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136 } |
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137 |
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138 /* Reallocate space P to size N, with error checking. */ |
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139 |
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140 static char * |
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141 xrealloc (p, n) |
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142 char *p; |
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143 unsigned n; |
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144 { |
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145 p = realloc (p, n); |
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146 if (p == 0) |
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147 { |
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148 fprintf (stderr, "virtual memory exhausted\n"); |
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149 exit (1); |
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150 } |
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151 return p; |
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152 } |
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153 |
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154 /* Read a line from STREAM, removing any newline at the end. |
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155 Place the result in *NAME, which is malloc'd |
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156 and/or realloc'd as necessary and can start out NULL, |
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157 and whose size is passed and returned in *SIZE. |
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158 |
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159 Return the number of characters placed in *NAME |
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160 if some nonempty sequence was found, otherwise 0. */ |
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161 |
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162 static int |
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163 readname (name, size, stream) |
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164 char **name; |
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165 int *size; |
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166 FILE *stream; |
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167 { |
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168 int c; |
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169 int name_index = 0; |
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170 |
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171 if (*name == NULL) |
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172 { |
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173 *size = 10; |
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174 *name = (char *) xmalloc (*size); |
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175 } |
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176 |
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177 /* Skip blank space. */ |
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178 while ((c = getc (stream)) != EOF && isspace (c)) |
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179 /* Do nothing. */ ; |
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180 |
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181 while (c != EOF && !isspace (c)) |
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182 { |
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183 (*name)[name_index++] = c; |
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184 while (name_index >= *size) |
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185 { |
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186 *size *= 2; |
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187 *name = (char *) xrealloc (*name, *size); |
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188 } |
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189 c = getc (stream); |
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190 } |
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191 (*name)[name_index] = '\0'; |
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192 return name_index; |
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193 } |
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194 |
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195 #ifdef TEST |
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196 main () |
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197 { |
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198 char *s; |
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199 |
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200 while (s = getusershell ()) |
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201 puts (s); |
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202 exit (0); |
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203 } |
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204 #endif |
