1 | .\" Copyright (c) 1992, 1993, 1994 Henry Spencer.
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2 | .\" Copyright (c) 1992, 1993, 1994
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3 | .\" The Regents of the University of California. All rights reserved.
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4 | .\"
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5 | .\" This code is derived from software contributed to Berkeley by
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6 | .\" Henry Spencer.
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7 | .\"
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8 | .\" Redistribution and use in source and binary forms, with or without
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9 | .\" modification, are permitted provided that the following conditions
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10 | .\" are met:
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11 | .\" 1. Redistributions of source code must retain the above copyright
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12 | .\" notice, this list of conditions and the following disclaimer.
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13 | .\" 2. Redistributions in binary form must reproduce the above copyright
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14 | .\" notice, this list of conditions and the following disclaimer in the
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15 | .\" documentation and/or other materials provided with the distribution.
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16 | .\" 3. All advertising materials mentioning features or use of this software
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17 | .\" must display the following acknowledgement:
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18 | .\" This product includes software developed by the University of
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19 | .\" California, Berkeley and its contributors.
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20 | .\" 4. Neither the name of the University nor the names of its contributors
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21 | .\" may be used to endorse or promote products derived from this software
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22 | .\" without specific prior written permission.
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23 | .\"
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24 | .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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25 | .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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26 | .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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27 | .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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28 | .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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29 | .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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30 | .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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31 | .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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32 | .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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33 | .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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34 | .\" SUCH DAMAGE.
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35 | .\"
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36 | .\" @(#)regex.3 8.4 (Berkeley) 3/20/94
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37 | .\"
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38 | .TH REGEX 3 "March 20, 1994"
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39 | .de ZR
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40 | .\" one other place knows this name: the SEE ALSO section
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41 | .BR re_format (7) \\$1
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42 | ..
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43 | .SH NAME
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44 | regex, regcomp, regexec, regerror, regfree \- regular-expression library
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45 | .SH SYNOPSIS
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46 | .ft B
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47 | .\".na
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48 | #include <sys/types.h>
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49 | .br
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50 | #include <regex.h>
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51 | .sp
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52 | .in +.5i
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53 | .ti -.5i
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54 | int regcomp(regex_t *\fIpreg\fP, const char *\fIpattern\fP, int \fIcflags\fP);
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55 | .ti -.5i
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56 | int regexec(const regex_t *\fIpreg\fP, const char *\fIstring\fP,
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57 | size_t \fInmatch\fP, regmatch_t \fIpmatch\fP[], int \fIeflags\fP);
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58 | .ti -.5i
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59 | size_t regerror(int \fIerrcode\fP, const regex_t *\fIpreg\fP,
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60 | char *\fIerrbuf\fP, size_t \fIerrbuf_size\fP);
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61 | .ti -.5i
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62 | void regfree(regex_t *\fIpreg\fP);
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63 | .in -.5i
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64 | .ft R
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65 | .SH DESCRIPTION
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66 | These routines implement POSIX 1003.2 regular expressions (``RE''s);
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67 | see
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68 | .ZR .
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69 | .B Regcomp
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70 | compiles an RE written as a string into an internal form,
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71 | .B regexec
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72 | matches that internal form against a string and reports results,
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73 | .B regerror
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74 | transforms error codes from either into human-readable messages,
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75 | and
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76 | .B regfree
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77 | frees any dynamically-allocated storage used by the internal form
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78 | of an RE.
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79 | .PP
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80 | The header
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81 | .I <regex.h>
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82 | declares two structure types,
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83 | .B regex_t
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84 | and
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85 | .BR regmatch_t ,
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86 | the former for compiled internal forms and the latter for match reporting.
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87 | It also declares the four functions,
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88 | a type
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89 | .BR regoff_t ,
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90 | and a number of constants with names starting with ``REG_''.
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91 | .PP
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92 | .B Regcomp
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93 | compiles the regular expression contained in the
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94 | .I pattern
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95 | string,
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96 | subject to the flags in
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97 | .IR cflags ,
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98 | and places the results in the
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99 | .B regex_t
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100 | structure pointed to by
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101 | .IR preg .
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102 | .I Cflags
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103 | is the bitwise OR of zero or more of the following flags:
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104 | .IP REG_EXTENDED \w'REG_EXTENDED'u+2n
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105 | Compile modern (``extended'') REs,
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106 | rather than the obsolete (``basic'') REs that
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107 | are the default.
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108 | .IP REG_BASIC
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109 | This is a synonym for 0,
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110 | provided as a counterpart to REG_EXTENDED to improve readability.
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111 | .IP REG_NOSPEC
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112 | Compile with recognition of all special characters turned off.
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113 | All characters are thus considered ordinary,
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114 | so the ``RE'' is a literal string.
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115 | This is an extension,
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116 | compatible with but not specified by POSIX 1003.2,
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117 | and should be used with
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118 | caution in software intended to be portable to other systems.
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119 | REG_EXTENDED and REG_NOSPEC may not be used
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120 | in the same call to
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121 | .IR regcomp .
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122 | .IP REG_ICASE
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123 | Compile for matching that ignores upper/lower case distinctions.
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124 | See
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125 | .ZR .
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126 | .IP REG_NOSUB
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127 | Compile for matching that need only report success or failure,
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128 | not what was matched.
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129 | .IP REG_NEWLINE
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130 | Compile for newline-sensitive matching.
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131 | By default, newline is a completely ordinary character with no special
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132 | meaning in either REs or strings.
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133 | With this flag,
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134 | `[^' bracket expressions and `.' never match newline,
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135 | a `^' anchor matches the null string after any newline in the string
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136 | in addition to its normal function,
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137 | and the `$' anchor matches the null string before any newline in the
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138 | string in addition to its normal function.
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139 | .IP REG_PEND
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140 | The regular expression ends,
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141 | not at the first NUL,
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142 | but just before the character pointed to by the
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143 | .B re_endp
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144 | member of the structure pointed to by
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145 | .IR preg .
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146 | The
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147 | .B re_endp
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148 | member is of type
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149 | .BR "const\ char\ *" .
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150 | This flag permits inclusion of NULs in the RE;
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151 | they are considered ordinary characters.
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152 | This is an extension,
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153 | compatible with but not specified by POSIX 1003.2,
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154 | and should be used with
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155 | caution in software intended to be portable to other systems.
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156 | .PP
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157 | When successful,
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158 | .B regcomp
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159 | returns 0 and fills in the structure pointed to by
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160 | .IR preg .
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161 | One member of that structure
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162 | (other than
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163 | .BR re_endp )
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164 | is publicized:
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165 | .BR re_nsub ,
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166 | of type
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167 | .BR size_t ,
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168 | contains the number of parenthesized subexpressions within the RE
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169 | (except that the value of this member is undefined if the
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170 | REG_NOSUB flag was used).
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171 | If
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172 | .B regcomp
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173 | fails, it returns a non-zero error code;
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174 | see DIAGNOSTICS.
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175 | .PP
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176 | .B Regexec
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177 | matches the compiled RE pointed to by
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178 | .I preg
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179 | against the
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180 | .IR string ,
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181 | subject to the flags in
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182 | .IR eflags ,
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183 | and reports results using
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184 | .IR nmatch ,
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185 | .IR pmatch ,
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186 | and the returned value.
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187 | The RE must have been compiled by a previous invocation of
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188 | .BR regcomp .
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189 | The compiled form is not altered during execution of
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190 | .BR regexec ,
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191 | so a single compiled RE can be used simultaneously by multiple threads.
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192 | .PP
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193 | By default,
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194 | the NUL-terminated string pointed to by
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195 | .I string
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196 | is considered to be the text of an entire line, minus any terminating
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197 | newline.
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198 | The
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199 | .I eflags
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200 | argument is the bitwise OR of zero or more of the following flags:
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201 | .IP REG_NOTBOL \w'REG_STARTEND'u+2n
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202 | The first character of
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203 | the string
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204 | is not the beginning of a line, so the `^' anchor should not match before it.
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205 | This does not affect the behavior of newlines under REG_NEWLINE.
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206 | .IP REG_NOTEOL
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207 | The NUL terminating
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208 | the string
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209 | does not end a line, so the `$' anchor should not match before it.
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210 | This does not affect the behavior of newlines under REG_NEWLINE.
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211 | .IP REG_STARTEND
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212 | The string is considered to start at
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213 | \fIstring\fR\ + \fIpmatch\fR[0].\fBrm_so\fR
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214 | and to have a terminating NUL located at
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215 | \fIstring\fR\ + \fIpmatch\fR[0].\fBrm_eo\fR
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216 | (there need not actually be a NUL at that location),
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217 | regardless of the value of
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218 | .IR nmatch .
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219 | See below for the definition of
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220 | .IR pmatch
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221 | and
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222 | .IR nmatch .
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223 | This is an extension,
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224 | compatible with but not specified by POSIX 1003.2,
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225 | and should be used with
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226 | caution in software intended to be portable to other systems.
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227 | Note that a non-zero \fBrm_so\fR does not imply REG_NOTBOL;
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228 | REG_STARTEND affects only the location of the string,
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229 | not how it is matched.
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230 | .PP
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231 | See
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232 | .ZR
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233 | for a discussion of what is matched in situations where an RE or a
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234 | portion thereof could match any of several substrings of
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235 | .IR string .
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236 | .PP
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237 | Normally,
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238 | .B regexec
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239 | returns 0 for success and the non-zero code REG_NOMATCH for failure.
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240 | Other non-zero error codes may be returned in exceptional situations;
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241 | see DIAGNOSTICS.
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242 | .PP
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243 | If REG_NOSUB was specified in the compilation of the RE,
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244 | or if
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245 | .I nmatch
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246 | is 0,
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247 | .B regexec
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248 | ignores the
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249 | .I pmatch
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250 | argument (but see below for the case where REG_STARTEND is specified).
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251 | Otherwise,
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252 | .I pmatch
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253 | points to an array of
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254 | .I nmatch
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255 | structures of type
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256 | .BR regmatch_t .
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257 | Such a structure has at least the members
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258 | .B rm_so
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259 | and
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260 | .BR rm_eo ,
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261 | both of type
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262 | .B regoff_t
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263 | (a signed arithmetic type at least as large as an
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264 | .B off_t
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265 | and a
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266 | .BR ssize_t ),
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267 | containing respectively the offset of the first character of a substring
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268 | and the offset of the first character after the end of the substring.
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269 | Offsets are measured from the beginning of the
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270 | .I string
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271 | argument given to
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272 | .BR regexec .
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273 | An empty substring is denoted by equal offsets,
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274 | both indicating the character following the empty substring.
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275 | .PP
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276 | The 0th member of the
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277 | .I pmatch
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278 | array is filled in to indicate what substring of
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279 | .I string
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280 | was matched by the entire RE.
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281 | Remaining members report what substring was matched by parenthesized
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282 | subexpressions within the RE;
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283 | member
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284 | .I i
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285 | reports subexpression
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286 | .IR i ,
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287 | with subexpressions counted (starting at 1) by the order of their opening
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288 | parentheses in the RE, left to right.
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289 | Unused entries in the array\(emcorresponding either to subexpressions that
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290 | did not participate in the match at all, or to subexpressions that do not
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291 | exist in the RE (that is, \fIi\fR\ > \fIpreg\fR\->\fBre_nsub\fR)\(emhave both
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292 | .B rm_so
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293 | and
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294 | .B rm_eo
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295 | set to \-1.
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296 | If a subexpression participated in the match several times,
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297 | the reported substring is the last one it matched.
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298 | (Note, as an example in particular, that when the RE `(b*)+' matches `bbb',
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299 | the parenthesized subexpression matches each of the three `b's and then
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300 | an infinite number of empty strings following the last `b',
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301 | so the reported substring is one of the empties.)
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302 | .PP
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303 | If REG_STARTEND is specified,
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304 | .I pmatch
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305 | must point to at least one
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306 | .B regmatch_t
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307 | (even if
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308 | .I nmatch
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309 | is 0 or REG_NOSUB was specified),
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310 | to hold the input offsets for REG_STARTEND.
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311 | Use for output is still entirely controlled by
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312 | .IR nmatch ;
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313 | if
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314 | .I nmatch
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315 | is 0 or REG_NOSUB was specified,
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316 | the value of
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317 | .IR pmatch [0]
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318 | will not be changed by a successful
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319 | .BR regexec .
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320 | .PP
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321 | .B Regerror
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322 | maps a non-zero
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323 | .I errcode
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324 | from either
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325 | .B regcomp
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326 | or
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327 | .B regexec
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328 | to a human-readable, printable message.
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329 | If
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330 | .I preg
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331 | is non-NULL,
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332 | the error code should have arisen from use of
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333 | the
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334 | .B regex_t
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335 | pointed to by
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336 | .IR preg ,
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337 | and if the error code came from
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338 | .BR regcomp ,
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339 | it should have been the result from the most recent
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340 | .B regcomp
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341 | using that
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342 | .BR regex_t .
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343 | .RI ( Regerror
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344 | may be able to supply a more detailed message using information
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345 | from the
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346 | .BR regex_t .)
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347 | .B Regerror
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348 | places the NUL-terminated message into the buffer pointed to by
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349 | .IR errbuf ,
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350 | limiting the length (including the NUL) to at most
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351 | .I errbuf_size
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352 | bytes.
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353 | If the whole message won't fit,
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354 | as much of it as will fit before the terminating NUL is supplied.
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355 | In any case,
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356 | the returned value is the size of buffer needed to hold the whole
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357 | message (including terminating NUL).
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358 | If
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359 | .I errbuf_size
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360 | is 0,
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361 | .I errbuf
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362 | is ignored but the return value is still correct.
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363 | .PP
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364 | If the
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365 | .I errcode
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366 | given to
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367 | .B regerror
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368 | is first ORed with REG_ITOA,
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369 | the ``message'' that results is the printable name of the error code,
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370 | e.g. ``REG_NOMATCH'',
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371 | rather than an explanation thereof.
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372 | If
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373 | .I errcode
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374 | is REG_ATOI,
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375 | then
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376 | .I preg
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377 | shall be non-NULL and the
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378 | .B re_endp
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379 | member of the structure it points to
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380 | must point to the printable name of an error code;
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381 | in this case, the result in
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382 | .I errbuf
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383 | is the decimal digits of
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384 | the numeric value of the error code
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385 | (0 if the name is not recognized).
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386 | REG_ITOA and REG_ATOI are intended primarily as debugging facilities;
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387 | they are extensions,
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388 | compatible with but not specified by POSIX 1003.2,
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389 | and should be used with
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390 | caution in software intended to be portable to other systems.
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391 | Be warned also that they are considered experimental and changes are possible.
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392 | .PP
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393 | .B Regfree
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394 | frees any dynamically-allocated storage associated with the compiled RE
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395 | pointed to by
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396 | .IR preg .
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397 | The remaining
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398 | .B regex_t
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399 | is no longer a valid compiled RE
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400 | and the effect of supplying it to
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401 | .B regexec
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402 | or
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403 | .B regerror
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404 | is undefined.
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405 | .PP
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406 | None of these functions references global variables except for tables
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407 | of constants;
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408 | all are safe for use from multiple threads if the arguments are safe.
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409 | .SH IMPLEMENTATION CHOICES
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410 | There are a number of decisions that 1003.2 leaves up to the implementor,
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411 | either by explicitly saying ``undefined'' or by virtue of them being
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412 | forbidden by the RE grammar.
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413 | This implementation treats them as follows.
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414 | .PP
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415 | See
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416 | .ZR
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417 | for a discussion of the definition of case-independent matching.
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418 | .PP
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419 | There is no particular limit on the length of REs,
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420 | except insofar as memory is limited.
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421 | Memory usage is approximately linear in RE size, and largely insensitive
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422 | to RE complexity, except for bounded repetitions.
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423 | See BUGS for one short RE using them
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424 | that will run almost any system out of memory.
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425 | .PP
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426 | A backslashed character other than one specifically given a magic meaning
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427 | by 1003.2 (such magic meanings occur only in obsolete [``basic''] REs)
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428 | is taken as an ordinary character.
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429 | .PP
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430 | Any unmatched [ is a REG_EBRACK error.
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431 | .PP
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432 | Equivalence classes cannot begin or end bracket-expression ranges.
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433 | The endpoint of one range cannot begin another.
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434 | .PP
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435 | RE_DUP_MAX, the limit on repetition counts in bounded repetitions, is 255.
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436 | .PP
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437 | A repetition operator (?, *, +, or bounds) cannot follow another
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438 | repetition operator.
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439 | A repetition operator cannot begin an expression or subexpression
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440 | or follow `^' or `|'.
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441 | .PP
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442 | `|' cannot appear first or last in a (sub)expression or after another `|',
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443 | i.e. an operand of `|' cannot be an empty subexpression.
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444 | An empty parenthesized subexpression, `()', is legal and matches an
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445 | empty (sub)string.
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446 | An empty string is not a legal RE.
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447 | .PP
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448 | A `{' followed by a digit is considered the beginning of bounds for a
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449 | bounded repetition, which must then follow the syntax for bounds.
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450 | A `{' \fInot\fR followed by a digit is considered an ordinary character.
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451 | .PP
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452 | `^' and `$' beginning and ending subexpressions in obsolete (``basic'')
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453 | REs are anchors, not ordinary characters.
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454 | .SH SEE ALSO
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455 | .BR grep (1),
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456 | .BR re_format (7).
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457 | .PP
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458 | POSIX 1003.2, sections 2.8 (Regular Expression Notation)
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459 | and
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460 | B.5 (C Binding for Regular Expression Matching).
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461 | .SH DIAGNOSTICS
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462 | Non-zero error codes from
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463 | .B regcomp
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464 | and
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465 | .B regexec
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466 | include the following:
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467 | .PP
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468 | .nf
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469 | .ta \w'REG_ECOLLATE'u+3n
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470 | REG_NOMATCH regexec() failed to match
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471 | REG_BADPAT invalid regular expression
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472 | REG_ECOLLATE invalid collating element
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473 | REG_ECTYPE invalid character class
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474 | REG_EESCAPE \e applied to unescapable character
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475 | REG_ESUBREG invalid backreference number
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476 | REG_EBRACK brackets [ ] not balanced
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477 | REG_EPAREN parentheses ( ) not balanced
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478 | REG_EBRACE braces { } not balanced
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479 | REG_BADBR invalid repetition count(s) in { }
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480 | REG_ERANGE invalid character range in [ ]
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481 | REG_ESPACE ran out of memory
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482 | REG_BADRPT ?, *, or + operand invalid
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483 | REG_EMPTY empty (sub)expression
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484 | REG_ASSERT ``can't happen''\(emyou found a bug
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485 | REG_INVARG invalid argument, e.g. negative-length string
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486 | .fi
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487 | .SH HISTORY
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488 | Originally written by Henry Spencer.
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489 | Altered for inclusion in the 4.4BSD distribution.
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490 | .SH BUGS
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491 | This is an alpha release with known defects.
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492 | Please report problems.
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493 | .PP
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494 | There is one known functionality bug.
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495 | The implementation of internationalization is incomplete:
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496 | the locale is always assumed to be the default one of 1003.2,
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497 | and only the collating elements etc. of that locale are available.
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498 | .PP
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499 | The back-reference code is subtle and doubts linger about its correctness
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500 | in complex cases.
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501 | .PP
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502 | .B Regexec
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503 | performance is poor.
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504 | This will improve with later releases.
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505 | .I Nmatch
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506 | exceeding 0 is expensive;
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507 | .I nmatch
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508 | exceeding 1 is worse.
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509 | .B Regexec
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510 | is largely insensitive to RE complexity \fIexcept\fR that back
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511 | references are massively expensive.
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512 | RE length does matter; in particular, there is a strong speed bonus
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513 | for keeping RE length under about 30 characters,
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514 | with most special characters counting roughly double.
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515 | .PP
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516 | .B Regcomp
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517 | implements bounded repetitions by macro expansion,
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518 | which is costly in time and space if counts are large
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519 | or bounded repetitions are nested.
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520 | An RE like, say,
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521 | `((((a{1,100}){1,100}){1,100}){1,100}){1,100}'
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522 | will (eventually) run almost any existing machine out of swap space.
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523 | .PP
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524 | There are suspected problems with response to obscure error conditions.
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525 | Notably,
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526 | certain kinds of internal overflow,
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527 | produced only by truly enormous REs or by multiply nested bounded repetitions,
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528 | are probably not handled well.
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529 | .PP
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530 | Due to a mistake in 1003.2, things like `a)b' are legal REs because `)' is
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531 | a special character only in the presence of a previous unmatched `('.
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532 | This can't be fixed until the spec is fixed.
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533 | .PP
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534 | The standard's definition of back references is vague.
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535 | For example, does
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536 | `a\e(\e(b\e)*\e2\e)*d' match `abbbd'?
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537 | Until the standard is clarified,
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538 | behavior in such cases should not be relied on.
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539 | .PP
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540 | The implementation of word-boundary matching is a bit of a kludge,
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541 | and bugs may lurk in combinations of word-boundary matching and anchoring.
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