mirror of https://github.com/mkerrisk/man-pages
regex.3: Clarify details of matching
The first is that it's far from clear that the end points of the complete string match are stored in the zero'th element of the regmatch_t array; secondly, the phrase "next largest substring match" is positively misleading, implying some sort of size ordering, whereas in fact they are ordered according to their appearance in the regex pattern. Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
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man3/regex.3
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man3/regex.3
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@ -93,7 +93,7 @@ Subsequent
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searches using this pattern buffer will be case insensitive.
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searches using this pattern buffer will be case insensitive.
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.TP
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.TP
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.B REG_NOSUB
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.B REG_NOSUB
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Support for substring addressing of matches is not required.
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Do not report position of matches.
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The
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The
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.I nmatch
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.I nmatch
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and
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and
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@ -163,14 +163,26 @@ above)
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Unless
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Unless
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.B REG_NOSUB
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.B REG_NOSUB
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was set for the compilation of the pattern buffer, it is possible to
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was set for the compilation of the pattern buffer, it is possible to
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obtain substring match addressing information.
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obtain match addressing information.
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.I pmatch
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.I pmatch
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must be dimensioned to have at least
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must be dimensioned to have at least
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.I nmatch
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.I nmatch
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elements.
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elements.
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These are filled in by
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These are filled in by
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.BR regexec ()
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.BR regexec ()
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with substring match addresses.
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with substring match addresses. The offsets of the subexpression
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starting at the
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.IR i th
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open parenthesis are stored in
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.IR pmatch[i] .
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The entire regular expression's match addresses are stored in
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.IR pmatch[0] .
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(Note that to return the offsets of
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.I N
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subexpression matches,
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.I nmatch
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must be at least
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.IR N+1 .)
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Any unused structure elements will contain the value \-1.
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Any unused structure elements will contain the value \-1.
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The
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The
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