pcre
Perl Compatible Regular Expressions (or pcre) are not supported by
grep. There is a pcregrep that supports it, but traditional grep on either FreeBSD or Linux lacks support.This table compares single-letter pcre character class to POSIX names:
Description | POSIX | PCRE Single-Letter |
Word boundaries | See below list for support | \b |
Digits (0-9) | [[:digit:]] or [0-9] | \d |
Non-Digits | [^[:digit:]] or [^0-9] | \D |
Whitespace characters | [[:space:]] or [ \t\r\n\v\f] | \s |
Non-whitespace characters | [^[:space:]] or [^ \t\r\n\v\f] | \S |
Alpha-numeric and underscore | [[:alnum:]_] or [A-Za-z0-9_] | \w |
Non-word characters | [^[:alnum:]_] or [^A-Za-z0-9_] | \W |
Word boundary support:
awkcan use(^|[^_[:alnum:]]|$)grepcan use\(^\|[^_[:alnum:]]\|$\)or\(\<\|\>\)egrepandgrep -Ecan use(^|[^_[:alnum:]]|$)or(\<|\>)
In pcre, the word boundary test (
\b) works for either the left- or right-side of a word. This is different than the \< and \> word boundary sequences supported by grep which have to be used on the appropriate side of a word. This chapter focuses on pcre \b word bounding for awk . For information on \< and \> support for awk, see the previous chapter.Single-letter pcre support can be implemented in
awk for all platforms using: 1 #!/usr/bin/awk -f
2 function expand(seq)
3 {
4 return seq == "\\b" ? "(^|[^_[:alnum:]]|$)" : \
5 seq == "\\d" ? "[[:digit:]]" : \
6 seq == "\\D" ? "[^[:digit:]]" : \
7 seq == "\\s" ? "[[:space:]]" : \
8 seq == "\\S" ? "[^[:space:]]" : \
9 seq == "\\w" ? "[[:alnum:]_]" : \
10 seq == "\\W" ? "[^[:alnum:]_]" : \
11 seq
12 }
13
14 function pcre(re, head, repl, tail, rstr)
15 {
16 tail = re
17 while (match(tail, "\\\\[bdDsSwW]"))
18 {
19 head = substr(tail, 1, RSTART - 1) # text before match
20 repl = substr(tail, RSTART, RLENGTH) # match to replace
21 tail = substr(tail, RSTART + RLENGTH) # text after match
22 if ((match(head, /\\+$/) ? RLENGTH + 1 : 1) % 2 == 1)
23 repl = expand(repl)
24 rstr = rstr head repl
25 }
26 return rstr tail
27 }
28
29 # Test code for processing sample regex from stdin or file argument
30 { print $0 " -> " pcre($0) }
Last modified 2yr ago