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#This grep regex produces no output using \d for digit:
Code:
$ ip addr | egrep -i "^\d{1}"
#This grep regex produces output using [0-9] for digits:
Code:
$ ip addr | egrep -i "^[0-9]{1}"
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
2: enp3s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
3: wlp2s0b1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
4: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
5: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
What did I missed on the first egrep regex pattern?
Thank you.
If you're talking about general POSIX regex and POSIX extended regex, then there is manual page for that. There is also a manual page for the Perl regular expressions.
Code:
man 7 regex
man perlre
Both should be on your system already. The Perl pattern matching is well worth becoming familiar with, not only is it very common (often known as PCRE or Perl-Compatible Regular Expressions) but it is very, very useful.
If you're talking about general POSIX regex and POSIX extended regex, then there is manual page for that. There is also a manual page for the Perl regular expressions.
Code:
man 7 regex
man perlre
Both should be on your system already. The Perl pattern matching is well worth becoming familiar with, not only is it very common (often known as PCRE or Perl-Compatible Regular Expressions) but it is very, very useful.
On centOS 7, minimal install, I could not find it.
Code:
># man -k regex
regexp_table (5) - format of Postfix regular expression tables
Tie::Hash::NamedCapture (3pm) - Named regexp capture buffers
[root@Centos7-1024ram-minimal ~]# yum list all | grep -i regex
ant-apache-regexp.noarch 1.9.2-9.el7 base
boost-regex.i686 1.53.0-26.el7 base
boost-regex.x86_64 1.53.0-26.el7 base
perl-PPIx-Regexp.noarch 0.034-3.el7 base
perl-XML-RegExp.noarch 0.04-2.el7 base
regexp.noarch 1.5-13.el7 base
regexp-javadoc.noarch 1.5-13.el7 base
regex.7.gz is the man page itself, manpages is the name of the package - but it is on ubuntu. Looks like the name of the package on CentOS is: man-pages
regex.7.gz is the man page itself, manpages is the name of the package - but it is on ubuntu. Looks like the name of the package on CentOS is: man-pages
Thank you.
Where did you find this information locally, on your computer?
Here's a paragraph that might be relevant, from Perl's perldoc perlre: (emphasis mine)
Quote:
Unlike most locales, which are specific to a language and country pair, Unicode classifies all the characters that are letters somewhere in the world as "\w". For example, your locale might not think that "LATIN SMALL LETTER ETH" is a letter (unless you happen to speak Icelandic), but Unicode does.
Similarly, all the characters that are decimal digits somewhere in the world will match "\d"; this is hundreds, not 10, possible matches. And some of those digits look like some of the 10 ASCII digits, but mean a different number, so a human could easily think a number is a different quantity than it really is. For example, "BENGALI DIGIT FOUR" (U+09EA) looks very much like an "ASCII DIGIT EIGHT" (U+0038). And, "\d+", may match strings of digits that are a mixture from different writing systems, creating a security issue. [...] The "/a"modifier can be used to force "\d" to match just the ASCII 0 through 9.
Perl's implementation of regular expressions is a de facto standard, duplicated by most other languages, therefore this discussion should be directly relevant.
See also a discussion of so-called "POSIX bracket expressions" (N.B. not "character classes" ...) e.g. here. Particularly, in this case, [:digit:].
Last edited by sundialsvcs; 03-16-2017 at 11:18 AM.
Here's a paragraph that might be relevant, from Perl's perldoc perlre: (emphasis mine)
Perl's implementation of regular expressions is a de facto standard, duplicated by most other languages, therefore this discussion should be directly relevant.
See also a discussion of so-called "POSIX bracket expressions" (N.B. not "character classes" ...) e.g. here. Particularly, in this case, [:digit:].
Since perl is a defacto standard, does all commands
allow for perl regex?
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