1, grep program
Linux text processing Three Musketeers have under - grep sed awk
grep: text line filtering tools
sed: text line editor (stream editor)
awk: report generator (output format of the present composition)
grep
It contains three commands: grep egrep fgrep, which are used for line mode (pattern) matching
egrep = gerp -E // use extended regular expression matching
the FAST = grep fgrep // use files matching the wildcard
* Grep default text using regular expressions to match *
grep usage:
grep [the Option] ... the PATTERN [filename]
grep's common option - the Option
- E supports the use of extended regular expression (ERE) (regexp)
-P use perl regular expression language search engine (every language of regular expression engines are not the same, even sed grep awk not the same engine used regexp)
- I ignored size
- V is selected from anti
- O output only matching content (default output is matched to the line)
--color = Auto syntax coloring
- n-line number
- W match fixed word
PATTERN-- regular expression
functions: through some special characters to represent a class character, and then to the front of the command to execute; if you use special characters meaning in itself, it needs \ escape;
Review: file wildcard (globbing)
* [] [^]?
1, character match
.? Any one character
[] any of the range of a character
[^] outside the range of any character
character class: [: digit:] [: alnum:] [: alpha:] [: lower:] [: Upper:] [: Space:] [: punct:]
2, the number of match
* matches the preceding character zero to many times
\? Matches the preceding character zero to 1
\ + Matches the preceding character 1 to n times
\ {m \} arranged in front of the character m times
A \ {. 7 \} AAAAAAA
\ {m, n \} matches the preceding character m to the n-th
\ {0, n \} matches the preceding character zero [0 to n times or not? (Not!)}
\ {M, \} matches the preceding character at least m
3, the position of the anchoring
^ anchors the first line
$ anchor end of the line
^ [[: space:]] * $ blank line
\ b anchor word The first and anchoring suffix
\> anchor suffix
\ <Anchoring the first word
\ <root \> Rooter
4, grouping
abc * abcccc abc we want as a whole
\ (\) Example: \ (abc \) * ABCABCABC abcccc
** grouping characteristics: By default, Linux system specifies the variable packet representation variables \ 1 \ 2 \ 3 ... (backward reference)
\ (\ (Beginning of autumn \) passed \), \ (Hong Kong \) is still restless. Multi-zone in illegal gatherings, \ (violence \) demonstrators vandalism, blocked roads, or laser, bricks assaulting a police officer, throwing petrol bombs, and some even openly beaten mainland tourists and reporters. With the upgrade demonstrators, encouraged "anti-chaos in Hong Kong," the forces behind the scenes is slowly emerging.
Example: \ (ab + \ (xy \) * \) where \ =. 1 + ab & \ (XY \) *, \ 2 = XY
abbbbbxyxyxyabxy
Add: extended regular expression
[standard regular expression \ can be removed]
groups: (after) the references \ 1 \ 2 \ 3 ...
or: |
Example: grep -E "(svm | vms ) "/ proc / cpuinfo // view the virtualization capabilities of the CPU
练习：
1、显示/proc/meminfo文件中大小s开头的行
grep -i "^s" /proc/meminfo
2、显示/etc/passwd文件中不以/bin/bash结尾的行
grep -v "/bin/bash$" /etc/passwd
3、显示/etc/passwd文件中UID号最大的用户的用户名
sort -n -t: -k3 /etc/passwd | tail -1 | cut -d: -f1
4、如果用户root存在，显示其默认的shell程序
grep "^root\>" /etc/passwd &> /dev/null && grep "^root\>" /etc/passwd | cut -d: -f7
id root &> /dev/null && grep "^root\>" /etc/passwd | cut -d: -f7
5、找出/etc/passwd中的两位或三位数
grep "[0-9]\{2,3\}" /etc/passwd
-w //匹配固定单词
\<[[:digit:]]\{2,3\}\>
\b[0-9]\{2,3\}\b
6、显示/etc/rc.d/rc.sysinit文件中，至少以一个空白字符开头的且后面为非空白字符的行
grep "^[[:space:]]\+.*[^[:space:]]$" /etc/rc.d/rc.sysinit
7、找出”netstat -tan”命令的结果中，以“LISTEN”后跟0、1或多个空白字符结尾的行
netstat -tan | grep "LISTEN[[:space:]]*$"
8、添加用户bash、testbash、basher以及nologin（其shell为/sbin/nologin）：而后找出/etc/passwd文件中用户名同shell名的行
useradd bash /bin/bash
useradd testbash
useradd basher
useradd -s /sbin/nologin nologin
grep "\(^[[:alnum:]]\+\>\).*\1$" /etc/passwd
9、IP地址如何匹配？
ip地址：
0-255.0-255.0-255.0-255
0-255
2 0-4 0-9 2[0-4][0-9]
2 5 0-5 25[0-5]
1 0-9 0-9 1[0-9][0-9]
0 0-9 0-9 [0-9][0-9]
0 0 0-9 [0-9]
grep -owE "((([0-9])|([1-9][0-9])|(1[0-9]{2})|(2[0-4][0-9])|(25[0-5]))[.]){3}(([0-9])|([1-9][0-9])|(1[0-9]{,2})|(2[0-4][0-9])|(25[0-5])){1}[[:space:]]"