^
Beginning of line 行首
$
End of line 行末
.
Single Character 单个字符
*
Zero or more Occurrences 左边的字符出现0次或更多次
+
One or more Occurrence 左边的字符出现一次或更多次
？
Zero or one Occurrence 昨天的字符出现0次或1次
[]
[0-9]
The character class is nothing but a list of characters mentioned within a square bracket; this is used to match only one out of several characters.任意一位数字
[a-z] [a-Z]
Within the square bracket, you can use a hyphen you can specify a range of characters. For example, [0123456789] can be represented by [0-9], and alphabetic ranges can be specified such as [a-z],[A-Z] etc.
任意一个小写字母/大写或小写字母
[^]
^在中括号里表示“非”的意思
|
OR Operation 表示“或”
{}
{m}
Exactly M Occurrences 表示出现了m次
{m,n}
M to N Occurrences 表示出现了m到n次
AWK
awk -Fs '/pattern/ {action}' input-file
AWK exercises
打印uid在30~40范围内的用户名。
awk -F: '$3>=30 && $3<=40 {print $0}' /etc/passwd
打印第5-10行的行号和用户名
awk -F: 'NR>=5 && NR<=10 {print NR,$1}' /etc/passwd
打印奇数行
awk -F: 'NR%2==1' /etc/passwd
打印偶数行
awk -F: 'NR2%==0' /etc/passwd
打印字段数大于5的行
awk -F: 'NF>5 {print $0}' /etc/passwd
打印UID不等于GID的用户名
awk -F: '$3!=$4 {print $0}' /etc/passwd
打印没有指定shell的用户
awk -F: '$NF~ /nologin$/{print $1}' /etc/passwd
打印1..1000以内的7的倍数和包含7的数