Example of using regular expressions for Linux learning-grep

Using grep with regular expressions on Linux can produce a powerful search effect, because regular expressions contain more special characters, so when combined with grep it is best to enclose the expression in single quotes to avoid errors. First create a file RegExp.txt with the following text content:

--------TEXT BEGIN-------------good morining TEACHERHELLP world is as Scriptgold sunshine looks beautifulgolden time files God Belss mewhat a delicious foodthey teast goodyou fell gladwrong word goooodwrong word g10dwrong word g12dwrong word g13 Dwww.helloworld.com[email protected]upper case 100% means purephp has GD module----------TEXT END-------------

Use "^" to match the beginning of the line:

#搜索以good开头的行grep ' ^good ' RegExp.txt

Match end of line with "$"

#搜索以Good结尾的行grep ' good$ ' RegExp.txt

Use the "^$" combination to match blank lines, and the following command calculates how many empty lines are in the file

#搜索空行的行数grep-C ' ^$ ' RegExp.txt

Use square brackets to match multiple possibilities

#搜索包含Good和good的行grep ' [Gg]ood ' RegExp.txt

Use ^ in square brackets to reverse the selection

#搜索一个包含ood的行, but cannot be good or good# remember that using angle brackets in square brackets means "not" grep ' [^gg]ood ' RegExp.txt

Use the "." No.

#搜索包含一个词, the word begins with G, followed by two arbitrary characters, followed by a D's line grep ' G. d ' RegExp.txt

#搜索包含一个词, the word begins with G or G, followed by two arbitrary characters, followed by a D's line grep ' [Gg]. d ' RegExp.txt

#搜索这样一些行, the line contains a word that satisfies the following criteria: #1. The first character can be either G or g#2. The second character can be either L or o#3. The third character can be any character except the newline. The fourth character must be Dgrep ' [gg][lo].d ' RegExp.txt

Use exact match

#搜索含有gold的行 # found in search results golden also matches out grep ' Gold ' RegExp.txt

#正如上例所示, general search, want to search for a row containing gold, found that golden also matches the # now needs to precisely match the line that contains the word "\<gold\>" RegExp.txt

#用 \b Effect and "\<\>" consistent grep ' \bgold\b ' RegExp.txt

Use the "*" number

#搜索这样一些行, the line contains a word that satisfies the following criteria: #1. Start with G #2.g followed by 0 to infinity o#3.0 to Infinity O back with dgrep go*d RegExp.txt

Use "*." No.

#1. Starting with G #2.g there must be a character. Finally, Dgrep ' G.*d ' RegExp.txt

Use the "-" sign

#文件中有一些拼写错误的单词, found that the O-letter in the Glod is written in the number 0, grep ' g1[0-9]d ' RegExp.txt

Use "\" to do character escapes

#搜索文件中包含域名www. Helloworld.com's line #从搜索的结果来看, here's "." is parsed as any character except for a newline # to use this point only as a character point, you need to use the escape character grep ' www.helloworld.com ' RegExp.txt

#这里将点做转义, the result of the output satisfies the expected grep ' www\.helloworld\.com ' RegExp.txt

Use the "\{\}" number

#文档中有一个单词good被拼写错了, wrote a few more o# search with the letter G beginning with two more O words grep ' go\{2,\} ' RegExp.txt

#搜索以字母g开头, the middle exactly contains 4 o words grep ' go\{4\} ' RegExp.txt

Special POSIX characters

#grep支持一些特殊的POSIX字符, for example #[:alnum:] literal numeric character #[:alpha:] literal character #[:d igit:] Numeric character #[:graph:] non-null character (non-whitespace, control character) #[:lower:]    lowercase characters #[:cntrl;] Control character #[:p rint:] non-null characters (including spaces) #[:p unct:] punctuation #[:space:] All whitespace characters (new lines, spaces, tabs) #[:upper:] Uppercase character #[:xdigit:] hexadecimal digits (0-9,a- F,A-F) #搜索以大写字母开头的行grep ^[[:upper:]] RegExp.txt

#搜索以数字开头的行grep ^[[:d igit:] RegExp.txt

Using the extended regular expression egrep

#搜索g和d之间至少有一个0的行 # "+" stands for matching the preceding characters more than 1 times (including once) Egrep ' Go+d ' RegExp.txt

#搜索g和d之间只有0个或者1个o的行 (0 or 1 times) # "? "Represents a match for the preceding character 1 times above egrep ' Go?d ' RegExp.txt

#搜索glad或gold的行egrep ' Glad|gold ' RegExp.txt

#搜索有glad或者gold的行的另外一种写法egrep ' G (la|ol) d ' RegExp.txt

Example of using regular expressions for Linux learning-grep