Use of regular matching in grep

To match the word "computer" or "computer", you can perform the following operations: [CC] mputer "." allows matching any characters in the ASCII set, letters, or numbers. The number of times that the matching letter A appears in the matching mode is \ {\} twice and ends with B. The operation is as follows: A \ {2 \} B matches a at least 4 times, if a \ {4, \} B is used as the number of occurrences, for example, a appears twice to 4 times: when a \ {2, 4 \} B inputs string parameters in the grep command, it is best to enclose them with double quotation marks. For example, "mystring ". There are two reasons for doing this: first, to prevent being misunderstood as a shell command, and second, to search for strings consisting of multiple words, such as "jet plane ", if double quotation marks are not used, plane is mistaken for a file and the query result returns the error message "file does not exist. When you enter a string parameter in the grep command, it is best to enclose it with double quotation marks. For example, "mystring ". There are two reasons for doing this: first, to prevent being misunderstood as a shell command, and second, to search for strings consisting of multiple words, such as "jet plane ", if double quotation marks are not used, plane is mistaken for a file and the query result returns the error message "file does not exist. When you call a variable, double quotation marks should also be used, such as: grep "$ myvar" file name. Otherwise, no results will be returned. Single quotation marks should be used for invocation mode matching. A more effective method for extracting exact matching using grep is to add \> after extracting strings. Assume that 48 is extracted accurately. The method is as follows: [???] # Grep "48 \>" data. F # grep-n "48 \>" data. F # display the row number. By default, grep is case-sensitive. to query strings that are case-insensitive, you must use the-I switch. When using a regular expression, it is best to enclose it in single quotes. Suppose you want to extract the location of the city where the code is 484 and 483, # grep '48 [34] 'data. f if you want to extract a record, make it not start with 48, # grep '^ [^ 48] 'data. f extracts all codes starting with L and ending with D with 5 characters. You can use the following method: # grep 'l... d 'data. f query all records whose names start with 5 and end with 1996 or 1998 # grep '5 .. 199 [68] 'data. f The first character is any number, the second character is between 0 and 5, and the third character is between 0 and 6: # grep '[0-9] [0-5] [0-6] 'data. F # grep '^ [0-9] [0-5] [0-6] 'data. F # extract all rows that contain numbers 4 at least twice at the beginning of the row: # grep '4 \ {2, \} 'data. the fgrep command adds the-e parameter, which allows the extension mode to match. For example, to extract the city code 219 or 216, use the following method: # grep-e '2017 | 100' data. F to use ^ and $ to query empty rows. Use the-n parameter to display the actual number of rows: # grep-n '^ $ 'data. f matches special character query characters with special meanings, such as $. '"* [] ^ | \ + ?, You must add \ before a specific character \. Assume that the query contains ". ", the script is as follows: # grep '\. 'Data. F # grep '\ "'data. F to query the file name conftroll. conf (this is a configuration file). The script is as follows: # grep 'conftroll \. conf 'myfile can contain a maximum of six lower-case characters, followed by a sentence, followed by two upper-case characters # grep '[A-Z \}\. [A-Z] \ {\} 'filename. use of the wildcard * In depositgrep # grep L. * s 'testfile # matching example: "looks" # grep 'oo * 'testfile # matching example: "looks" query all rows whose end of all files contains the word device # grep' Device $ '* query the directories in the directory list, the method is as follows: # ls-L | grep '^ d: # ls-L | grep '^ [^ d: # ls-L | grep '^ d .... X .. x'

Use of regular matching in grep