Laruence's linux private house dish-Chapter 1 Regular Expression and file formatting, linux private house dish

Laruence's linux private house dish-Chapter 1 Regular Expression and file formatting, linux private house dish

12.1 what is a regular expression

A regular expression is a string processing method. It processes strings in the unit of behavior. A regular expression is assisted by some special symbols, allows you to easily find, delete, and replace a specific string.

Vi, grep, awk, and sed support regular expressions, while commands such as cp and ls can only use wildcards of bash.

 

 

12.2 basic Regular Expressions

Grep advanced parameters:

Grep [-A] [-B] [-- color = auto] 'string' filename

-A: after indicates that n rows are listed in addition to the row list.

-B: before. In addition to listing this row, the preceding n rows are also listed.

-- Color = auto: you can list the colors of the correct selected data.

 

Basic Regular Expression exercises:

Example 1: Search for a specific string

Grep-n 'regular_express.txt

Grep-vn 'the 'regular_express.txt (-v reverse selection)

Example 2: Use brackets [] to search for character sets

Grep-n't [AE] st'regular_express.txt (matching test or tast)

Grep-n '[^ g] oo' regular_express.txt (g characters are not allowed before oo)

Grep-n' [^ [: lower:] oo 'regular_express.txt ([: lower:] indicates the meaning of a-z)

Example 3: start and end of a line

Grep-n '^ test' regular_express.txt

(Note: ^ indicates "reverse selection" in [], and "outside [] indicates positioning at the beginning of the line)

Grep-n' \. $ 'regular_express.txt (find the row whose end of the trip is the decimal point)

Example 4: any character. Duplicate character *

Grep-n 'G .. d' regular_express.txt (can match characters such as good and gglad)

Grep-n 'ooo * 'regular_express.txt (matching at least two characters above o)

Grep-n 'G. * G' regular_express.txt (find the string starting with g and ending with g,. * Indicates o or multiple arbitrary characters)

Example 5: Limit the continuous RE character range {}

Grep-n 'o \ {2 \} 'regular_express.txt (find the strings of two o)

Grep-n 'go \ {2, 5 \} G' regular_express.txt (g has two to five o s, and then receives a g String)

Grep-n 'go \ {2, \} G' regular_express.txt (g has two or more o, and then a string of g)

 

Basic Regular Expression characters:

^ Word: the string to be searched (word) at the beginning of the line

Word $: string to be searched (word) at the end of a row

.: It must contain any character.

\: Escape characters to remove the special meanings of special symbols

*: Repeats the first 0 or more characters.

[List]: Find the desired character from the RE characters in the character set.

[N1-n2]: Find the range of characters to be selected from the RE Character Set

[^ List]: Find a character string or range that is not expected from the RE characters in the character set.

\ {N, m \}: The first RE character from n to m in a row. \ {n \} indicates n consecutive, \ {n, \} indicates n or more consecutive

 

Sed tool: (See sed & awk)

Format: sed [-nefr] [action]

Parameters:

-N: Quiet Mode. In general sed usage, all data from STDIN is usually listed on the screen. However, if the-n parameter is added, only the row that has been specially processed by sed will be listed.

-E: directly edit the sed action in command line mode.

-F: Write the sed action directly in a file.-f filename can execute the sed action in filename.

-R: The expanded regular expression syntax supported by sed actions

-I: directly modify the content of the file to be read, rather than the screen output.

Action Description: [n1, [n2] function

N1 and n2 may not exist, which generally indicates the number of rows selected for the action.

Function parameters:

A: new. a can be followed by strings. These strings will appear in the current next line.

I: insert, I can be followed by strings, and these strings will appear in the previous line

C: replace. c can be followed by strings. These strings can replace rows between n1 and n2.

S: replacement, which can be directly replaced. Generally, this s can be used with a regular expression.

D: delete. Because it is delete, d is usually followed by no parameters.

P: print, that is, print the selected data. Usually p runs with the sed-n parameter.

 

 

12.3 extended Regular Expressions

+: Repeat one or more previous RE characters.

? : 0 or one of the first RE characters

|: Returns the string in the OR mode.

(): Find the string of the "group" (for example, egrep-n 'G (la | oo) D' regular_express.txt indicates to find the gglad or good string)

() +: Identify multiple duplicate groups (for example, echo 'axyzxyzxyzc' | egrep 'a (xyz) + C' to find that the start is A and the end is C, there is more than one "xyz" string in the middle)

 

 

12.4 file formatting and Processing

Format and print printf:

Format: printf'print format' actual content

There are several special styles in the format:

\ A warning sound output

\ B Return key

\ F clear screen

\ N output a new row

\ R or Enter

\ T horizontal tab button

\ V vertical tab buttons

\ XNN is a two-digit string that can be converted to a character.

Common variable formats in C Language

% Ns: n indicates a number, and s indicates a string, that is, multiple characters

% Ni: n indicates a number, and I indicates interger, that is, the number of integer words.

% N. nf: n and N are both numbers. f indicates float, for example, 10 digits. The two decimal places are % 10.2f.

 

Awk tool (see sed & awk for details ):

Format: awk 'condition type 1 {Action 1} Condition Type 2 {Action 2}... 'filename

Awk is mainly used to process data in fields in each row. The default field delimiter is the Space key or tab key.

Variable:

NF: Total number of fields owned by each row ($0)

NR: currently, awk processes the "nth row" of data.

FS: the delimiter. The default Delimiter is the Space key.

Logical operators:

><>==! =

Example:

Cat/etc/passwd | awk '{FS = ":" }3 3 <10 {print $1 "\ t" $3 }'

Cat pay.txt | awk '{if (NR = 1) printf "% 10 s % 10 s, % 10s \ n", $1, $4, "Total"} NR >=2 {total = $1 + $4 printf "% 10 s % 10d % 10.2f \ n", $1, $3, total }'

 

Text comparison tool diff:

Diff is used to compare the differences between two files, and is in the unit of behavior. diff can also compare two directories.

Format: diff [-bBi] from-file to-file

-B: Ignore the difference of multiple blank spaces in a row (for example, "about me" and "about me" are considered the same)

-B: Ignore the difference between blank rows.

-I: case insensitive

Patch-pN <patch_file update

Patch-R-pN <patch_file restore

Example: Use passwd. old and passwd. new in/tmp/test to create a patch file and update old version data.

Diff-Naur passwd. old passwd. new> passwd. patch

Update the old file to the same as the new file.

Patch-p0 <passwd. patch

(Pathing file passwd. old)

Restore the content of the old file

Patch-R-p0 <passwd. patch

 

 

File print pr:

Pr/etc/man. config (print the text file man. config)

 

An example of the regular expression for Private food in linux seems to be incorrect.

I:
Grep-nv '^ $'/etc/syslog. conf
-V '^ $' indicates all rows except empty rows. -N indicates the row number displayed on each line. If you do not want to display the row number, do not use the n parameter.
For example:
Grep-v '^ $'/etc/syslog. conf

II:
In the same way, this shows all the rows except for the leading. However, because you used n and added a row number before, it is useless to take the lead instead of #, but rather a number. Or remove the n parameter.
Grep-v '^ #'

Laruence's linux private dish Chapter 1 exercise questions after class

Find/etc-size + 50 k-! -User root-exec ls-ld {}\;
Find/etc-size + 50 k-! -User root-type f-exec ls-l {}\;
Either of the above two statements is acceptable! Notice! , That! It indicates reverse selection, that is, "not a project later!

Find/etc-size + 1500 k-o-size 0
That-o is or (or) relative to-!
Reference: linux.vbird.org/