#7 the regular expression of shell script programming

Multiple Command execution methods:

Script composition;

1.shengbang

2.#

3. Blank lines-lines with no content, only white space characters or tabs (tab)

4. Logical Judgment

Shell script Programming:

1. Execute permission to invoke the script through the path;

2. Direct implementation using the interpreter;

This article deals with tools:

Vim, VI, nano

Text Processing Three musketeers:

grep system:

grep, Egrep, Fgrep, Text Search tool, basic "pattern" for a given text fuzzy search, grep system is the default work in greedy mode;

Sed:stream Editor, stream data converter, line editor, text editing tools;

Awk:gawk,--gun awk, text Formatting tool, text Report generator, text processing programming language;

Cut, sort

grep system:

Grep

Egrep

Fgrep

Grep:global search Regular expression and print out of the line.

The global search is performed using regular expressions and the matching rows are displayed;

grep [OPTIONS] PATTERN [FILE ...]

PATTERN: Filter condition consists of regular expression meta-characters and text characters without special meanings;

Metacharacters of regular Expressions:

is interpreted as a special meaning by the regular expression engine;

Pcre (the most complete regular expression engine)--perl the regular expression engine of the language;

Basic Regular Expressions: Bre

Extended Regular expression: ere

grep: Only basic regular expressions are supported by default;

Egrep: Only extended regular expressions are supported by default;

Fgrep: The regular expression engine is not turned on by default;

Text characters:

Only those characters that have the meaning of the character's face;

Common options:

-I,--ignore-case: Ignores the case of text characters;

-V,--invert-match: inverse match; The result is a line that the pattern does not match successfully;

-C,--count: Count, statistics match all the lines of pattern;

-O,--only-matching: Turns off greedy mode, showing only what pattern can match;

-Q,--quiet,--silent: Quiet mode, do not output any matching results;

--color[=when],--colour[=when]: Highlight the contents of the matching pattern in a special color;

--color=auto

-E,--extended-regexp: extended regular expression, grep-e equivalent to Egrep

-F,--fixed-strings,--fixed-regexp:grep-f equivalent to Fgrep

-G,--basic-regexp: basic regular expression, egrep-g equivalent to grep

-P,--perl-regexp: Use Pcre (Perl common regular expression) engine;

-A num,--after-context=num: Displays the NUM line following the line that matches the pattern;

-B num,--before-context=num: Displays the NUM line in front of the line that matches the pattern;

-C num,-num,--context=num: Displays both front and back NUM lines at the same time as the line that matches the pattern is displayed;

Pattern

Regular expression meta-characters:

Basic regular Expression meta-characters:

Globbing--------A simplified version of the regular expression: []? *

Character Matching:

. : matches any single character;

[]: matches any single character within the specified range;

[^]: matches any single character that is unexpected in the specified range;

All of the following character sets can be placed in [] to match a single character;

[: Lower:]: denotes all lowercase letters;

[[: Lower:]]: Pass with any single lowercase letter;

[: Upper:]: denotes all uppercase letters;

[[: Upper:]]: Pass with any single capital letter;

[: Alpha:]: denotes all alphabetic characters;

[:d Igit:]: denotes all decimal digits; 10

[: Alnum:]: denotes all uppercase and lowercase letters and decimal digits;

[: Space:]: denotes white space characters;

[:p UNCT:]: denotes all punctuation marks;

[: Blank:]: Indicates a blank character;

[: Xdigit:]: all hexadecimal digits;

A-Z: all lowercase letters;

A-Z: all uppercase letters;

0-9: all decimal digits;

Number of matches: the character of the characters before the class can appear;

*: The preceding characters can appear any time (0 times, 1 times or more);

\?: The preceding character is optional (0 or 1 times);

\+: The preceding character appears at least once (1 or more times);

\{m\}: The preceding character must appear m times;

\{m,n\}: The preceding characters appear at least m times, at most n times; (m<n)

\{,n\}: The preceding characters appear at least 0 times, at most, n times;

\{m,\}: The characters in front of it appear at least m times, the more the more;

In a regular expression, the method of representing any character of any length:. *

Positional anchor characters:

Line anchoring:

Beginning of line anchoring: ^

End of line anchor: $

Word Anchor:

Head anchor:\< or \b

Tail anchor:\> or \b

\b: The previous version of the anchoring method, it is recommended not to use;

For the regular expression engine, the word is a practice string consisting of non-special characters;

Grouping and referencing characters:

\ (pattern\): treats all the characters that this pattern matches to as an integral whole;

In the regular expression engine value week, there are a series of built-in variables that hold all the character information within the group for the back reference; These variables are: \1,\2,\3, ...

Pattern1\ (pattern2\) pattern3\ (pattern4\ (pattern5\) \)

\1:pattern2

\2:pattern4

\3:pattern5

\1: The character that the pattern in the first set of parentheses matches to;

\2: The pattern in the second set of parentheses matches the character;

...

Please find the user account with the same UID and GID in/etc/passwd;

grep ' \ (\<[[:d igit:]]\+\>\). *\1 '/etc/passwd: Set and view password information for the user;

Or:

\|

Note: \| treats the strings of the left and right sides as a whole;

A\|american:a or American

Please find the integer value between 100-255 in the execution result of the ifconfig command;

First digit: 1 2

Second place: 0-9 0-4 5

Third place: 0-9 0-9 0-5

Ifconfig | grep ' \<1[0-9][0-9]\|2[0-4][0-9]\|25[0-5]\> '

Please find the integer value between 0-255 in the result of the ifconfig command execution.

grep [OPTIONS] [-E PATTERN |-f file] [FILE ...]

By default, only one pattern is allowed behind the grep command;

If you want to write more than one pattern during a grep search, you need to use the-e option: Each-e selection can use only one pattern as the parameter;

Write the required pattern into a file to ensure that there is only one pattern per line: We can use the-F file method to achieve multi-pattern matching;

Egrep

Egrep [OPTIONS] PATTERN [FILE ...]

Extended regular expression meta-characters:

Character Matching:

.

[]

[^]

Number of matches:

*

?

+

{m}

{M,n}

{m,}

{0,n}

Position Rivet:

^

$

\<,\b

\>,\b

Grouping and referencing:

()

\1,\2,\3, ...

Or:

|

All the characters in the Fgrep:pattern are treated as literal characters;

Other text-processing commands;

WC: Counts the number of rows, words, and bytes in a file;

WC [OPTION] ... [FILE] ...

WC [OPTION] ...--files0-from=f

-C: Only the number of bytes is displayed;

-L: Only the number of rows is displayed;

-W: Displays only the number of words;

Cut:remove sections from all line of files

Files that can be trimmed by the cut command are usually text documents with a certain structure or format;/etc/passwd

Cut OPTION ... [FILE] ...

-D,--delimiter=delim: Specifies the delimiter to be relied upon when the pruning operation is implemented, by default the whitespace character;

-F,--fields=list: Specifies the number of the field according to the defined delimiter;

How to use address delimitation:

#: Select a single field to be specified;

#,#: Discrete number of individual fields specified;

#-#: Multiple specified fields in succession;

--output-delimiter=string: Specifies the output symbol;

Awk:pattern scanning and processing language

Awk-f "delimiter" ' [/pattern/]{print $1,$2,... $NF} ' file ...

-F "delimiter": Specifies the field delimiter, which defaults to a blank character;

$1,$2,... $NF: The fragments of text cut from the field delimiter are stored in the corresponding internal variables;

Sort:sort lines of the text files, the default collation is the sequence of characters in the ASCII table, which is sorted by line,

This sorting criterion can be modified;

Sort [OPTION] ... [FILE] ...

Sort [OPTION] ...--files0-from=f

-R,--reverse: reverse order

-R,--random-sort: Random ordering, this stochastic algorithm is very primitive, not suitable for complex environment;

-U,--unique: Repeated rows, leaving only one row, (continuous and identical rows are called duplicates) to remove weight;

-N,--numeric-sort: The numeric value of the size of the order;

-T,--field-separator=sep: Specifies the field delimiter;

-K,--key=keydef: Indicates which key field to sort by, both general and-T are used simultaneously;

Uniq:report or omit repeated lines

Uniq [OPTION] ... [INPUT [OUTPUT]]

-D,--repeated: Displays only the rows that appear repeatedly, and each group of repeating rows displays only one row;

-U,--unique: Displays only rows that are not duplicates;

-C,--count: The number of repetitions of repeated rows is displayed in the prefix of each line;

Diff:compare Files line by line

diff [OPTION] ... FILES

Different modified versions of the same file: patching;

Patch:apply Changes to Files

Patch [-blnr][-c|-e|-n][-d dir][-d define][-i Patchfile]

[-O outfile] [-P num] [-R Rejectfile] [File]

#7 the regular expression of shell script programming