With Margo Linux (Lesson 8) awk & sed Function summary

Last Update:2015-09-23 Source: Internet

Author: User

Tags case statement

Developer on Alibaba Coud: Build your first app with APIs, SDKs, and tutorials on the Alibaba Cloud. Read more ＞

One. awk

1. What is awk

Awk is a programming language. It has the common function of the general programming language.
Because the awk language has certain characteristics, such as: using the literal translation device (interpreter) does not need to compile; Variable no type (typeless), you can use the text when the array subscript (associative array) ... and other features. Therefore, using awk to compose a program is simpler and more convenient and time-saving than using other languages. Awk also has some built-in functionality that makes awk adept at processing data with a row (Record), field type; In addition, AWK has a pipe function that can transfer processed data to external shell commands for processing, and then transfer the processed data from the shell command back to the AWK program, which makes it easy for the AWK program to use system resources.

2.awk syntax

Synopsis

awk [Options] ' program ' File File ...
awk [Options] ' pattern{action} ' file File ...

Note: The Linux version of awk is a soft link linked to gawk

Pattern: Usually use "relational expressions" (relational expression) to act as

Actions: Consists of many awk directives that comprise: print, printf

3.awk built-in variables

Variable name	Variable description
$	Whole line
$	First Field
$	A second field
NF	Number of fields
Nr	Number of rows, all files are counted in conjunction
FNR	Number of rows, each file counted
Argv	Array, save the character of the command itself
ARGC	Save the number of arguments in the awk command
FILENAME	The name of the current file being processed

Custom variables:

-V Var_name=value

Variable names are case-sensitive;

(1) Variables can be defined in program;
(2) You can customize variables by using the-v option in the command line;

4.printf

Use format for commands: printf format, item1, item2,...

(1) to specify format;
(2) will not be automatically wrapped, if you want to change the line, you need to give \ n
(3) format is used to specify its output format for each subsequent item;

The format indicator is preceded by%, followed by a character:
%c: The ASCII code that displays the characters;
%d,%i: decimal integer;
%e,%e: The scientific counting method shows the numerical value;
%f: Displays floating-point numbers;
%g,%g: Displays values in scientific notation format or floating-point number format;
%s: Display string;

%u: Displays unsigned integers;
Percent: show% itself;

Modifier:
#: Display width
-: Align Left
+: Display symbols for numeric values
. #: Value Accuracy

Cases

5.awk output Redirection

Writes the results of the awk output directly to the file

Print Items > Output-file
Print Items >> output-file

Cases
650) this.width=650; "title=" image "style=" border-top:0px;border-right:0px;background-image:none;border-bottom:0 px;padding-top:0px;padding-left:0px;border-left:0px;margin:0px;padding-right:0px; "border=" 0 "alt=" image "src=" Http://s3.51cto.com/wyfs02/M02/73/9A/wKioL1YCOMWR5NhIAAAxqQOSOag320.jpg "height="/>

6. Mode

(1) Regexp: Format is/pattern/
Only the rows that are matched to the/pattern/are processed;
(2) Expression: expressions that satisfy a condition when the result is a non-0 or a non-empty string;
Only the rows that satisfy the condition are processed;
(3) Ranges: Line range, previous address delimitation,
Nr
Processing only rows within a range
(4) Begin/end: Special mode, executed only once before the program of the awk command is run (BEGIN) or after run (END);
(5) Empty: null mode, matching any row;

Cases

Action

(1) Expressions
(2) Control statements
(3) Compound statements
(4) Input statements
(5) Output statements

8. Control statements

If-else

Format: if (condition) {then body} else {else body}

While
Format: while (condition) {while body}

Note: It is easy to create a dead loop without setting an end condition

Do-while Cycle
Format: do {Do-while body} while (condition)

For loop
Format: for (variable assignment; condition, iteration process) {for body}

Case statement
Syntax: switch (expression) {case VALUE or/rgeexp/: statement1; ... default:stementn}

Two. sed

1.sed Introduction

Sed is an online editor that processes a single line of content at a time. When processing, the currently processed rows are stored in a temporary buffer called pattern space, followed by the SED command to process the contents of the buffer, and after processing is done, the contents of the buffer are sent to the screen. Then the next line is processed, so it repeats until the end of the file. The file content does not change unless you use redirection to store the output. SED is mainly used to automatically edit one or more files, to simplify the repeated operation of the file, to write the conversion program and so on.

2.sed syntax

sed [options] ' command ' file (s)
sed [options]-F scriptfile file (s)

3. Meta Character set

^: The beginning of the anchoring line is as follows:/^sed/matches all lines beginning with sed.
$: The end of the anchor line, such as:/sed$/matches all lines ending in sed.
.: Matches a non-newline character such as:/s.d/matches the s followed by an arbitrary character followed by D.
*: Match 0 or more words such as:/*sed/match all the templates are one or more spaces followed by the SED line.
[]: matches a specified range of characters, such as/[ss]ed/matching sed and sed.
[^]: matches a character that is not within the specified range, such as:/[^a-rt-z]ed/matches a letter that does not contain a-r and t-z, immediately following the line of Ed.
$.. $: Save matching characters, such as s/\ (love\) able/\1rs,loveable is replaced with lovers.
&: Save search characters to replace other characters, such as S/love/**&**/,love, which is **love**.
\<: Anchors the beginning of a word, such as:/\<love/matches a line containing a word that begins with love.
\>: Anchors the end of a word, such as/love\>/, to match lines that contain words ending with love.
X\{m\}: Repeats characters x,m times, such as:/0\{5\}/matches rows that contain 5 O.
X\{m,\}: Repeat the character X, at least m times, such as:/o\{5,\}/matches at least 5 rows of O.
X\{m,n\}: Repeat the character X, at least m times, not more than n times, such as:/o\{5,10\}/matches rows of 5--10 O.

Find and replace text in 4.vim editing:

Address delimitation s/What to look for/replace with content/
What to look for: You can use regular expressions
Replace with: Regular expressions are not supported, but support references to the contents of the preceding regular expression groupings
Address delimitation:%, Startline,endline

5.sed working mechanism

Each time a line of text is read into "pattern space", processing is done in the pattern space, and the processing result is output to the standard output device;

-R: Supports extended regular expressions;
-N: Silent mode;
-E script1-e script2-e SCRIPT3: Specifies multiple scripts to run;
-f/path/to/script_file: Reads the script from the specified file and runs it;
-I: Directly modify the source file;

6.sed Editing commands

D Delete

s replace% for all files

I insert, edit files directly

A plus

7. Practice

(1) Remove whitespace characters from the beginning of all lines in the/boot/grub/grub.conf file;

650) this.width=650; "title=" image "style=" border-top:0px;border-right:0px;background-image:none;border-bottom:0 px;padding-top:0px;padding-left:0px;border-left:0px;margin:0px;padding-right:0px; "border=" 0 "alt=" image "src=" Http://s3.51cto.com/wyfs02/M01/73/9D/wKiom1YCOMXQ84yqAABwKbJOOwE809.jpg "height=" 129 "/>
(2) Remove all # and white space characters from the beginning of the line at the beginning of #, followed by at least one white-space character, in the/etc/fstab file;

650) this.width=650; "title=" image "style=" border-top:0px;border-right:0px;background-image:none;border-bottom:0 px;padding-top:0px;padding-left:0px;border-left:0px;margin:0px;padding-right:0px; "border=" 0 "alt=" image "src=" Http://s3.51cto.com/wyfs02/M02/73/9D/wKiom1YCOMWBJGUQAABjeW-pTNI619.jpg "height="/>
(3) Save the odd line of the/etc/fstab file as a/tmp/fstab.3;

650) this.width=650; "title=" image "style=" border-top:0px;border-right:0px;background-image:none;border-bottom:0 px;padding-top:0px;padding-left:0px;border-left:0px;margin:0px;padding-right:0px; "border=" 0 "alt=" image "src=" Http://s3.51cto.com/wyfs02/M00/73/9D/wKiom1YCOMajYsnnAABloVsv4Wg148.jpg "height=" 123 "/>
(4) Echo a file path to the SED command, take out its base name, and further, take out its path name;

With Margo Linux (Lesson 8) awk & sed Function summary

This article is an English version of an article which is originally in the Chinese language on aliyun.com and is provided for information purposes only. This website makes no representation or warranty of any kind, either expressed or implied, as to the accuracy, completeness ownership or reliability of the article or any translations thereof. If you have any concerns or complaints relating to the article, please send an email, providing a detailed description of the concern or complaint, to info-contact@alibabacloud.com. A staff member will contact you within 5 working days. Once verified, infringing content will be removed immediately.

A Free Trial That Lets You Build Big!

Start building with 50+ products and up to 12 months usage for Elastic Compute Service

Get Started for Free

Sales Support

1 on 1 presale consultation

Chat Contact Sales
After-Sales Support

24/7 Technical Support 6 Free Tickets per Quarter Faster Response

Open a Ticket
Alibaba Cloud offers highly flexible support services tailored to meet your exact needs.

Learn More