linux-sed command Explanation

Sed is one of the most commonly used commands in operations, and it's time to take notes and record them on weekends. SED is a line-of-text editor that is processed on a per-row basis for plain ASCII code. sed when the text is processed, row-by-line content is read into memory for processing and the processing result is output. This memory space is called "pattern space" because sed does not have to be processed on every line, and some rows can be processed according to certain patterns. By default, the source file is not modified, only the data in the pattern space is processed. Prints the contents of the pattern space after processing is finished.

Sed several grammar rules:

1.sed startline,endline file

From the starting line to the end line, such as 1,100, from the first row to the line

2. Pattern Matching rows

Sed/^root/file lines starting with root

3. / mode 1/,/ mode 2/ indicates that the first time the file is matched to the line of pattern 1 to the first time by mode 2 Match to the end of the line, all the lines in the middle

4. give only one value , line number means specifying a specific row precisely

Sed 100 file   Precise handling of section 100 line ,$ sed $ file  $-1 Represents the penultimate line

5. specify the starting line, using +n, to start with the specified line , N rows backward , and a total of n+1 Line Contents

Sed 2,+10 file

Several commands commonly used in SED:

d: Delete the specified row

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from the first line, delete the backward line , deleting two rows altogether

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P: show rows that match the criteria

The following example shows that the condition is displayed two times, because the sed command also displays the contents of the pattern space by default, and the p command displays the matching rows, so there are two lines

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-N Displays only the rows that match the criteria:

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A: use a \string--- to append a new row after the specified line, with the contents of string

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to add two rows after matching a row , the string \ n wraps the line

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I \string: indicates that a new line is added before the specified line and the contents are string,\n wrapped

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R FileName: adds the contents of the specified file to the qualifying line

Add the contents of another file behind the second line,/ROOT/TT is another path to the text file

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Multi-line processing

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W FileName: Saves content in the specified range to the specified file

In the example below,/tmp/t2 is the file path

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s : s/ match mode / What to replace /    delimiters are not limited to / s# match mode # What to replace #

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The default is to replace only the first occurrence of the string in each line

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If you want to replace all the strings that match in each row, you need to use the following two parameters:

G: Global substitution

I: ignoring character capitalization when looking up

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a back reference in SED:

& represents the entire string for a reference pattern match

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Back reference:

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You must use a back reference when you reference only part of the content that matches to

If you capitalize the l character of the matched word

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Sed does not modify the source file by default, and if you need to modify the source file directly, use the-i option.

-r: sed only supports basic regularization by default ,-R enables sed to use extended regular expressions

For example, delete the white space character at the beginning of the line in the file, preceded by a white space character , and #

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Linux-sed Command Detailed