SED and regular expressions

I. Basic concepts of SED

Sed, the streaming editor, which introduces the previous program output to the SED input, is converted to another format output after a series of editing commands. The basic regular expression specification is used by default, and the extended specification is used if the-r option is added.

In the basic specification, the +,? , {}, (), | are common meanings, and if you want to use their special meanings, you need to use \ Escape, which is the opposite in the extended specification.

Sed in the processing of a line of content, the current processing of the navigation in the temporary buffer (memory), called the pattern space, and then use the SED command to process the contents of the pattern space, after processing is completed, the content to the screen (but at some point, can use to hold space to stage the data), and then repeatedly processing the next row, Until the end of the file.

Ii. Basic use of SED

(1)/pattern/p: Print matching lines

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(2)/pattern/d: Delete matching rows

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Note: The SED command does not modify the original file, only indicates that some lines do not print output, and if the plus-i option modifies the original file

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(3)/pattern/s/pattern1/pattern2/: Find the line that matches the pattern and replace the string with the first match pattern1 of the line with PATTERN2

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(4)/pattern/s/pattern1/pattern2/g: Find the line that matches the pattern and replace the string with PATTERN1 for each line matching the pattern2

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(5) addressing

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Third, regular expression

(1) ^: Beginning of Line locator

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(2) $: Line End Locator

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(3).: Matches a single character other than the line break

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(4) *: Match 0 or more preamble units

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(5) []: matches any character within a specified character group

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(6) [^]: matches any character not in the specified character group

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(7) (): Save the matched character, save as label 1, you can use \1 to refer to the

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(8) &: Save the searched string so that it is referenced in the replacement string

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(9) \<: Word head Locator

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(ten) \>: Ending locator

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(one) v\{m\}: Continuous M V

V\{m,\}: At least M v

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Iv. sed command

G: Copy The contents of the hold space into the pattern space

G: Append The contents of the hold space to the pattern space

H: copy The contents of the pattern space into the hold space

H: Append The contents of the pattern space to the hold space

D: Delete the first row in the pattern space and read in the next line

D: Delete the first row in the pattern space without reading the next line

x: swap mode space and preserve space content

V. The exercises of the SED

(1) Add a blank line to the end of each line

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(2) Simulate TAC with sed (reverse output)

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(3) Append match line to end of file

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(4) Line Column Conversions

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(5) 1+...+100

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(6) Output odd and even lines

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(7) 1+...+100 (Label method)

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Note: A means that the label A,ba means jump to the label A,$!ba means that the last line does not jump to label a.

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SED and regular expressions