Sed-Stream Editor tutorial

Sed is one of the  interesting command in Unix
Sed - Stream Editor

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sed 's/t/T/' test.txt

substitute the first occurrence of 't' with 'T' in the file test.txt and display on screen,orginal files remains unchanged

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sed 's/t/T/g' test.txt

substitute all/globally the occurrences of 't' with 'T' in the file test.txt and display on screen,orginal files remains unchanged.

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sed -i 's/t/T/g' test.txt

substitute  inline/in the file all/globally the occurrences of 't' with 'T' in the file test.txt,orginal file gets modified.

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sed 's/^t/T/g' test.txt

substitute only  the begining of the line with 't' with the 'T'

^--indicates the begining of the file

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sed 's/t$/T/g' test.txt

substitute only  the ending of the line with 't' with the 'T'

$--indicates the ending of the file

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sed 's/[0-9]/*/g' test.txt

substitute all the numbers in the file with *

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sed 's/[a-z]/*/g' test.txt


substitute all the lowercase letters in the file with *
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sed 's/[A-Z]/*/g' test.txt


substitute all the capital letters in the file with *
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SED Whole Word Match with Boundaries

sed 's/\bnew\b\old/I/g' test.txt

replaces only the word new with old in the test file

\b -means boundary

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SED Remove Lines When Match is Found

sed '/new/d' test.txt

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SED Like Head to Display Top of File

sed '5,$ d' test.txt

Deletes the lines starting from 5 to end of the file ,i.e displays only first 4 lines of the file


sed '4 q' test.txt

Display first 4 lines in the file and then quit

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SED Remove Comments From a file

sed '/^#/d' test.txt

Delete all the lines starting with #

sed '1!{/^#/d;}' test.txt

Skip line 1 and Delete all the lines starting with #

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SED print every other line

sed -n 'p;n' test.txt

print every other line(1,3,5,7),skip one line

sed -n 'p;n;n' test.txt
print every other 2 lines(1,4,7,10),skip 2 lines

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sed '=' test.txt
print line number and print the line after that

sed -n '$=' test.txt
print last line number alone ,which is nothing but the count of number of lines in a file
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