sed command in UNIX

sed command in UNIX

sed  (Stream Editor):

To convert/replace the character or string , to print the expected lines in the output and more :

Let's create  a file named fileName1 with below contents :

This fruit is Red.

sunday is weekend.

fruit and vegetable are healthy.

We have work on week days.

This is my  town.

sed  -e   's/This/That/g'   fileName1 --- converts all the "This" to That from the file fileName1.

or

sed  -e   's/This/That/'   fileName1   --- This will convert  first occurance only from each line.

Output:

That fruit is Red.

sunday is weekend.

fruit and vegetable are healthy.

We have work on week days.

That is my  town.

echo  This  This  This  This | sed  -e  's/This/That/'  ---- This command will replace the first occurance of the word "This" from the line , if more than one line exits then 1st occurance from each line.

Output:

That This This This

echo  This  This  This  This | sed  -e  's/This/That/g'  ---- This command will replace all  "This" , "g" stands for "global"

Output:

That That That That

echo  This  This  This  This | sed  -e  's/This/That/2'  ---- This command will replace the second occurance of the word  "This" from the line , if more than one line exits then 2nd occurance from each line.

Output:

This That This This

Let's take the  file : fileName1:

This fruit is Red.

sunday is weekend.

fruit and vegetable are healthy.

We have work on week days.

This is my  town.

sed   -e  's/s/S/'   fileName1   --- replaces all the first occurance of "s" from each line to "S"

Output:

ThiS fruit is Red.

Sunday is weekend.

fruit and vegetable are healthy.

We have work on week dayS.

ThiS is my  town.

sed   -e   's/e/E/g'   fileName1  ---- replaces all "e" to "E"

This fruit is REd.

sunday is wEEkEnd.

fruit and vEgEtablE arE hEalthy.

WE havE work on wEEk days.

This is my  town.

echo  We are enjoying the weekend. | sed   -e   's/e/E/5g'   --- make changes from 5th occurance  from the line , if more than one line exits then from 5th occurance in  each line.

Output:

We are enjoying the wEEkEnd.

Divert the sed output  to a file , if the output file exits, it appends. If the output file does not exit, then it creates.

echo   Seven days in a week | sed   's/Seven/7/g'   >  sedFile.txt

No output will be displayed.

Lets  open the file sedFile.txt :

7 days in a week

sed   '4 s/e/E/'    fileName1   --- replace "e" with  "E"  , first occurance on 4th line only.

Output:

This fruit is Red.

 sunday is weekend.

fruit and vegetable are healthy.

WE have work on week days.

This is my  town.

sed   '4  s/e/E/g'    fileName1  --- replace all "e" with  "E"  on 4th line only.

Output:

This fruit is Red.

sunday is weekend.

fruit and vegetable are healthy.

WE havE work on wEEk days.

This is my  town.

sed    '2 , 4 s/e/EE/g'   fileName1  --- replace "e" with "EE"  from lines 2, 3, 4 .

This fruit is Red.

sunday is wEEEEkEEnd.

fruit and vEEgEEtablEE arEE hEEalthy.

WEE havEE work on wEEEEk days.

This is my  town.

sed   '3 , $   s/h/HH/g'   fileName1  --- --- replace "h" with "HH"  from line 3 to  last  line.

This fruit is Red.

sunday is weekend.

fruit and vegetable are HHealtHHy.

We HHave work on week days.

THHis is my  town.

sed   -n  3p  fileName1  --- prints only 3rd line.

fruit and vegetable are healthy.

sed   -n   2,4p   fileName1  ---  prints lines 2 to 4, ie, 2, 3, 4

sunday is weekend.

fruit and vegetable are healthy.

We have work on week days.

sed   -n   '2,$p'   fileName1  ---  prints lines 2 to last.

sed   4p  fileName1  ---  prints line 4 twice

This fruit is Red.

sunday is weekend.

fruit and vegetable are healthy.

We have work on week days.

We have work on week days.

This is my  town.

sed -e  's/week/WWWW/p'  fileName1  --- prints the affected lines twice.

This fruit is Red.

sunday is WWWWend.

sunday is WWWWend.

fruit and vegetable are healthy.

We have work on WWWW days.

We have work on WWWW days.

This is my  town.

sed -n  's/h/H/p'  fileName1   --- prints affected lines only.

THis fruit is Red.

fruit and vegetable are Healthy.

We Have work on week days.

THis is my  town.

sed  -i  's/t/TTT/ '  --- when used  "i"   like this , the sed command  makes changes  inside the file , does not  print the  output.

sed   -i    's/t/TTT/'   fileName1  --- does not show the output, let's see inside the file :

cat fileName1

This fruiTTT is Red.

sunday is weekend.

fruiTTT and vegetable are healthy.

We have work on week days.

This is my  TTTown.

sed  -e  's/t/WW/gi'  fileName1   --- using "i"  like this, you can apply the expected change irrespective of the case , "i" removes the case sensitivity in this case.

WWhis fruiWW is Red.

sunday is weekend.

fruiWW and vegeWWable are healWWhy.

We have work on week days.

WWhis is my  WWown.

sed  3d   fileName1   ---  deletes  3rd  line  from the  output  not from the file.

This fruit is Red.

sunday is weekend.

We have work on week days.

This is my  town.

sed  $d   fileName1   ---  deletes  last  line  from the  output  not from the file.

sed  '3,$d'   fileName1   ---  deletes  3rd  to last line  from the  output  not from the file.

Let's update fileName1 , blank/empty  lines have been added as below :

This fruit is Red.

sunday is weekend.

fruit and vegetable are healthy.

We have work on week days.

This is my  town.

sed   's/^$/**Empty Line**/g'  fileName1   ---   inserts  the given text in the empty lines.

This fruit is Red.

sunday is weekend.

**Empty Line**

fruit and vegetable are healthy.

**Empty Line**

We have work on week days.

This is my  town.

Let's create  a new file : fileName2  with below contents:

This this Theese thys  this

thes that ssys this gum iss ssyy

ssa thya syha this this ibm this shss sbss

sed  -e  's/this//g'  fileName2  --- deletes the given word in the output

This  Theese thys  

thes that ssys  gum iss ssyy

ssa thya syha   ibm  shss sbss