SED Command Basics

SED command, We can do a lot of things with it but let's start with basics and let's see where we can use SED in most common places.

SED means 'Stream Editor'. when we execute a SED command the output will be redirected on to the interface so in order to save the output use a file to store the redirected results.

eg.  sed -n '1p' test.txt > test1.txt

Here p is used to print and '1' represents line no. -n used to suppress redundancy. If we use only 'p' option then all the lines will be printed twice.

--> To print the first line of the file

sed -n '1p' test.txt or sed '2,$d' test.txt

Here '2,$d' means deleting all the lines from from second line to the last line. 'd' means delete

--->To print first and last line of the file

sed  -n '1p;$p' test.txt

Here we use ';' to separate two statements. we can use any line no to print and delete just by changing line no's say sed -n '4p' test.txt will print 4th line of the file similarly for deleting also

--->To print lines between some range

sed -n '2,4p' test.txt

Here it will print all the lines from second till fourth.

---> To replace values

sed 's/aaa/bbb/g' test.txt

Here the string 'aaa' is replaced with 'bbb' in complete file. 'g' represents globally. 's' represents substitute. If we need to replace only in specific lines then sed '2,10 s/aaa/bbb/' test.txt

--->To work like GREP command

sed -n '/bbb/p' test.txt

Here will return the string it it's present. To work like grep -v command we can do in the following way

sed -n '/bbb/!p' test.txt

Here Will return all the strings which are not 'bbb'

Hope this article helps you in basic understanding of SED command