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The file name staff.txt and sample contents are:

JHON

MANAGER

10000

I want to find JHON in a file and I want to change whatever's in the 2nd line after that one with another word/number.

How can I accomplish this?

With sed you can move to next line with n:

sed '/JHON/{n;n;s/.*/42/}'

Use ed, man!

ed -s staff.txt <<< $'/JHON/+2s/.*/4242nwnq'

This calls ed in scripting mode (-s) on the staff.txt file and sends it the following commands in an ANSI-quoted here-string:

• find the line containing JHON and go two lines beyond that (+2)


• on that line, search and replace anything and everything that's there (.*) with 4242
  


• 
  write the file out to disk


• 
  quit ed

The intermediate n's separate the various ed commands.

Alternatively, you could use the c command to change the line:

ed -s staff.txt <<< $'/JHON/+2cn4242n.nwnq'

Here, the replacement text needs to be entered separately (after) the c command, and ended with a period on its own (.n).

Using awk:

awk 'f{$0="newvalue";f=0}/JHON/{print;getline;f=1}1'

f{$0="newvalue";f=0} - If f is true set line to newvalue and reset f to 0

/JHON/{print;getline;f=1} - If pattern JHON is found print it, print the next line, and set f to 1

1 - print

Yet another awk solution:

awk '/JHON/{c=0};(c!=""&&c++==2){$0="42"};{print};'

sets a counter c when JHON is found. Then, if c is set, increment and when c==2, change line ($0) to "42".

if you have only one person (one register), you can use this code:

awk '/JHON/{print $0; getline; print "SUPERVISOR"; getline; print "99999"; }' staff.txt

If you staff.txt file has many persons (many registers) and you should replace only JHON data:

awk '/.*/{if($0=="JHON"){print $0; getline; print "SUPERVISOR"; getline; print "99999"; } else {print $0;}}' staff2.txt

Example of staff2.txt:

JHON

MANAGER

10000

ROGER

TEACHER

3000

ROBERT

SCIENTIST

20000

You should get this output:

JHON

SUPERVISOR

99999

ROGER

TEACHER

3000

ROBERT

SCIENTIST

20000

Another short way, to get the same output, could be:

awk '/JHON/{print;getline; print "SUPERVISOR"; getline; $0="99999"}1' staff2.txt

Explanation: if line is JHON, print JHON, go to the next line, print SUPERVISOR, go to the next line, replace it with 99999.
if line is NOT JHON, only print it.

When I am using this command

ed -s staff.txt <<< $'/JHON/+2s/.*/4242nwnq'

Its working fine but in some case JHON word is in a Bracket [ ]
at that time this command not working properly. Its changing some another word that start with [xyz ]

example. 1)

ed -s staff.txt <<< $'/[JHON]/+2s/.*/4242nwnq'

[JHON]

[MANAGER]

[10000]

Its changing first bracket word in file not changing [JHON].