CODEWITHSUNDEEP
bashawksedgrep
Another.Chemist
Another.Chemist

Reputation: 2559

How to replace newline for a specific line number?

Good day to all,

I was wondering how to replace newline at specific line number.

So far I have done: [Linenumber=11]

sed ':a;N;$!ba;11s/\n//g'

Thanks in advance for any clue

Upvotes: 2

Views: 690

Answers (2)

jaypal singh
jaypal singh

Reputation: 77145

Well if you know the line number then it is pretty straightforward in any language: 

$ cat file
1
2
3
4
5

Using sed: 

$ sed '3{N;s/\n//;}' file
1
2
34
5

In sed, you can use a number as pattern which will signify the line number. We can enclose action inside braces so that it only takes place when the pattern is true. Here 3 stands for the line 3. Inside the brace is our action which states, N to append the next line to pattern space separated by a new line. At this time we have line 3\nline4 in our pattern space. We follow up with a simple substitution to replace the newline with nothing.

Using awk: 

$ awk 'NR==3{printf "%s", $0; next}1' file
1
2
34
5

awk also comprises of pattern action statements. Here we are using NR==3 as our pattern. NR is awk built-in variable which holds the current line number. When the line number is 3 we ask awk to do specific action. Our action is inside the braces. We use printf which explicitly requires a newline character. next allows us to move to the next line. 1 at the end is an awk idiom that triggers the default action which is to print. For all lines which do not match our pattern, we print them as is. Since it uses print it puts the newline for us.

Using perl:

$ perl -pe 'chomp if $.==3' file
1
2
34
5

With perl we use two options. -p creates an implicit while(<>) { print } loop to process each line of our file. -e tells the perl interpreter to execute the code that follows it. $. in perl holds the current line number. chomp is a built-in function which removes the trailing newline. So when our line number is 3, we ask perl to chomp the newline for us. All other lines are printed as is.

Upvotes: 6

Avinash Raj
Avinash Raj

Reputation: 174786

Through perl,

perl -pe 's/\n// if $. == 11' file

To save the changes made,

perl -i -pe 's/\n// if $. == 11' file

Example:

$ cat file
1
2
3
4

$ perl -pe 's/\n// if $. == 3' file
1
2
34

Upvotes: 2

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