[SOLVED] Inserting Text lines in a Text file that is existing via Bashscript

techjaymindave · 03-13-2017, 05:50 AM

Good day Team,

I am trying to create a script but I am stuck. The file already exists in multiple servers, and we just need to append two more lines in this file.

The below is the scenario details of this exercise.
Existing file at multiple linux machines,
Have to add Two lines in the file via bash Script
Line numbers are known, there’s no specific string to search for
And the two lines has to be in the same file in consecutive order.
Line 65 – TEXTABCD
Line 66 – TEXT DEFG

pan64 · 03-13-2017, 05:55 AM

your specification is unclear (at least for me). Would be nice to see what did you try and what do you mean by "stuck".
Looks like an easy task for awk.

Turbocapitalist · 03-13-2017, 06:08 AM

It might also be easy in sed with the i command. However, I agree, more information is needed to clarify what you need, which approach you have been trying, and how far you have gotten.

techjaymindave · 03-13-2017, 06:11 AM

Good day Pan64,

This file is a config file of a service. Let me give you an example.

# cat /etc/jay

Line1text
line2text
line3text
line4text
_____________________________________________________
That's current fine, I have to add two more lines in this same file and it should look like below:

# cat /etc/jay

Line1text
line2text
line3text
line4text
Newtextline5
Newtextline6
______________________________________________________

To do this manually at each server, is one way of doing it. However, I want to create a bashscript which can do the job by just running it at each server.

I have tried to put my brain together with SED Command, but it can edit if a string is there, but cannot insert at a specific line. Unless if you know any other way.

Thanks and regards,
Jay!

Turbocapitalist · 03-13-2017, 06:14 AM

If you want the 4th and 5th lines pushed down and 'one' and 'two' inserted, the i command in sed would be used like this:

Code:

sed -e '4ione' -e '4itwo';

This cannot append new lines though.

pan64 · 03-13-2017, 06:24 AM

Code:

sed '4iline_num_4\nline_num_5' inputfile > outfile
- or
awk ' NR==4 { print "line_num_4" } 1'

worked for me too.

techjaymindave · 03-13-2017, 06:45 AM

Good day pan64,

Can you please explain with example, how can I use those two commands as per the example mentioned above?

4iline_num_4\nline_num_5 is that a specific parameter, part of SED family?

Also, is that going to generate a new output file?

_________________________________

awk ' NR==4 { print "line_num_4" } 1'

Where do I mention the text which I want to inject into the text file if I am using awk command?

_________________________________

If I am not mistaken, you are giving two different ways to achieve the required.

Turbocapitalist · 03-13-2017, 07:40 AM

A useful, generic way is to use redirection of both input and output

Code:

sed 'somesedstuff' < input.file.txt > output.file.txt

# or

awk 'someawkstuff' < input.file.txt > output.file.txt

sundialsvcs · 03-13-2017, 10:11 AM

May I cordially suggest that you use "a real programming language" to write this script. The #!shebang facility of the shell allows you to use any language you please.

The program that you write will need to do the following:

Lock the file to ensure that no one else is doing this at the same instant.
Read the contents of the file into a memory array.
Make changes to the array.
Write the contents of the array back out to the file.
Unlock the file.

"Now, pick a language ... any [real] language."

PHP, Perl, Java, JavaScript, Ruby, Haskell, Common LISP ...

allend · 03-13-2017, 07:10 PM

If the absolute line numbers are known, then you can use a combination of head, echo and tail in conjunction with a second file.

Code:

#!/bin/bash

myfile="/file/to/update"

cp "$myfile" "$myfile.orig"

head -n 6 "$myfile.orig" > "$myfile"
echo "New line 1 here" >> "$myfile"
echo "New line 2 here" >> "$myfile"
tail -n +7 "$myfile.orig" >> "$myfile"

syg00 · 03-13-2017, 07:48 PM

Ugh. sed can handle it all.
It can insert before (as above) or after a given line. It is also aware of the last line of a file (hint).

c0wb0y · 03-14-2017, 02:45 AM

Using the line 'line4text' as point of reference, try this:

Code:

sed -i /^line4text/a\Newtextline5\nNewtextline6' /etc/jay

c0wb0y · 03-14-2017, 02:45 AM

Using the line 'line4text' as point of reference, try this:

Code:

sed -i /^line4text/a\Newtextline5\nNewtextline6' /etc/jay

pan64 · 03-14-2017, 03:02 AM

Quote:

Originally Posted by techjaymindave

Good day pan64,

Can you please explain with example, how can I use those two commands as per the example mentioned above?

4iline_num_4\nline_num_5 is that a specific parameter, part of SED family?

4 is an address, means: look for line number 4
i is a command (of sed): insert
line_num_4 is the text inserted as the new line (number 4) - can be replaced by your own text
\n is a newline
line_num_5 is the text inserted as the next new line (number 5)

Quote:

Originally Posted by techjaymindave

Also, is that going to generate a new output file?

the usual syntax is:

Code:

sed 'script' inputfile > outputfile

Quote:

Originally Posted by techjaymindave

awk ' NR==4 { print "line_num_4" } 1'

Where do I mention the text which I want to inject into the text file if I am using awk command?

in between " "

Quote:

Originally Posted by techjaymindave

If I am not mistaken, you are giving two different ways to achieve the required.

yes, one with sed, the second with awk

fatmac · 03-14-2017, 09:24 AM

Seems to me that just using the append (>>) from the command line would do it.

Code:

echo "textABC" >> nameofserverfile
echo "textDEF" >> nameofserverfile