Selecting a Part of a File and Copying That into New File in Linux

how to copy lines 10 to 15 of a file into another file, in unix?

Open a terminal with a shell then

sed -n '10,15p' file1.txt > file2.txt

Simple & easy.

If you want to append to the end instead of wiping file2.txt, use >> for redirection.

sed -n '10,15p' file1.txt >> file2.txt
                          ^^

AWK is also a powerful command line text manipulator:

awk 'NR>=10 && NR<=15' file1.txt > file2.txt

How to copy the first few lines of a giant file, and add a line of text at the end of it using some Linux commands?

The head command can get the first n lines. Variations are:

head -7 file
head -n 7 file
head -7l file

which will get the first 7 lines of the file called "file". The command to use depends on your version of head. Linux will work with the first one.

To append lines to the end of the same file, use:

echo 'first line to add' >> file
echo 'second line to add' >> file
echo 'third line to add' >> file

or:

echo 'first line to add
second line to add
third line to add' >> file

to do it in one hit.

So, tying these two ideas together, if you wanted to get the first 10 lines of the input.txt file to output.txt and append a line with five "=" characters, you could use something like:

( head -10 input.txt ; echo '=====' ) > output.txt

In this case, we do both operations in a sub-shell so as to consolidate the output streams into one, which is then used to create or overwrite the output file.

How can I copy specific parts of different files in different directories and save them to open in R?

I'm not sure this is what you are looking for, but you can append to a register by using uppercase letters.
example:

in the first file, visually select the desired text. Copy to register 'a': "ay
in the following files, visually select the desired text. Append to the same register: "Ay
in the destination file, paste from said register: "ap

You can also copy/append the other ways you know from Vim. E.g.: Append the following 5 lines to register 'a': 4"Ayj, or append from within braces to register 'a': "Ayi}

Copy/Paste part of a file into another file using Terminal (or Shell)

if you know how many lines are in your source file (wc -l) you can do this .. assume 12000 lines and you want lines 2000 - 7000 in your new file (total of 5000 lines).

cat myfile | tail -10000 | head -5000 > newfile

Read the last 10k lines, then read the 1st 5k lines from that.

How to select rest of a file excluding some lines in linux?

You'd use
sed '200,700d' logfilename > destinationFilename

Reference : https://unix.stackexchange.com/questions/11204/how-do-i-remove-certain-lines-using-line-numbers-in-a-file

How to get the part of a file after the first line that matches a regular expression

The following will print the line matching TERMINATE till the end of the file:

sed -n -e '/TERMINATE/,$p'

Explained: -n disables default behavior of sed of printing each line after executing its script on it, -e indicated a script to sed, /TERMINATE/,$ is an address (line) range selection meaning the first line matching the TERMINATE regular expression (like grep) to the end of the file ($), and p is the print command which prints the current line.

This will print from the line that follows the line matching TERMINATE till the end of the file:
(from AFTER the matching line to EOF, NOT including the matching line)

sed -e '1,/TERMINATE/d'

Explained: 1,/TERMINATE/ is an address (line) range selection meaning the first line for the input to the 1st line matching the TERMINATE regular expression, and d is the delete command which delete the current line and skip to the next line. As sed default behavior is to print the lines, it will print the lines after TERMINATE to the end of input.

If you want the lines before TERMINATE:

sed -e '/TERMINATE/,$d'

And if you want both lines before and after TERMINATE in two different files in a single pass:

sed -e '1,/TERMINATE/w before
/TERMINATE/,$w after' file

The before and after files will contain the line with terminate, so to process each you need to use:

head -n -1 before
tail -n +2 after

IF you do not want to hard code the filenames in the sed script, you can:

before=before.txt
after=after.txt
sed -e "1,/TERMINATE/w $before
/TERMINATE/,\$w $after" file

But then you have to escape the $ meaning the last line so the shell will not try to expand the $w variable (note that we now use double quotes around the script instead of single quotes).

I forgot to tell that the new line is important after the filenames in the script so that sed knows that the filenames end.

How would you replace the hardcoded TERMINATE by a variable?

You would make a variable for the matching text and then do it the same way as the previous example:

matchtext=TERMINATE
before=before.txt
after=after.txt
sed -e "1,/$matchtext/w $before
/$matchtext/,\$w $after" file

to use a variable for the matching text with the previous examples:

## Print the line containing the matching text, till the end of the file:
## (from the matching line to EOF, including the matching line)
matchtext=TERMINATE
sed -n -e "/$matchtext/,\$p"

## Print from the line that follows the line containing the
## matching text, till the end of the file:
## (from AFTER the matching line to EOF, NOT including the matching line)
matchtext=TERMINATE
sed -e "1,/$matchtext/d"

## Print all the lines before the line containing the matching text:
## (from line-1 to BEFORE the matching line, NOT including the matching line)
matchtext=TERMINATE
sed -e "/$matchtext/,\$d"

The important points about replacing text with variables in these cases are:

Variables ($variablename) enclosed in single quotes ['] won't "expand" but variables inside double quotes ["] will. So, you have to change all the single quotes to double quotes if they contain text you want to replace with a variable.
The sed ranges also contain a $ and are immediately followed by a letter like: $p, $d, $w. They will also look like variables to be expanded, so you have to escape those $ characters with a backslash [\] like: \$p, \$d, \$w.