Ubuntu – How to use split file into two based on line start

Here is a bash script assuming your input file is named infile and the ranges are stored 1-per-line in a file named splits:

i=1
for range in $(< splits); do
  sed -n "$(echo "$range" | cut -f1 -d, )p" infile > "file$i"
  sed -n "$(echo "$range" | cut -f2 -d, )p" infile >> "file$i"
  ((i++))
done

This simply uses sed to print the lines specified by the ranges, and saves each result as a new file (files created are named file1 file2 file3 etc). Two invocations of sed are used to preserve the specified order of the rows.

Note that there is no format or error checking done by this simple script, and existing files named e.g. file1 will be overwritten.

A simplified alternative (courtesy of @muru) using while read and letting bash split the ranges instead of cut:

i=1
while IFS=',' read n1 n2 
do
    sed -n "$n1 p; $n2 p" infile > "file$i"
    ((i++))
done < splits

If the order of the lines in the output files is important (e.g. rows 5,4 != 4,5), then the sed bit will need to be broken up into two separate invocations similar to the first script.

If you want to use read to pass the names, and you want to delete lines that contain the names:

read deletename; sed "/$deletename/d" test.txt

then press enter and read waits for you to enter something, so type whatever you want deletename to be, for example 0, then press enter again and the sed command is executed. The contents of test.txt will appear in the terminal, but all the lines that contain 0, or whatever you typed, will be deleted from the stream (NOT from the file)

If you only want to delete the names themselves it's like this:

read deletename; sed "s/$deletename//g" test.txt

If you then type 0, then every instance of 0 will be deleted.

You can redirect (or tee) the output to a new file, or if you want to modify the file in place, use the -i flag (after testing)

read deletename; sed -i "/$deletename/d" test.txt

In this case you will see no output; the changes will be written to the file instead of displayed in the terminal (on STDOUT).

You need to use double quotes to allow parameter expansion, as single quotes will suppress it. but the most correct way, I think, although not necessary in this simple case, it to use single quotes around the other parts of the expression and quote the variable normally:

sed 's/'"$deletename"'//g' test.txt