Ubuntu – Adding variable text to text file by line

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

$ sed -r 's/[^_]+_([^_]+)_.*/\1/' file
ASSET-D
STRING-H
FILE-FD

Explanation

• -r Use ERE
• s/old/new/ replace old with new
• [^_]+ some characters that are not underscore
• (some chars) save some chars for later
• .* any number of any characters
• \1 the saved pattern