Identifying and removing null characters in UNIX

Question

I have a text file containing unwanted null characters (ASCII NUL, \0). When I try to view it in vi I see ^@ symbols, interleaved in normal text. How can I:

1. Identify which lines in the file contain null characters? I have tried grepping for \0 and \x0, but this did not work.

2. Remove the null characters? Running strings on the file cleaned it up, but I'm just wondering if this is the best way?

Answer 1

Use the following sed command for removing the null characters in a file.

sed -i 's/\x0//g' null.txt

this solution edits the file in place, important if the file is still being used. passing -i'ext' creates a backup of the original file with 'ext' suffix added.

Answer 2

I’d use tr:

tr < file-with-nulls -d '\000' > file-without-nulls

If you are wondering if input redirection in the middle of the command arguments works, it does. Most shells will recognize and deal with I/O redirection (<, >, …) anywhere in the command line, actually.