BASH’s ‘read’ built-in supports ‘\0′ as delimiter

By chys on November 25th, 2008

I thought it was impossible to use ‘’ as a delimiter in bash, but noticed yesterday that Gentoo’s ebuild.sh had pipelines like this:

find ….. -print0 |
while read -r -d $’’ x; do
# Do something with file $x
done

This makes it possible to handle any strange filenames correctly, even if the filename contains newline ('n') or carriage return ('r') characters. (Some other commands, including sort and xargs, have options to make null character the delimiter based on the same reason.)

Because BASH internally uses C-style strings, in which '' is the terminator, read -d $'' is essentially equivalent to read -d ''. This is why I believed read did not accept null-delimited strings. However, it turns out that BASH actually handles this correctly.

I checked BASH’s souce code and found the delimiter was simply determined by delim = *list_optarg; (bash-3.2/builtins/read.def, line 296) where list_optarg points to the argument following -d. Therefore, it makes no difference to the value of delim whether $'' or '' is used.