while read silently drops a final line that has no trailing newline, and mangles backslashes without -r

The read builtin returns non-zero when it hits end of file, even if it successfully assigned a partial last line. A file or command output whose final line lacks a newline therefore has that line read into the variable and then discarded, because the loop condition is already false. Files produced by 'printf' without a trailing newline, and some HTTP responses, hit this regularly.

The idiom that handles it is 'while read -r line || [[ -n $line ]]; do ... done', which runs the body once more when read failed but left a non-empty value.

The -r flag is separately essential: without it, read treats backslash as an escape character, so a Windows path or a line ending in a backslash is silently joined with the next line. Also set IFS empty for the read, as in 'while IFS= read -r line', otherwise leading and trailing whitespace on each line is stripped. For filenames, prefer null delimiters end to end: 'find . -print0' with 'while IFS= read -r -d "" f'.