POST upload example:

post_upload.htm
===============
<html>
<body>
<form action=/cgi-bin/post_upload.cgi method=post enctype=multipart/form-data>
File to upload: <input type=file name=file1> <input type=submit>
</form>


post_upload.cgi
===============
#!/bin/sh

# POST upload format:
# -----------------------------29995809218093749221856446032^M
# Content-Disposition: form-data; name="file1"; filename="..."^M
# Content-Type: application/octet-stream^M
# ^M    <--------- headers end with empty line
# file contents
# file contents
# file contents
# ^M    <--------- extra empty line
# -----------------------------29995809218093749221856446032--^M

# Beware: bashism $'\r' is used to handle ^M

file=/tmp/$$-$RANDOM

# CGI output must start with at least empty line (or headers)
printf '\r\n'

IFS=$'\r'
read -r delim_line

IFS=''
delim_line="${delim_line}--"$'\r'

while read -r line; do
    test "$line" = '' && break
    test "$line" = $'\r' && break
done

# This will not work well for binary files: bash 3.2 is upset
# by reading NUL bytes and loses chunks of data.
# If you are not bothered by having junk appended to the uploaded file,
# consider using simple "cat >file" instead of the entire
# fragment below.

while read -r line; do

    while test "$line" = $'\r'; do
	read -r line
	test "$line" = "$delim_line" && {
	    # Aha! Empty line + delimiter! All done
	    cat <<EOF
<html>
<body>
File upload has been accepted
EOF
	    exit 0
	}
	# Empty line + NOT delimiter. Save empty line,
	# and go check next line
	printf "%s\n" $'\r' -vC >&3
    done
    # Not empty line - just save
    printf "%s\n" "$line" -vC >&3
done 3>"$file"

cat <<EOF
<html>
<body>
File upload was not terminated with '$delim_line' - ??!
EOF