This is a more modern version of this script, switching to AWS version 4 signatures that are mandatory for AWS regions created after January 2014. It also works with older regions as they seem to support the new signature format, as well.

The script's interface is a bit easier and more intuitive, too, and allows setting the access permissions, now. See the script's own help-text for information and examples on how to use it.

#!/bin/sh

usage()
{
    cat <<USAGE

Simple script uploading a file to S3. Supports AWS signature version 4, custom
region, permissions and mime-types. Uses Content-MD5 header to guarantee
uncorrupted file transfer.

Usage:
  `basename $0` aws_ak aws_sk bucket srcfile targfile [acl] [mime_type]

Where <arg> is one of:
  aws_ak     access key ('' for upload to public writable bucket)
  aws_sk     secret key ('' for upload to public writable bucket)
  bucket     bucket name (with optional @region suffix, default is us-east-1)
  srcfile    path to source file
  targfile   path to target (dir if it ends with '/', relative to bucket root)
  acl        s3 access permissions (default: public-read)
  mime_type  optional mime-type (tries to guess if omitted)

Dependencies:
  To run, this shell script depends on command-line curl and openssl, as well
  as standard Unix tools

Examples:
  To upload file '~/blog/media/image.png' to bucket 'storage' in region
  'eu-central-1' with key (path relative to bucket) 'media/image.png':

    `basename $0` ACCESS SECRET storage@eu-central-1 \\
      ~/blog/image.png media/

  To upload file '~/blog/media/image.png' to public-writable bucket 'storage'
  in default region 'us-east-1' with key (path relative to bucket) 'x/y.png':

    `basename $0` '' '' storage ~/blog/image.png x/y.png

USAGE
    exit 0
}

guessmime()
{
    mime=`file -b --mime-type $1`
    if [ "$mime" = "text/plain" ]; then
        case $1 in
            *.css)           mime=text/css;;
            *.ttf|*.otf)     mime=application/font-sfnt;;
            *.woff)          mime=application/font-woff;;
            *.woff2)         mime=font/woff2;;
            *rss*.xml|*.rss) mime=application/rss+xml;;
            *)               if head $1 | grep '<html.*>' >/dev/null; then mime=text/html; fi;;
        esac
    fi
    printf "$mime"
}

if [ $# -lt 5 ]; then usage; fi

# Inputs.
aws_ak="$1"                                                              # access key
aws_sk="$2"                                                              # secret key
bucket=`printf $3 | awk 'BEGIN{FS="@"}{print $1}'`                       # bucket name
region=`printf $3 | awk 'BEGIN{FS="@"}{print ($2==""?"us-east-1":$2)}'`  # region name
srcfile="$4"                                                             # source file
targfile=`echo -n "$5" | sed "s/\/$/\/$(basename $srcfile)/"`            # target file
acl=${6:-'public-read'}                                                  # s3 perms
mime=${7:-"`guessmime "$srcfile"`"}                                      # mime type
md5=`openssl md5 -binary "$srcfile" | openssl base64`


# Create signature if not public upload.
key_and_sig_args=''
if [ "$aws_ak" != "" ] && [ "$aws_sk" != "" ]; then

    # Need current and file upload expiration date. Handle GNU and BSD date command style to get tomorrow's date.
    date=`date -u +%Y%m%dT%H%M%SZ`
    expdate=`if ! date -v+1d +%Y-%m-%d 2>/dev/null; then date -d tomorrow +%Y-%m-%d; fi`
    expdate_s=`printf $expdate | sed s/-//g` # without dashes, as we need both formats below
    service='s3'

    # Generate policy and sign with secret key following AWS Signature version 4, below
    p=$(cat <<POLICY | openssl base64
{ "expiration": "${expdate}T12:00:00.000Z",
  "conditions": [
    {"acl": "$acl" },
    {"bucket": "$bucket" },
    ["starts-with", "\$key", ""],
    ["starts-with", "\$content-type", ""],
    ["content-length-range", 1, `ls -l -H "$srcfile" | awk '{print $5}' | head -1`],
    {"content-md5": "$md5" },
    {"x-amz-date": "$date" },
    {"x-amz-credential": "$aws_ak/$expdate_s/$region/$service/aws4_request" },
    {"x-amz-algorithm": "AWS4-HMAC-SHA256" }
  ]
}
POLICY
    )

    # AWS4-HMAC-SHA256 signature
    s=`printf "$expdate_s"   | openssl sha256 -hmac "AWS4$aws_sk"           -hex | sed 's/(stdin)= //'`
    s=`printf "$region"      | openssl sha256 -mac HMAC -macopt hexkey:"$s" -hex | sed 's/(stdin)= //'`
    s=`printf "$service"     | openssl sha256 -mac HMAC -macopt hexkey:"$s" -hex | sed 's/(stdin)= //'`
    s=`printf "aws4_request" | openssl sha256 -mac HMAC -macopt hexkey:"$s" -hex | sed 's/(stdin)= //'`
    s=`printf "$p"           | openssl sha256 -mac HMAC -macopt hexkey:"$s" -hex | sed 's/(stdin)= //'`

    key_and_sig_args="-F X-Amz-Credential=$aws_ak/$expdate_s/$region/$service/aws4_request -F X-Amz-Algorithm=AWS4-HMAC-SHA256 -F X-Amz-Signature=$s -F X-Amz-Date=${date}"
fi


# Upload. Supports anonymous upload if bucket is public-writable, and keys are set to ''.
echo "Uploading: $srcfile ($mime) to $bucket:$targfile"
curl                            \
    -# -k                       \
    -F key=$targfile            \
    -F acl=$acl                 \
    $key_and_sig_args           \
    -F "Policy=$p"              \
    -F "Content-MD5=$md5"       \
    -F "Content-Type=$mime"     \
    -F "file=@$srcfile"         \
    https://${bucket}.s3.amazonaws.com/ | cat # pipe through cat so curl displays upload progress bar, *and* response