What does this line "BUILD_TARGET=${1:-none}" means in shell scripting? - bash

Question

I just started learning shell scripting so forgive me if this is too basic to ask here. I want to run this sh script
(https://github.com/daid/Cura/blob/SteamEngine/package.sh).
But I cant understand what this line ( BUILD_TARGET=${1:-none} ) does?
Here is the excerpt:
#!/usr/bin/env bash
set -e
set -u
# This script is to package the Cura package for Windows/Linux and Mac OS X
# This script should run under Linux and Mac OS X, as well as Windows with Cygwin.
#############################
# CONFIGURATION
#############################
##Select the build target
BUILD_TARGET=${1:-none}
#BUILD_TARGET=win32
#BUILD_TARGET=darwin
#BUILD_TARGET=debian_i386
#BUILD_TARGET=debian_amd64
#BUILD_TARGET=debian_armhf
#BUILD_TARGET=freebsd
##Do we need to create the final archive
ARCHIVE_FOR_DISTRIBUTION=1
##Which version name are we appending to the final archive
export BUILD_NAME=15.04.6
TARGET_DIR=Cura-${BUILD_NAME}-${BUILD_TARGET}
##Which versions of external programs to use
WIN_PORTABLE_PY_VERSION=2.7.2.1
When I tried to see how it works by running in Cygwin, it throws the following error,
$ bash package.sh
package.sh: line 2: $'\r': command not found
: invalid option 3: set: -
set: usage: set [-abefhkmnptuvxBCHP] [-o option-name] [--] [arg ...]
: invalid option 4: set: -
set: usage: set [-abefhkmnptuvxBCHP] [-o option-name] [--] [arg ...]
package.sh: line 5: $'\r': command not found
package.sh: line 8: $'\r': command not found
package.sh: line 12: $'\r': command not found
package.sh: line 21: $'\r': command not found
package.sh: line 27: $'\r': command not found
package.sh: line 30: $'\r': command not found
package.sh: line 48: syntax error near unexpected token `$'{\r''
'ackage.sh: line 48: `{
What I am missing in Cygwin?
Update 1 : I solved 'command not found' by converting the line endings to unix compatible ones. More can be found here, '\r': command not found - .bashrc / .bash_profile

Answer 1

$1 is the first command line argument
${1:-none} means if the first command line argument is unset or null, "none" is substituted. Otherwise, the value of the first command line argument is substituted.
For more info, check [ shell parameter expansion ].