什么是$ {} 1-1在bash是什么意思？

我是从这里阅读剧本，并试图了解是什么怎么回事。这个函数执行更改Finder窗口的目录：

I'm reading the scripts from here and trying to understand what's going on. This function performs changing the directory of a Finder window:

function ee { 
 osascript -e 'set cwd to do shell script "pwd"'\
 -e 'tell application "Finder"'\
 -e "if (${1-1} <= (count Finder windows)) then"\
 -e "set the target of window ${1-1} to (POSIX file cwd) as string"\
 -e 'else' -e "open (POSIX file cwd) as string"\
 -e 'end if' -e 'end tell';\
};\

我假设 $ 是bash的PTED间$ P $，因为它是双引号内。我一直没能找到什么可以 {1-1} 的意思。我打在单独的测试脚本前pression却找不到从普通的差异 $ 1 。任何想法？

I'm assuming the $ is interpreted by bash, since it's inside double-quotes. I haven't been able to find what could {1-1} mean. I've played with the expression in separate test scripts but couldn't find a difference from plain $1. Any ideas?