linux - While 语句有助于 bash 脚本编写

Question

需要帮助理解这个脚本，我不明白-z是什么条件意味着第一行然后 -z与 "$1"在 if 语句中 这是脚本:

while [ -z "$USERNAME" ]
do
if [ -z "$1" ]
    then
        unset ans
 unset USER
 echo "What is the username you would like to add?"
 read USER
 echo "Is" $USER " the correct username? [y/n]"
 read ans
 case "$ans" in
     y|Y|yes|Yes|YES)
  USERNAME=$USER

;;

Answer 1

-z
string is null, that is, has zero length

有关 test 的完整信息在bash中

请参阅special variables了解有关 $1 的更多信息。

Arguments passed to the script from the command line [1] : $0, $1, $2, $3 . . .

$0 is the name of the script itself, $1 is the first argument