Shell脚本：在if语句中定义变量

在shell程序中，我想在if语句中定义一个月变量，如下所示。但我似乎无法在if语句中定义变量——我一直收到一条错误消息，上面写着“command'dmonth'not found.”任何帮助都将不胜感激

    #Enter date:

    echo "Enter close-out date of MONTHLY data (in the form mmdd): "
    read usedate
    echo " "

    #Extract first two digits of "usedate" to get the month number:

    dmonthn=${usedate:0:2}
    echo "month number = ${dmonthn}"
    echo " "

    #Translate the numeric month identifier into first three letters of month:

    if [ "$dmonthn" == "01" ]; then
        dmonth = 'Jan'
    elif [ "$dmonthn" == "02" ]; then 
        dmonth = "Feb" 
    elif [ "$dmonthn" == "03" ]; then 
        dmonth = "Mar" 
    elif [ "$dmonthn" == "04" ]; then 
        dmonth = "Apr" 
    elif [ "$dmonthn" == "05" ]; then 
        dmonth = "May" 
    elif [ "$dmonthn" == "06" ]; then 
        dmonth = "Jun" 
    elif [ "$dmonthn" == "07" ]; then
        dmonth = "Jul" 
    elif [ "$dmonthn" == "08" ]; then 
        dmonth = "Aug" 
    elif [ "$dmonthn" == "09" ]; then 
        dmonth = "Sep" 
    elif [ "$dmonthn" == "10" ]; then 
        dmonth = "Oct"
    elif [ "$dmonthn" == "11" ]; then 
        dmonth = "Nov"
    else 
        dmonth = "Dec" 
    fi

    echo dmonth

---

我想你在空白处遇到了麻烦。。。这在伯恩壳牌公司和它的董事会中意义重大

dmonth=“Dec”

是一个赋值，其中

dmonth=“Dec”

是一个以“=”和“Dec”为参数的命令。

正如您所知道的，在赋值中不能在

=

周围使用空格

使用

dmmonth='Jan'

代替

dmmonth='Jan'

要使代码更美观，可以使用数组并对其进行索引：

dmonthn=09
months=( Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec )
dmonth=${months[$((10#$dmonthn-1))]}
echo "$dmonth"

或案例陈述：

case $dmonthn in
  01) dmonth='Jan' ;;
  02) dmonth='Feb' ;;
  03) dmonth='Mar' ;;
  ...
esac