檢查文件是否是bash中的文本文件

我正在嘗試檢查附加到電子郵件的文件是否是文本文件，如果不是則返回錯誤。但是在測試過程中，我提供了一個有效的 text.txt 並返回“無效附件”消息。

send_email()                
{
 message=
 address=
 attachment=
 validuser=1
echo "Enter the email address: "
read address
echo ""
getent passwd | grep -q $address
if [ "$?" = "0" ]
 then
   echo -n "Enter the subject of the message: "
   read message
   echo ""

   echo "Enter the file you want to attach: "
   read attachment
   attachmenttype='file $attachment | cut -d\  -f2'
   if [ $attachmenttype = "ASCII" ]
 then 
 mail -s "$message" "$address"<"$attachment"
 press_enter
elif [ $attachmenttype = "cannot" ]
 then 
 mail -s "$message" "$address"<"$attachment"
 press_enter
else
 echo "Invalid attachment"
 press_enter
fi
else
   echo "Invalid username"
   press_enter
fi

}

代替

attachmenttype='file $attachment | cut -d\  -f2'

你應該寫：

attachmenttype=$(file "$attachment" | cut -d' ' -f2)

見http://wiki.bash-hackers.org/syntax/expansion/cmdsubst

---

或獲得mime-type：

$ file -i "$attachmenttype" | cut -d' ' -f2
text/plain;

並決定你想對文件做什麼取決於類型。

引用自：https://unix.stackexchange.com/questions/172464