-F отправка формы@- @ означает что данные отправляютcя как приложенный файл, а минус что отправляемые данные берутся из STDIN (в данном случае то что сгенерировалось после echoprint-codegen ./recorded.mp3 10 20), подробнее можно почитать man curl-F, --form
(HTTP) This lets curl emulate a filled-in form in which a user
has pressed the submit button. This causes curl to POST data
using the Content-Type multipart/form-data according to RFC
2388. This enables uploading of binary files etc. To force the
'content' part to be a file, prefix the file name with an @
sign. To just get the content part from a file, prefix the file
name with the symbol <. The difference between @ and < is then
that @ makes a file get attached in the post as a file upload,
while the < makes a text field and just get the contents for
that text field from a file.
Example, to send your password file to the server, where 'pass‐
word' is the name of the form-field to which /etc/passwd will be
the input:
curl -F password=@/etc/passwd www.mypasswords.com
To read content from stdin instead of a file, use - as the file‐
name. This goes for both @ and < constructs.
SELECT device .*,type.name as type_name
FROM device
JOIN type ON type.idtype = device.type
WHERE device.invn = $invnA variable-length string. M represents the maximum column length in characters. In MySQL 5.0, the range of M is 0 to 255 before MySQL 5.0.3, and 0 to 65,535 in MySQL 5.0.3 and later. The effective maximum length of a VARCHAR in MySQL 5.0.3 and later is subject to the maximum row size (65,535 bytes, which is shared among all columns) and the character set used. For example, utf8 characters can require up to three bytes per character, so a VARCHAR column that uses the utf8 character set can be declared to be a maximum of 21,844 characters. See Section D.7.4, “Limits on Table Column Count and Row Size”.dev.mysql.com/doc/refman/5.0/en/string-type-overvi...
MySQL stores VARCHAR values as a 1-byte or 2-byte length prefix plus data. The length prefix indicates the number of bytes in the value. A VARCHAR column uses one length byte if values require no more than 255 bytes, two length bytes if values may require more than 255 bytes.