How to dump a file stored in a sqlite database as a blob?

Question

I have a sqlite3 database. One column has the TEXT type, and contains blobs which I would like to save as file. Those are gzipped files.

The output of the command sqlite3 db.sqlite3 ".dump" is:

INSERT INTO "data" VALUES(1,'objects','object0.gz',X'1F8B080000000000000 [.. a few thousands of hexadecimal characters ..] F3F5EF')

How may I extract the binary data from the sqlite file to a file using the command line ?

Answer 1

sqlite3 cannot output binary data directly, so you have to convert the data to a hexdump, use cut to extract the hex digits from the blob literal, and use xxd (part of the vim package) to convert the hexdump back into binary:

sqlite3 my.db "SELECT quote(MyBlob) FROM MyTable WHERE id = 1;"  \ | cut -d\' -f2                                                   \ | xxd -r -p                                                      \ > object0.gz 

With SQLite 3.8.6 or later, the command-line shell includes the fileio extension, which implements the writefile function:

sqlite3 my.db "SELECT writefile('object0.gz', MyBlob) FROM MyTable WHERE id = 1"