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fileio: Read and write files in SQLite

The sqlean-fileio extension provides means to access the file system directly from SQL.

Reference • Acknowledgements • Installation and usage

Reference

Main features:

fileio_read

fileio_read(path [,offset [,limit]])

Reads the file specified by path and returns its contents as blob.

If offset > 0, seeks to that offset before reading. If offset is past the end of the file, returns zeroblob(0).

If limit > 0, limits the number of bytes read.

select fileio_write('hello.txt', 'hello world');
-- 11

select typeof(fileio_read('hello.txt'));
-- blob

select length(fileio_read('hello.txt'));
-- 11

select fileio_read('hello.txt');
-- hello world

select fileio_read('hello.txt', 6);
-- world

select fileio_read('hello.txt', 0, 5);
-- hello

fileio_scan

fileio_scan(path)

Reads the file specified by path line by line, without loading the whole file into memory.

select rowid, value, name from fileio_scan('hello.txt');
┌───────┬───────┬───────────┐
│ rowid │ value │   name    │
├───────┼───────┼───────────┤
│ 1     │ one   │ hello.txt │
│ 2     │ two   │ hello.txt │
│ 3     │ three │ hello.txt │
└───────┴───────┴───────────┘

Treats \n as a line separator.

Each row has the following columns:

  • rowid: line number starting from 1.
  • value: a line from the file.
  • name: a path to the file.

Inspired by sqlite-lines by Alex Garcia.

fileio_write

fileio_write(path, data [,perm [,mtime]])

Writes blob data to a file specified by path. Returns the number of written bytes. If an error occurs, returns NULL.

select fileio_write('hello.txt', 'hello world');
-- 11

The perm argument specifies permission bits for the file (octal 666 by default). Expects decimal value, not octal. Here are some popular values:

Octal Decimal Description
600 384 rw-------
644 420 rw-r--r--
664 436 rw-rw-r--
666 438 rw-rw-rw-
755 493 rwxr-xr-x
777 511 rwxrwxrwx 
select fileio_write('hello.txt', 'hello world', 436);
-- 11

If the optional mtime argument is present, it expects an integer — the number of seconds since the unix epoch. The modification-time of the target file is set to this value before returning.

fileio_append

fileio_append(path, str)

Appends str string to a file specified by path. Returns the number of written bytes. If an error occurs, returns NULL.

Useful for writing large datasets line by line, without loading the whole dataset into memory.

create table hello(value text);
insert into hello(value) values ('one'), ('two'), ('three');

select sum(fileio_append('hello.txt', value||char(10))) from hello;
-- 14
$ cat hello.txt
one
two
three

Using concatenation with char(10) adds \n to the end of the line.

fileio_mkdir

fileio_mkdir(path [,perm])

Creates a directory named path with permission bits perm (octal 777 by default).

select fileio_mkdir('hellodir');

fileio_symlink

fileio_symlink(src, dst)

Creates a symbolic link named dst, pointing to src.

select fileio_symlink('hello.txt', 'hello.lnk');

fileio_ls

fileio_ls(path [,recursive])

Lists files and directories as a virtual table.

List a single file specified by path:

select * from fileio_ls('hello.txt');
┌───────────┬───────┬────────────┬──────┐
│   name    │ mode  │   mtime    │ size │
├───────────┼───────┼────────────┼──────┤
│ hello.txt │ 33206 │ 1639516692 │ 11   │
└───────────┴───────┴────────────┴──────┘

List a whole directory. Lists only the direct children by default:

select * from fileio_ls('test') order by name;
┌─────────────────┬───────┬────────────┬──────┐
│      name       │ mode  │   mtime    │ size │
├─────────────────┼───────┼────────────┼──────┤
│ test            │ 16877 │ 1639514106 │ 384  │
│ test/crypto.sql │ 33188 │ 1639349274 │ 1426 │
│ test/fileio.sql │ 33188 │ 1639516282 │ 1606 │
│ test/fuzzy.sql  │ 33188 │ 1639349290 │ 2957 │
│ ...             │ ...   │ ...        │ ...  │
└─────────────────┴───────┴────────────┴──────┘

List a whole directory recursively. When recursive = true, lists all the descendants:

select * from fileio_ls('src', true);

Each row has the following columns:

  • name: Path to file or directory (text value).
  • mode: File mode (stat.st_mode, integer value).
  • mtime: Last modification time (stat.st_mtime, integer number of seconds since the epoch).
  • size: Total size in bytes (stat.st_size, integer value).

Use fileio_mode() helper function to get a human-readable representation of the mode:

select name, fileio_mode(mode) as mode from fileio_ls('test');
┌─────────────────┬──────────────┐
│      name       │     mode     │
├─────────────────┼──────────────┤
│ test            │ drwxr-xr-x   │
│ test/crypto.sq  │ -rw-r--r--   │
│ test/fileio.sql │ -rw-r--r--   │
│ test/fuzzy.sql  │ -rw-r--r--   │
│ ...             │ ...          │
└─────────────────┴──────────────┘

Parameter path is an absolute or relative pathname:

  • If the path refers to a file that does not exist — fileio_ls() returns zero rows.
  • If the path refers to a regular file or symbolic link — it returns a single row.
  • If the path refers to a directory — it returns one row for the directory and one row for each direct child. Optionally returns a row for every descendant, if recursive = true.

Backward Compatibilty

Some functions have aliases for backward compatibility:

readfile  = fileio_read
writefile = fileio_write
mkdir     = fileio_mkdir
symlink   = fileio_symlink
lsdir     = fileio_ls
lsmode    = fileio_mode

Acknowledgements

Partly based on the fileio.c by D. Richard Hipp.

Installation and usage

SQLite command-line interface:

sqlite> .load ./fileio
sqlite> select fileio_read('whatever.txt');

See How to install an extension for usage with IDE, Python, etc.

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