231 lines
11 KiB
Markdown
231 lines
11 KiB
Markdown
<h1 align="center">SQLite Source Repository</h1>
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This repository contains the complete source code for the SQLite database
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engine. Some test scripts are also include. However, many other test scripts
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and most of the documentation are managed separately.
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If you are reading this on a Git mirror someplace, you are doing it wrong.
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The [official repository](https://www.sqlite.org/src/) is better. Go there
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now.
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## Compiling
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First create a directory in which to place
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the build products. It is recommended, but not required, that the
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build directory be separate from the source directory. Cd into the
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build directory and then from the build directory run the configure
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script found at the root of the source tree. Then run "make".
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For example:
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tar xzf sqlite.tar.gz ;# Unpack the source tree into "sqlite"
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mkdir bld ;# Build will occur in a sibling directory
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cd bld ;# Change to the build directory
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../sqlite/configure ;# Run the configure script
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make ;# Run the makefile.
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make sqlite3.c ;# Build the "amalgamation" source file
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make test ;# Run some tests (requires Tcl)
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See the makefile for additional targets.
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The configure script uses autoconf 2.61 and libtool. If the configure
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script does not work out for you, there is a generic makefile named
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"Makefile.linux-gcc" in the top directory of the source tree that you
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can copy and edit to suit your needs. Comments on the generic makefile
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show what changes are needed.
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## Using MSVC
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On Windows, all applicable build products can be compiled with MSVC.
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First open the command prompt window associated with the desired compiler
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version (e.g. "Developer Command Prompt for VS2013"). Next, use NMAKE
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with the provided "Makefile.msc" to build one of the supported targets.
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For example:
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mkdir bld
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cd bld
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nmake /f Makefile.msc TOP=..\sqlite
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nmake /f Makefile.msc sqlite3.c TOP=..\sqlite
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nmake /f Makefile.msc sqlite3.dll TOP=..\sqlite
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nmake /f Makefile.msc sqlite3.exe TOP=..\sqlite
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nmake /f Makefile.msc test TOP=..\sqlite
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There are several build options that can be set via the NMAKE command
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line. For example, to build for WinRT, simply add "FOR_WINRT=1" argument
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to the "sqlite3.dll" command line above. When debugging into the SQLite
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code, adding the "DEBUG=1" argument to one of the above command lines is
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recommended.
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SQLite does not require [Tcl](http://www.tcl.tk/) to run, but a Tcl installation
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is required by the makefiles (including those for MSVC). SQLite contains
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a lot of generated code and Tcl is used to do much of that code generation.
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The makefiles also require AWK.
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## Source Code Tour
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Most of the core source files are in the **src/** subdirectory. But
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src/ also contains files used to build the "testfixture" test harness;
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those file all begin with "test". And src/ contains the "shell.c" file
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which is the main program for the "sqlite3.exe" command-line shell and
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the "tclsqlite.c" file which implements the bindings to SQLite from the
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Tcl programming language. (Historical note: SQLite began as a Tcl
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extension and only later escaped to the wild as an independent library.)
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Test scripts and programs are found in the **test/** subdirectory.
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There are other test suites for SQLite (see
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[How SQLite Is Tested](http://www.sqlite.org/testing.html))
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but those other test suites are
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in separate source repositories.
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The **ext/** subdirectory contains code for extensions. The
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Full-text search engine is in **ext/fts3**. The R-Tree engine is in
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**ext/rtree**. The **ext/misc** subdirectory contains a number of
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smaller, single-file extensions, such as a REGEXP operator.
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The **tool/** subdirectory contains various scripts and programs used
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for building generated source code files or for testing or for generating
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accessory programs such as "sqlite3_analyzer(.exe)".
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### Generated Source Code Files
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Several of the C-language source files used by SQLite are generated from
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other sources rather than being typed in manually by a programmer. This
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section will summarize those automatically-generated files. To create all
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of the automatically-generated files, simply run "make target_source".
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The "target_source" make target will create a subdirectory "tsrc/" and
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fill it with all the source files needed to build SQLite, both
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manually-edited files and automatically-generated files.
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The SQLite interface is defined by the **sqlite3.h** header file, which is
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generated from src/sqlite.h.in, ./manifest.uuid, and ./VERSION. The
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[Tcl script](http://www.tcl.tk) at tool/mksqlite3h.tcl does the conversion.
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The manifest.uuid file contains the SHA1 hash of the particular check-in
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and is used to generate the SQLITE\_SOURCE\_ID macro. The VERSION file
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contains the current SQLite version number. The sqlite3.h header is really
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just a copy of src/sqlite.h.in with the source-id and version number inserted
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at just the right spots. Note that comment text in the sqlite3.h file is
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used to generate much of the SQLite API documentation. The Tcl scripts
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used to generate that documentation are in a separate source repository.
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The SQL language parser is **parse.c** which is generate from a grammar in
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the src/parse.y file. The conversion of "parse.y" into "parse.c" is done
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by the [lemon](./doc/lemon.html) LALR(1) parser generator. The source code
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for lemon is at tool/lemon.c. Lemon uses a
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template for generating its parser. A generic template is in tool/lempar.c,
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but SQLite uses a slightly modified template found in src/lempar.c.
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Lemon also generates the **parse.h** header file, at the same time it
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generates parse.c. But the parse.h header file is
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modified further (to add additional symbols) using the ./addopcodes.awk
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AWK script.
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The **opcodes.h** header file contains macros that define the numbers
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corresponding to opcodes in the "VDBE" virtual machine. The opcodes.h
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file is generated by the scanning the src/vdbe.c source file. The
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AWK script at ./mkopcodeh.awk does this scan and generates opcodes.h.
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A second AWK script, ./mkopcodec.awk, then scans opcodes.h to generate
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the **opcodes.c** source file, which contains a reverse mapping from
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opcode-number to opcode-name that is used for EXPLAIN output.
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The **keywordhash.h** header file contains the definition of a hash table
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that maps SQL language keywords (ex: "CREATE", "SELECT", "INDEX", etc.) into
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the numeric codes used by the parse.c parser. The keywordhash.h file is
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generated by a C-language program at tool mkkeywordhash.c.
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### The Amalgamation
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All of the individual C source code and header files (both manually-edited
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and automatically-generated) can be combined into a single big source file
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**sqlite3.c** called "the amalgamation". The amalgamation is the recommended
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way of using SQLite in a larger application. Combining all individual
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source code files into a single big source code file allows the C compiler
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to perform more cross-procedure analysis and generate better code. SQLite
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runs about 5% faster when compiled from the amalgamation versus when compiled
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from individual source files.
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The amalgamation is generated from the tool/mksqlite3c.tcl Tcl script.
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First, all of the individual source files must be gathered into the tsrc/
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subdirectory (using the equivalent of "make target_source") then the
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tool/mksqlite3c.tcl script is run to copy them all together in just the
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right order while resolving internal "#include" references.
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The amalgamation source file is more than 100K lines long. Some symbolic
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debuggers (most notably MSVC) are unable to deal with files longer than 64K
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lines. To work around this, a separate Tcl script, tool/split-sqlite3c.tcl,
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can be run on the amalgamation to break it up into a single small C file
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called **sqlite3-all.c** that does #include on about five other files
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named **sqlite3-1.c**, **sqlite3-2.c**, ..., **sqlite3-5.c**. In this way,
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all of the source code is contained within a single translation unit so
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that the compiler can do extra cross-procedure optimization, but no
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individual source file exceeds 32K lines in length.
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## How It All Fits Together
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SQLite is modular in design.
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See the [architectural description](http://www.sqlite.org/arch.html)
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for details. Other documents that are useful in
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(helping to understand how SQLite works include the
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[file format](http://www.sqlite.org/fileformat2.html) description,
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the [virtual machine](http://www.sqlite.org/vdbe.html) that runs
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prepared statements, the description of
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[how transactions work](http://www.sqlite.org/atomiccommit.html), and
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the [overview of the query planner](http://www.sqlite.org/optoverview.html).
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Unfortunately, years of effort have gone into optimizating SQLite, both
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for small size and high performance. And optimizations tend to result in
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complex code. So there is a lot of complexity in the SQLite implementation.
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Key files:
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* **sqlite.h.in** - This file defines the public interface to the SQLite
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library. Readers will need to be familiar with this interface before
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trying to understand how the library works internally.
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* **sqliteInt.h** - this header file defines many of the data objects
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used internally by SQLite.
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* **parse.y** - This file describes the LALR(1) grammer that SQLite uses
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to parse SQL statements, and the actions that are taken at each step
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in the parsing process.
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* **vdbe.c** - This file implements the virtual machine that runs
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prepared statements. There are various helper files whose names
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begin with "vdbe". The VDBE has access to the vdbeInt.h header file
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which defines internal data objects. The rest of SQLite interacts
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with the VDBE through an interface defined by vdbe.h.
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* **where.c** - This file analyzes the WHERE clause and generates
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virtual machine code to run queries efficiently. This file is
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sometimes called the "query optimizer". It has its own private
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header file, whereInt.h, that defines data objects used internally.
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* **btree.c** - This file contains the implementation of the B-Tree
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storage engine used by SQLite.
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* **pager.c** - This file contains the "pager" implementation, the
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module that implements transactions.
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* **os_unix.c** and **os_win.c** - These two files implement the interface
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between SQLite and the underlying operating system using the run-time
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pluggable VFS interface.
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* **shell.c** - This file is not part of the core SQLite library. This
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is the file that, when linked against sqlite3.a, generates the
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"sqlite3.exe" command-line shell.
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* **tclsqlite.c** - This file implements the Tcl bindings for SQLite. It
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is not part of the core SQLite library. But as most of the tests in this
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repository are written in Tcl, the Tcl language bindings are important.
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There are many other source files. Each has a suscinct header comment that
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describes its purpose and role within the larger system.
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## Contacts
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The main SQLite webpage is [http://www.sqlite.org/](http://www.sqlite.org/)
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with geographically distributed backup servers at
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[http://www2.sqlite.org/](http://www2.sqlite.org) and
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[http://www3.sqlite.org/](http://www3.sqlite.org).
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