{"Entry":{"collection":"language","key":"pltclu","name":"pltclu","aliases":[],"metadata":{"aliases":[],"category":"PL/Tcl","content_hash":"978d6468963c6b1f279806e037135a9949da86234aa52b54dc3d6db189fc31ab","derived_content_hash":"9d2a546dab2ef3b923b5c43ea187fb07404575db4999c35902cd715f3a7ccf2c","imported_at":"2026-09-30T00:40:44.373921+08:00","name":"pltclu","name_zh":"","slug":"pltclu","summary":"PL/TclU untrusted procedural language"}},"Definition":{"Collection":"language","Key":"pltclu","SourceDatabase":"center","Version":"18","SourceTable":"procedural_language","SourceKey":"pltclu","SourceRevision":"555610c24d53e4316da5b7d3fc25c279d96856d5e0e23ee308c328c5fa881d9f","Facts":{"aliases":[],"attributes":{"comment":"PL/TclU untrusted procedural language","default_version":"1.0","family":"PL/Tcl","handler":"pltclu_call_handler","inline_handler":"","kind":"Bundled procedural-language variant","library":"$libdir/pltcl","module_pathname":"$libdir/pltcl","trusted":"f","validator":""},"comparison_data":{"default_version":"1.0","family":"PL/Tcl","handler":"pltclu_call_handler","inline_handler":"","kind":"Bundled procedural-language variant","library":"$libdir/pltcl","trusted":"f","validator":""},"comparison_hash":"f76f2eec7aa9560ce301885f25a023a15137ef259d3f0536f267d92fdb9f3ffe","description":["PL/TclU untrusted procedural language"],"description_zh":"过程语言 pltclu。","description_zh_html":"\u003cp\u003e过程语言 pltclu。\u003c/p\u003e\u003cdl\u003e\u003cdt\u003e运算符族\u003c/dt\u003e\u003cdd\u003e\u003ccode\u003ePL/Tcl\u003c/code\u003e\u003c/dd\u003e\u003cdt\u003e处理函数\u003c/dt\u003e\u003cdd\u003e\u003ccode\u003epltclu_call_handler\u003c/code\u003e\u003c/dd\u003e\u003cdt\u003e库\u003c/dt\u003e\u003cdd\u003e\u003ccode\u003e$libdir/pltcl\u003c/code\u003e\u003c/dd\u003e\u003cdt\u003e受信任\u003c/dt\u003e\u003cdd\u003e\u003ccode\u003e否\u003c/code\u003e\u003c/dd\u003e\u003cdt\u003e默认版本\u003c/dt\u003e\u003cdd\u003e\u003ccode\u003e1.0\u003c/code\u003e\u003c/dd\u003e\u003cdt\u003e模块路径\u003c/dt\u003e\u003cdd\u003e\u003ccode\u003e$libdir/pltcl\u003c/code\u003e\u003c/dd\u003e\u003c/dl\u003e\u003ch3\u003e同版本中文手册节选\u003c/h3\u003e\u003cp\u003e\n    PL/Tcl 提供了函数编写者在 C 语言中所具备的大部分能力，但会施加少量限制，并额外提供 Tcl 可用的强大字符串处理库。\n   \u003c/p\u003e\u003cp\u003e\n    其中一个颇具吸引力的\u003cspan class=\"emphasis\"\u003e\u003cem\u003e良性\u003c/em\u003e\u003c/span\u003e限制是，所有内容都在 Tcl 解释器的安全上下文中执行。除了安全 Tcl 受限的命令集之外，只提供了少数通过 SPI 访问数据库以及通过 \u003ccode class=\"function\"\u003eelog()\u003c/code\u003e 发出消息的命令。与 C 函数不同，PL/Tcl 不提供访问数据库服务器内部机制的方法，也不能在 \u003cspan class=\"productname\"\u003ePostgreSQL\u003c/span\u003e 服务器进程的权限下获得操作系统级访问。因此，可以信任非特权数据库用户使用这种语言；它不会授予他们无限制的权限。\n   \u003c/p\u003e\u003cp\u003e\n    另一项值得注意的实现限制是，Tcl 函数不能用来为新数据类型创建输入/输出函数。\n   \u003c/p\u003e\u003cp\u003e\n    有时需要编写不受安全 Tcl 限制的 Tcl 函数。例如，可能希望某个 Tcl 函数能够发送电子邮件。为处理这类情况，\u003cspan class=\"application\"\u003ePL/Tcl\u003c/span\u003e 提供了一个名为 \u003ccode class=\"literal\"\u003ePL/TclU\u003c/code\u003e 的变体（其中 U 表示不受信任的 Tcl）。除了使用完整的 Tcl 解释器之外，它与前者是完全相同的语言。\u003cspan class=\"emphasis\"\u003e\u003cem\u003e如果使用 \u003cspan class=\"application\"\u003ePL/TclU\u003c/span\u003e，就必须将其安装为一种不受信任的过程语言\u003c/em\u003e\u003c/span\u003e，这样就只有数据库超级用户才能在其中创建函数。\u003cspan class=\"application\"\u003ePL/TclU\u003c/span\u003e 函数的编写者必须确保该函数不会被用来做任何不希望发生的事情，因为它能够执行任何以数据库管理员身份登录的用户所能做的事情。\n   \u003c/p\u003e\u003cp\u003e\u003ca href=\"/zh/docs/18/pltcl-overview.html\"\u003e查看完整中文手册与上下文\u003c/a\u003e。\u003c/p\u003e","facts":[{"label":"Kind","value":"Bundled procedural-language variant"},{"label":"Family","value":"PL/Tcl"},{"label":"Trusted","value":"f"},{"label":"Handler","value":"pltclu_call_handler"},{"label":"Library","value":"$libdir/pltcl"},{"label":"Default version","value":"1.0"},{"label":"Module pathname","value":"$libdir/pltcl"},{"label":"Comment","value":"PL/TclU untrusted procedural language"}],"facts_zh":[{"label":"种类","value":"随源码提供的过程语言变体"},{"label":"操作符家族","value":"PL/Tcl"},{"label":"可信","value":"f"},{"label":"处理函数","value":"pltclu_call_handler"},{"label":"库","value":"$libdir/pltcl"},{"label":"默认版本","value":"1.0"},{"label":"模块路径","value":"$libdir/pltcl"},{"label":"注释","value":"PL/TclU 非可信过程语言"}],"manual_html":"\u003cdiv class=\"sect1\" id=\"PLTCL-OVERVIEW\"\u003e\n\u003cdiv class=\"titlepage\"\u003e\n\u003cdiv\u003e\n\u003cdiv\u003e\n\u003ch2 class=\"title\"\u003e42.1. Overview \u003c/h2\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003ePL/Tcl offers most of the capabilities a function writer has in the C language, with a few restrictions, and with the addition of the powerful string processing libraries that are available for Tcl.\u003c/p\u003e\n\u003cp\u003eOne compelling \u003cspan class=\"emphasis\"\u003e\u003cem\u003egood\u003c/em\u003e\u003c/span\u003e restriction is that everything is executed from within the safety of the context of a Tcl interpreter. 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In addition to the limited command set of safe Tcl, only a few commands are available to access the database via SPI and to raise messages via \u003ccode\u003eelog()\u003c/code\u003e. PL/Tcl provides no way to access internals of the database server or to gain OS-level access under the permissions of the \u003cspan\u003ePostgreSQL\u003c/span\u003e server process, as a C function can do. Thus, unprivileged database users can be trusted to use this language; it does not give them unlimited authority.\u003c/p\u003e\n\u003cp\u003eThe other notable implementation restriction is that Tcl functions cannot be used to create input/output functions for new data types.\u003c/p\u003e\n\u003cp\u003eSometimes it is desirable to write Tcl functions that are not restricted to safe Tcl. For example, one might want a Tcl function that sends email. To handle these cases, there is a variant of \u003cspan\u003ePL/Tcl\u003c/span\u003e called \u003ccode\u003ePL/TclU\u003c/code\u003e (for untrusted Tcl). This is exactly the same language except that a full Tcl interpreter is used. \u003cspan\u003e\u003cem\u003eIf \u003cspan\u003ePL/TclU\u003c/span\u003e is used, it must be installed as an untrusted procedural language\u003c/em\u003e\u003c/span\u003e so that only database superusers can create functions in it. The writer of a \u003cspan\u003ePL/TclU\u003c/span\u003e function must take care that the function cannot be used to do anything unwanted, since it will be able to do anything that could be done by a user logged in as the database administrator.\u003c/p\u003e\n\u003cp\u003eThe shared object code for the \u003cspan\u003ePL/Tcl\u003c/span\u003e and \u003cspan\u003ePL/TclU\u003c/span\u003e call handlers is automatically built and installed in the \u003cspan\u003ePostgreSQL\u003c/span\u003e library directory if Tcl support is specified in the configuration step of the installation procedure. 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