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Text File | 1994-09-20 | 9.7 KB | 265 lines

library(n) Tcl Built-In Commands _________________________________________________________________ NAME library - standard library of Tcl procedures SYNOPSIS auto_execok _c_m_d auto_load _c_m_d auto_mkindex _d_i_r _p_a_t_t_e_r_n _p_a_t_t_e_r_n ... auto_reset parray _a_r_r_a_y_N_a_m_e unknown _c_m_d ?_a_r_g _a_r_g ...? _________________________________________________________________ INTRODUCTION Tcl includes a library of Tcl procedures for commonly-needed functions. The procedures defined in the Tcl library are generic ones suitable for use by many different applica- tions. The location of the Tcl library is returned by the info library command. In addition to the Tcl library, each application will normally have its own library of support procedures as well; the location of this library is nor- mally given by the value of the $_a_p_p_library global vari- able, where _a_p_p is the name of the application. For exam- ple, the location of the Tk library is kept in the variable $tk_library. To access the procedures in the Tcl library, an application should source the file init.tcl in the library, for example with the Tcl command source [info library]/init.tcl This will define the unknown procedure and arrange for the other procedures to be loaded on-demand using the auto-load mechanism defined below. COMMAND PROCEDURES The following procedures are provided in the Tcl library: auto_execok _c_m_d Determines whether there is an executable file by the name _c_m_d. This command examines the directories in the current search path (given by the PATH enviornment variable) to see if there is an executable file named _c_m_d in any of those directories. If so, it returns 1; if not it returns 0. Auto_exec remembers information about previous searches in an array named auto_execs; this avoids the path search in future calls for the same _c_m_d. The command auto_reset may be used to force auto_execok to forget its cached information. Tcl 1 library(n) Tcl Built-In Commands auto_load _c_m_d This command attempts to load the definition for a Tcl command named _c_m_d. To do this, it searches an _a_u_t_o- _l_o_a_d _p_a_t_h, which is a list of one or more directories. The auto-load path is given by the global variable $auto_path if it exists. If there is no $auto_path variable, then the TCLLIBPATH environment variable is used, if it exists. Otherwise the auto-load path con- sists of just the Tcl library directory. Within each directory in the auto-load path there must be a file tclIndex that describes one or more commands defined in | that directory and a script to evaluate to load each of | the commands. The tclIndex file should be generated | with the auto_mkindex command. If _c_m_d is found in an | index file, then the appropriate script is evaluated to | create the command. The auto_load command returns 1 if _c_m_d was successfully created. The command returns 0 if there was no index entry for _c_m_d or if the script didn't actually define _c_m_d (e.g. because index informa- tion is out of date). If an error occurs while pro- cessing the script, then that error is returned. Auto_load only reads the index information once and saves it in the array auto_index; future calls to auto_load check for _c_m_d in the array rather than re- reading the index files. The cached index information may be deleted with the command auto_reset. This will force the next auto_load command to reload the index database from disk. auto_mkindex _d_i_r _p_a_t_t_e_r_n _p_a_t_t_e_r_n ... Generates an index suitable for use by auto_load. The | command searches _d_i_r for all files whose names match | any of the _p_a_t_t_e_r_n arguments (matching is done with the glob command), generates an index of all the Tcl com- mand procedures defined in all the matching files, and stores the index information in a file named tclIndex in _d_i_r. For example, the command auto_mkindex foo *.tcl will read all the .tcl files in subdirectory foo and generate a new index file foo/tclIndex. Auto_mkindex parses the Tcl scripts in a relatively unsophisticated way: if any line contains the word proc as its first characters then it is assumed to be a procedure definition and the next word of the line is taken as the procedure's name. Procedure definitions that don't appear in this way (e.g. they have spaces before the proc) will not be indexed. auto_reset Tcl 2 library(n) Tcl Built-In Commands Destroys all the information cached by auto_execok and auto_load. This information will be re-read from disk the next time it is needed. Auto_reset also deletes any procedures listed in the auto-load index, so that fresh copies of them will be loaded the next time that they're used. parray _a_r_r_a_y_N_a_m_e Prints on standard output the names and values of all the elements in the array _a_r_r_a_y_N_a_m_e. ArrayName must be an array accessible to the caller of parray. It may be either local or global. unknown _c_m_d ?_a_r_g _a_r_g ...? This procedure is invoked automatically by the Tcl interpreter whenever the name of a command doesn't exist. The unknown procedure receives as its arguments the name and arguments of the missing command. Unknown | first calls auto_load to load the command. If this succeeds, then it executes the original command with its original arguments. If the auto-load fails then unknown calls auto_execok to see if there is an execut- able file by the name _c_m_d. If so, it invokes the Tcl exec command with _c_m_d and all the _a_r_g_s as arguments. If _c_m_d can't be auto-executed, unknown checks to see if the command was invoked at top-level and outside of any script. If so, then unknown takes takes two additional steps. First, it sees if _c_m_d has one of the following three forms: !!, !_e_v_e_n_t, or ^_o_l_d^_n_e_w?^?. If so, then unknown carries out history substitution in the same way that csh would for these constructs. Second, and last, unknown checks to see if _c_m_d is a unique abbrevi- ation for an existing Tcl command. If so, it expands the command name and executes the command with the ori- ginal arguments. If none of the above efforts has been able to execute the command, unknown generates an error return. If the global variable auto_noload is defined, then the auto-load step is skipped. If the global variable auto_noexec is defined then the auto-exec step is skipped. Under normal circumstances the return value from unknown is the return value from the command that was eventually executed. VARIABLES The following global variables are defined or used by the procedures in the Tcl library: auto_execs Used by auto_execok to record information about whether particular commands exist as executable files. Tcl 3 library(n) Tcl Built-In Commands auto_index Used by auto_load to save the index information read from disk. auto_noexec If set to any value, then unknown will not attempt to auto-exec any commands. auto_noload If set to any value, then unknown will not attempt to auto-load any commands. auto_path If set, then it must contain a valid Tcl list giving directories to search during auto-load operations. env(TCL_LIBRARY) If set, then it specifies the location of the directory containing library scripts (the value of this variable will be returned by the command info library). If this variable isn't set then a default value is used. env(TCLLIBPATH) If set, then it must contain a valid Tcl list giving directories to search during auto-load operations. This variable is only used if auto_path is not defined. unknown_active This variable is set by unknown to indicate that it is active. It is used to detect errors where unknown recurses on itself infinitely. The variable is unset before unknown returns. KEYWORDS auto-exec, auto-load, library, unknown Tcl 4