| '\" |
| '\" Copyright (c) 1993 The Regents of the University of California. |
| '\" Copyright (c) 1994-1996 Sun Microsystems, Inc. |
| '\" Copyright (c) 2000 Ajuba Solutions. |
| '\" |
| '\" See the file "license.terms" for information on usage and redistribution |
| '\" of this file, and for a DISCLAIMER OF ALL WARRANTIES. |
| '\" |
| '\" RCS: @(#) $Id: trace.n,v 1.11 2002/07/16 22:27:35 dgp Exp $ |
| '\" |
| '\" The definitions below are for supplemental macros used in Tcl/Tk |
| '\" manual entries. |
| '\" |
| '\" .AP type name in/out ?indent? |
| '\" Start paragraph describing an argument to a library procedure. |
| '\" type is type of argument (int, etc.), in/out is either "in", "out", |
| '\" or "in/out" to describe whether procedure reads or modifies arg, |
| '\" and indent is equivalent to second arg of .IP (shouldn't ever be |
| '\" needed; use .AS below instead) |
| '\" |
| '\" .AS ?type? ?name? |
| '\" Give maximum sizes of arguments for setting tab stops. Type and |
| '\" name are examples of largest possible arguments that will be passed |
| '\" to .AP later. If args are omitted, default tab stops are used. |
| '\" |
| '\" .BS |
| '\" Start box enclosure. From here until next .BE, everything will be |
| '\" enclosed in one large box. |
| '\" |
| '\" .BE |
| '\" End of box enclosure. |
| '\" |
| '\" .CS |
| '\" Begin code excerpt. |
| '\" |
| '\" .CE |
| '\" End code excerpt. |
| '\" |
| '\" .VS ?version? ?br? |
| '\" Begin vertical sidebar, for use in marking newly-changed parts |
| '\" of man pages. The first argument is ignored and used for recording |
| '\" the version when the .VS was added, so that the sidebars can be |
| '\" found and removed when they reach a certain age. If another argument |
| '\" is present, then a line break is forced before starting the sidebar. |
| '\" |
| '\" .VE |
| '\" End of vertical sidebar. |
| '\" |
| '\" .DS |
| '\" Begin an indented unfilled display. |
| '\" |
| '\" .DE |
| '\" End of indented unfilled display. |
| '\" |
| '\" .SO |
| '\" Start of list of standard options for a Tk widget. The |
| '\" options follow on successive lines, in four columns separated |
| '\" by tabs. |
| '\" |
| '\" .SE |
| '\" End of list of standard options for a Tk widget. |
| '\" |
| '\" .OP cmdName dbName dbClass |
| '\" Start of description of a specific option. cmdName gives the |
| '\" option's name as specified in the class command, dbName gives |
| '\" the option's name in the option database, and dbClass gives |
| '\" the option's class in the option database. |
| '\" |
| '\" .UL arg1 arg2 |
| '\" Print arg1 underlined, then print arg2 normally. |
| '\" |
| '\" RCS: @(#) $Id: man.macros,v 1.4 2000/08/25 06:18:32 ericm Exp $ |
| '\" |
| '\" # Set up traps and other miscellaneous stuff for Tcl/Tk man pages. |
| .if t .wh -1.3i ^B |
| .nr ^l \n(.l |
| .ad b |
| '\" # Start an argument description |
| .de AP |
| .ie !"\\$4"" .TP \\$4 |
| .el \{\ |
| . ie !"\\$2"" .TP \\n()Cu |
| . el .TP 15 |
| .\} |
| .ta \\n()Au \\n()Bu |
| .ie !"\\$3"" \{\ |
| \&\\$1 \\fI\\$2\\fP (\\$3) |
| .\".b |
| .\} |
| .el \{\ |
| .br |
| .ie !"\\$2"" \{\ |
| \&\\$1 \\fI\\$2\\fP |
| .\} |
| .el \{\ |
| \&\\fI\\$1\\fP |
| .\} |
| .\} |
| .. |
| '\" # define tabbing values for .AP |
| .de AS |
| .nr )A 10n |
| .if !"\\$1"" .nr )A \\w'\\$1'u+3n |
| .nr )B \\n()Au+15n |
| .\" |
| .if !"\\$2"" .nr )B \\w'\\$2'u+\\n()Au+3n |
| .nr )C \\n()Bu+\\w'(in/out)'u+2n |
| .. |
| .AS Tcl_Interp Tcl_CreateInterp in/out |
| '\" # BS - start boxed text |
| '\" # ^y = starting y location |
| '\" # ^b = 1 |
| .de BS |
| .br |
| .mk ^y |
| .nr ^b 1u |
| .if n .nf |
| .if n .ti 0 |
| .if n \l'\\n(.lu\(ul' |
| .if n .fi |
| .. |
| '\" # BE - end boxed text (draw box now) |
| .de BE |
| .nf |
| .ti 0 |
| .mk ^t |
| .ie n \l'\\n(^lu\(ul' |
| .el \{\ |
| .\" Draw four-sided box normally, but don't draw top of |
| .\" box if the box started on an earlier page. |
| .ie !\\n(^b-1 \{\ |
| \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' |
| .\} |
| .el \}\ |
| \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\l'|0u-1.5n\(ul' |
| .\} |
| .\} |
| .fi |
| .br |
| .nr ^b 0 |
| .. |
| '\" # VS - start vertical sidebar |
| '\" # ^Y = starting y location |
| '\" # ^v = 1 (for troff; for nroff this doesn't matter) |
| .de VS |
| .if !"\\$2"" .br |
| .mk ^Y |
| .ie n 'mc \s12\(br\s0 |
| .el .nr ^v 1u |
| .. |
| '\" # VE - end of vertical sidebar |
| .de VE |
| .ie n 'mc |
| .el \{\ |
| .ev 2 |
| .nf |
| .ti 0 |
| .mk ^t |
| \h'|\\n(^lu+3n'\L'|\\n(^Yu-1v\(bv'\v'\\n(^tu+1v-\\n(^Yu'\h'-|\\n(^lu+3n' |
| .sp -1 |
| .fi |
| .ev |
| .\} |
| .nr ^v 0 |
| .. |
| '\" # Special macro to handle page bottom: finish off current |
| '\" # box/sidebar if in box/sidebar mode, then invoked standard |
| '\" # page bottom macro. |
| .de ^B |
| .ev 2 |
| 'ti 0 |
| 'nf |
| .mk ^t |
| .if \\n(^b \{\ |
| .\" Draw three-sided box if this is the box's first page, |
| .\" draw two sides but no top otherwise. |
| .ie !\\n(^b-1 \h'-1.5n'\L'|\\n(^yu-1v'\l'\\n(^lu+3n\(ul'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c |
| .el \h'-1.5n'\L'|\\n(^yu-1v'\h'\\n(^lu+3n'\L'\\n(^tu+1v-\\n(^yu'\h'|0u'\c |
| .\} |
| .if \\n(^v \{\ |
| .nr ^x \\n(^tu+1v-\\n(^Yu |
| \kx\h'-\\nxu'\h'|\\n(^lu+3n'\ky\L'-\\n(^xu'\v'\\n(^xu'\h'|0u'\c |
| .\} |
| .bp |
| 'fi |
| .ev |
| .if \\n(^b \{\ |
| .mk ^y |
| .nr ^b 2 |
| .\} |
| .if \\n(^v \{\ |
| .mk ^Y |
| .\} |
| .. |
| '\" # DS - begin display |
| .de DS |
| .RS |
| .nf |
| .sp |
| .. |
| '\" # DE - end display |
| .de DE |
| .fi |
| .RE |
| .sp |
| .. |
| '\" # SO - start of list of standard options |
| .de SO |
| .SH "STANDARD OPTIONS" |
| .LP |
| .nf |
| .ta 5.5c 11c |
| .ft B |
| .. |
| '\" # SE - end of list of standard options |
| .de SE |
| .fi |
| .ft R |
| .LP |
| See the \\fBoptions\\fR manual entry for details on the standard options. |
| .. |
| '\" # OP - start of full description for a single option |
| .de OP |
| .LP |
| .nf |
| .ta 4c |
| Command-Line Name: \\fB\\$1\\fR |
| Database Name: \\fB\\$2\\fR |
| Database Class: \\fB\\$3\\fR |
| .fi |
| .IP |
| .. |
| '\" # CS - begin code excerpt |
| .de CS |
| .RS |
| .nf |
| .ta .25i .5i .75i 1i |
| .. |
| '\" # CE - end code excerpt |
| .de CE |
| .fi |
| .RE |
| .. |
| .de UL |
| \\$1\l'|0\(ul'\\$2 |
| .. |
| .TH trace n "8.4" Tcl "Tcl Built-In Commands" |
| .BS |
| '\" Note: do not modify the .SH NAME line immediately below! |
| .SH NAME |
| trace \- Monitor variable accesses, command usages and command executions |
| .SH SYNOPSIS |
| \fBtrace \fIoption\fR ?\fIarg arg ...\fR? |
| .BE |
| |
| .SH DESCRIPTION |
| .PP |
| This command causes Tcl commands to be executed whenever certain operations are |
| invoked. The legal \fIoption\fR's (which may be abbreviated) are: |
| .TP |
| \fBtrace add \fItype name ops ?args?\fR |
| Where \fItype\fR is \fBcommand\fR, \fBexecution\fR, or \fBvariable\fR. |
| .RS |
| .TP |
| \fBtrace add command\fR \fIname ops command\fR |
| Arrange for \fIcommand\fR to be executed whenever command \fIname\fR |
| is modified in one of the ways given by the list \fIops\fR. \fIName\fR will be |
| resolved using the usual namespace resolution rules used by |
| procedures. If the command does not exist, an error will be thrown. |
| .RS |
| .PP |
| \fIOps\fR indicates which operations are of interest, and is a list of |
| one or more of the following items: |
| .TP |
| \fBrename\fR |
| Invoke \fIcommand\fR whenever the command is renamed. Note that |
| renaming to the empty string is considered deletion, and will not |
| be traced with '\fBrename\fR'. |
| .TP |
| \fBdelete\fR |
| Invoke \fIcommand\fR when the command is deleted. Commands can be |
| deleted explicitly by using the \fBrename\fR command to rename the |
| command to an empty string. Commands are also deleted when the |
| interpreter is deleted, but traces will not be invoked because there is no |
| interpreter in which to execute them. |
| .PP |
| When the trace triggers, depending on the operations being traced, a |
| number of arguments are appended to \fIcommand\fR so that the actual |
| command is as follows: |
| .CS |
| \fIcommand oldName newName op\fR |
| .CE |
| \fIOldName\fR and \fInewName\fR give the traced command's current |
| (old) name, and the name to which it is being renamed (the empty |
| string if this is a 'delete' operation). |
| \fIOp\fR indicates what operation is being performed on the |
| command, and is one of \fBrename\fR or \fBdelete\fR as |
| defined above. The trace operation cannot be used to stop a command |
| from being deleted. Tcl will always remove the command once the trace |
| is complete. Recursive renaming or deleting will not cause further traces |
| of the same type to be evaluated, so a delete trace which itself |
| deletes the command, or a rename trace which itself renames the |
| command will not cause further trace evaluations to occur. |
| .RE |
| .TP |
| \fBtrace add execution\fR \fIname ops command\fR |
| Arrange for \fIcommand\fR to be executed whenever command \fIname\fR |
| is modified in one of the ways given by the list \fIops\fR. \fIName\fR will be |
| resolved using the usual namespace resolution rules used by |
| procedures. If the command does not exist, an error will be thrown. |
| .RS |
| .PP |
| \fIOps\fR indicates which operations are of interest, and is a list of |
| one or more of the following items: |
| .TP |
| \fBenter\fR |
| Invoke \fIcommand\fR whenever the command \fIname\fR is executed, |
| just before the actual execution takes place. |
| .TP |
| \fBleave\fR |
| Invoke \fIcommand\fR whenever the command \fIname\fR is executed, |
| just after the actual execution takes place. |
| .TP |
| \fBenterstep\fR |
| Invoke \fIcommand\fR for every tcl command which is executed |
| inside the procedure \fIname\fR, just before the actual execution |
| takes place. For example if we have 'proc foo {} { puts "hello" }', |
| then a \fIenterstep\fR trace would be |
| invoked just before \fIputs "hello"\fR is executed. |
| Setting a \fIenterstep\fR trace on a \fIcommand\fR |
| will not result in an error and is simply ignored. |
| .TP |
| \fBleavestep\fR |
| Invoke \fIcommand\fR for every tcl command which is executed |
| inside the procedure \fIname\fR, just after the actual execution |
| takes place. |
| Setting a \fIleavestep\fR trace on a \fIcommand\fR |
| will not result in an error and is simply ignored. |
| .PP |
| When the trace triggers, depending on the operations being traced, a |
| number of arguments are appended to \fIcommand\fR so that the actual |
| command is as follows: |
| |
| For \fBenter\fR and \fBenterstep\fR operations: |
| .CS |
| \fIcommand command-string op\fR |
| .CE |
| \fICommand-string\fR gives the complete current command being |
| executed (the traced command for a \fBenter\fR operation, an |
| arbitrary command for a \fBenterstep\fR operation), including |
| all arguments in their fully expanded form. |
| \fIOp\fR indicates what operation is being performed on the |
| command execution, and is one of \fBenter\fR or \fBenterstep\fR as |
| defined above. The trace operation can be used to stop the |
| command from executing, by deleting the command in question. Of |
| course when the command is subsequently executed, an 'invalid command' |
| error will occur. |
| .TP |
| For \fBleave\fR and \fBleavestep\fR operations: |
| .CS |
| \fIcommand command-string code result op\fR |
| .CE |
| \fICommand-string\fR gives the complete current command being |
| executed (the traced command for a \fBenter\fR operation, an |
| arbitrary command for a \fBenterstep\fR operation), including |
| all arguments in their fully expanded form. |
| \fICode\fR gives the result code of that execution, and \fIresult\fR |
| the result string. |
| \fIOp\fR indicates what operation is being performed on the |
| command execution, and is one of \fBleave\fR or \fBleavestep\fR as |
| defined above. |
| Note that the creation of many \fBenterstep\fR or |
| \fBleavestep\fR traces can lead to unintuitive results, since the |
| invoked commands from one trace can themselves lead to further |
| command invocations for other traces. |
| |
| \fICommand\fR executes in the same context as the code that invoked |
| the traced operation: thus the \fIcommand\fR, if invoked from a procedure, |
| will have access to the same local variables as code in the procedure. |
| This context may be different than the context in which the trace was |
| created. If \fIcommand\fR invokes a procedure (which it normally does) |
| then the procedure will have to use upvar or uplevel commands if it wishes |
| to access the local variables of the code which invoked the trace operation. |
| |
| While \fIcommand\fR is executing during an execution trace, traces |
| on \fIname\fR are temporarily disabled. This allows the \fIcommand\fR |
| to execute \fIname\fR in its body without invoking any other traces again. |
| If an error occurs while executing the \fIcommand\fR body, then the |
| \fIcommand\fR name as a whole will return that same error. |
| |
| When multiple traces are set on \fIname\fR, then for \fIenter\fR |
| and \fIenterstep\fR operations, the traced commands are invoked |
| in the reverse order of how the traces were originally created; |
| and for \fIleave\fR and \fIleavestep\fR operations, the traced |
| commands are invoked in the original order of creation. |
| |
| The behavior of execution traces is currently undefined for a command |
| \fIname\fR imported into another namespace. |
| .RE |
| .TP |
| \fBtrace add variable\fI name ops command\fR |
| Arrange for \fIcommand\fR to be executed whenever variable \fIname\fR |
| is accessed in one of the ways given by the list \fIops\fR. \fIName\fR may |
| refer to a normal variable, an element of an array, or to an array |
| as a whole (i.e. \fIname\fR may be just the name of an array, with no |
| parenthesized index). If \fIname\fR refers to a whole array, then |
| \fIcommand\fR is invoked whenever any element of the array is |
| manipulated. If the variable does not exist, it will be created but |
| will not be given a value, so it will be visible to \fBnamespace which\fR |
| queries, but not to \fBinfo exists\fR queries. |
| .RS |
| .PP |
| \fIOps\fR indicates which operations are of interest, and is a list of |
| one or more of the following items: |
| .TP |
| \fBarray\fR |
| Invoke \fIcommand\fR whenever the variable is accessed or modified via |
| the \fBarray\fR command, provided that \fIname\fR is not a scalar |
| variable at the time that the \fBarray\fR command is invoked. If |
| \fIname\fR is a scalar variable, the access via the \fBarray\fR |
| command will not trigger the trace. |
| .TP |
| \fBread\fR |
| Invoke \fIcommand\fR whenever the variable is read. |
| .TP |
| \fBwrite\fR |
| Invoke \fIcommand\fR whenever the variable is written. |
| .TP |
| \fBunset\fR |
| Invoke \fIcommand\fR whenever the variable is unset. Variables |
| can be unset explicitly with the \fBunset\fR command, or |
| implicitly when procedures return (all of their local variables |
| are unset). Variables are also unset when interpreters are |
| deleted, but traces will not be invoked because there is no |
| interpreter in which to execute them. |
| .PP |
| When the trace triggers, three arguments are appended to |
| \fIcommand\fR so that the actual command is as follows: |
| .CS |
| \fIcommand name1 name2 op\fR |
| .CE |
| \fIName1\fR and \fIname2\fR give the name(s) for the variable |
| being accessed: if the variable is a scalar then \fIname1\fR |
| gives the variable's name and \fIname2\fR is an empty string; |
| if the variable is an array element then \fIname1\fR gives the |
| name of the array and name2 gives the index into the array; |
| if an entire array is being deleted and the trace was registered |
| on the overall array, rather than a single element, then \fIname1\fR |
| gives the array name and \fIname2\fR is an empty string. |
| \fIName1\fR and \fIname2\fR are not necessarily the same as the |
| name used in the \fBtrace variable\fR command: the \fBupvar\fR |
| command allows a procedure to reference a variable under a |
| different name. |
| \fIOp\fR indicates what operation is being performed on the |
| variable, and is one of \fBread\fR, \fBwrite\fR, or \fBunset\fR as |
| defined above. |
| .PP |
| \fICommand\fR executes in the same context as the code that invoked |
| the traced operation: if the variable was accessed as part of a Tcl |
| procedure, then \fIcommand\fR will have access to the same local |
| variables as code in the procedure. This context may be different |
| than the context in which the trace was created. If \fIcommand\fR |
| invokes a procedure (which it normally does) then the procedure will |
| have to use \fBupvar\fR or \fBuplevel\fR if it wishes to access the |
| traced variable. Note also that \fIname1\fR may not necessarily be |
| the same as the name used to set the trace on the variable; |
| differences can occur if the access is made through a variable defined |
| with the \fBupvar\fR command. |
| .PP |
| For read and write traces, \fIcommand\fR can modify the variable to |
| affect the result of the traced operation. If \fIcommand\fR modifies |
| the value of a variable during a read or write trace, then the new |
| value will be returned as the result of the traced operation. The |
| return value from \fIcommand\fR is ignored except that if it returns |
| an error of any sort then the traced operation also returns an error |
| with the same error message returned by the trace command (this |
| mechanism can be used to implement read-only variables, for example). |
| For write traces, \fIcommand\fR is invoked after the variable's value |
| has been changed; it can write a new value into the variable to |
| override the original value specified in the write operation. To |
| implement read-only variables, \fIcommand\fR will have to restore the |
| old value of the variable. |
| .PP |
| While \fIcommand\fR is executing during a read or write trace, traces |
| on the variable are temporarily disabled. This means that reads and |
| writes invoked by \fIcommand\fR will occur directly, without invoking |
| \fIcommand\fR (or any other traces) again. However, if \fIcommand\fR |
| unsets the variable then unset traces will be invoked. |
| .PP |
| When an unset trace is invoked, the variable has already been deleted: |
| it will appear to be undefined with no traces. If an unset occurs |
| because of a procedure return, then the trace will be invoked in the |
| variable context of the procedure being returned to: the stack frame |
| of the returning procedure will no longer exist. Traces are not |
| disabled during unset traces, so if an unset trace command creates a |
| new trace and accesses the variable, the trace will be invoked. Any |
| errors in unset traces are ignored. |
| .PP |
| If there are multiple traces on a variable they are invoked in order |
| of creation, most-recent first. If one trace returns an error, then |
| no further traces are invoked for the variable. If an array element |
| has a trace set, and there is also a trace set on the array as a |
| whole, the trace on the overall array is invoked before the one on the |
| element. |
| .PP |
| Once created, the trace remains in effect either until the trace is |
| removed with the \fBtrace remove variable\fR command described below, |
| until the variable is unset, or until the interpreter is deleted. |
| Unsetting an element of array will remove any traces on that element, |
| but will not remove traces on the overall array. |
| .PP |
| This command returns an empty string. |
| .RE |
| .RE |
| .TP |
| \fBtrace remove \fItype name opList command\fR |
| Where \fItype\fR is either \fBcommand\fR, \fBexecution\fR or \fBvariable\fR. |
| .RS |
| .TP |
| \fBtrace remove command\fI name opList command\fR |
| If there is a trace set on command \fIname\fR with the operations and |
| command given by \fIopList\fR and \fIcommand\fR, then the trace is |
| removed, so that \fIcommand\fR will never again be invoked. Returns |
| an empty string. If \fIname\fR doesn't exist, the command will throw |
| an error. |
| .TP |
| \fBtrace remove execution\fI name opList command\fR |
| If there is a trace set on command \fIname\fR with the operations and |
| command given by \fIopList\fR and \fIcommand\fR, then the trace is |
| removed, so that \fIcommand\fR will never again be invoked. Returns |
| an empty string. If \fIname\fR doesn't exist, the command will throw |
| an error. |
| .TP |
| \fBtrace remove variable\fI name opList command\fR |
| If there is a trace set on variable \fIname\fR with the operations and |
| command given by \fIopList\fR and \fIcommand\fR, then the trace is |
| removed, so that \fIcommand\fR will never again be invoked. Returns |
| an empty string. |
| .RE |
| .TP |
| \fBtrace info \fItype name\fR |
| Where \fItype\fR is either \fBcommand\fR, \fBexecution\fR or \fBvariable\fR. |
| .RS |
| .TP |
| \fBtrace info command\fI name\fR |
| Returns a list containing one element for each trace currently set on |
| command \fIname\fR. Each element of the list is itself a list |
| containing two elements, which are the \fIopList\fR and \fIcommand\fR |
| associated with the trace. If \fIname\fR doesn't have any traces set, |
| then the result of the command will be an empty string. If \fIname\fR |
| doesn't exist, the command will throw an error. |
| .TP |
| \fBtrace info execution\fI name\fR |
| Returns a list containing one element for each trace currently set on |
| command \fIname\fR. Each element of the list is itself a list |
| containing two elements, which are the \fIopList\fR and \fIcommand\fR |
| associated with the trace. If \fIname\fR doesn't have any traces set, |
| then the result of the command will be an empty string. If \fIname\fR |
| doesn't exist, the command will throw an error. |
| .TP |
| \fBtrace info variable\fI name\fR |
| Returns a list containing one element for each trace currently set on |
| variable \fIname\fR. Each element of the list is itself a list |
| containing two elements, which are the \fIopList\fR and \fIcommand\fR |
| associated with the trace. If \fIname\fR doesn't exist or doesn't |
| have any traces set, then the result of the command will be an empty |
| string. |
| .RE |
| .PP |
| For backwards compatibility, three other subcommands are available: |
| .RS |
| .TP |
| \fBtrace variable \fIname ops command\fR |
| This is equivalent to \fBtrace add variable \fIname ops command\fR. |
| .TP |
| \fBtrace vdelete \fIname ops command\fR |
| This is equivalent to \fBtrace remove variable \fIname ops command\fR |
| .TP |
| \fBtrace vinfo \fIname\fR |
| This is equivalent to \fBtrace info variable \fIname\fR |
| .RE |
| .PP |
| These subcommands are deprecated and will likely be removed in a |
| future version of Tcl. They use an older syntax in which \fBarray\fR, |
| \fBread\fR, \fBwrite\fR, \fBunset\fR are replaced by \fBa\fR, \fBr\fR, |
| \fBw\fR and \fBu\fR respectively, and the \fIops\fR argument is not a |
| list, but simply a string concatenation of the operations, such as |
| \fBrwua\fR. |
| |
| .SH "SEE ALSO" |
| set(n), unset(n) |
| |
| .SH KEYWORDS |
| read, command, rename, variable, write, trace, unset |