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'\"
'\" Copyright (c) 2001 Donal K. Fellows
'\"
'\" See the file "license.terms" for information on usage and redistribution
'\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
'\"
.TH Tcl_SubstObj 3 8.4 Tcl "Tcl Library Procedures"
.so man.macros
.BS
.SH NAME
Tcl_SubstObj \- perform substitutions on Tcl values
.SH SYNOPSIS
.nf
\fB#include <tcl.h>\fR
.sp
Tcl_Obj *
\fBTcl_SubstObj\fR(\fIinterp, objPtr, flags\fR)
.SH ARGUMENTS
.AS Tcl_Interp **termPtr
.AP Tcl_Interp *interp in
Interpreter in which to execute Tcl scripts and lookup variables. If
an error occurs, the interpreter's result is modified to hold an error
message.
.AP Tcl_Obj *objPtr in
A Tcl value containing the string to perform substitutions on.
.AP int flags in
ORed combination of flag bits that specify which substitutions to
perform. The flags \fBTCL_SUBST_COMMANDS\fR,
\fBTCL_SUBST_VARIABLES\fR and \fBTCL_SUBST_BACKSLASHES\fR are
currently supported, and \fBTCL_SUBST_ALL\fR is provided as a
convenience for the common case where all substitutions are desired.
.BE
.SH DESCRIPTION
.PP
The \fBTcl_SubstObj\fR function is used to perform substitutions on
strings in the fashion of the \fBsubst\fR command. It gets the value
of the string contained in \fIobjPtr\fR and scans it, copying
characters and performing the chosen substitutions as it goes to an
output value which is returned as the result of the function. In the
event of an error occurring during the execution of a command or
variable substitution, the function returns NULL and an error message
is left in \fIinterp\fR's result.
.PP
Three kinds of substitutions are supported. When the
\fBTCL_SUBST_BACKSLASHES\fR bit is set in \fIflags\fR, sequences that
look like backslash substitutions for Tcl commands are replaced by
their corresponding character.
.PP
When the \fBTCL_SUBST_VARIABLES\fR bit is set in \fIflags\fR,
sequences that look like variable substitutions for Tcl commands are
replaced by the contents of the named variable.
.PP
When the \fBTCL_SUBST_COMMANDS\fR bit is set in \fIflags\fR, sequences
that look like command substitutions for Tcl commands are replaced by
the result of evaluating that script. Where an uncaught
.QW "continue exception"
occurs during the evaluation of a command substitution, an
empty string is substituted for the command. Where an uncaught
.QW "break exception"
occurs during the evaluation of a command substitution, the
result of the whole substitution on \fIobjPtr\fR will be truncated at
the point immediately before the start of the command substitution,
and no characters will be added to the result or substitutions
performed after that point.
.SH "REFERENCE COUNT MANAGEMENT"
.PP
The \fIobjPtr\fR argument to \fBTcl_SubstObj\fR must not have a reference
count of zero. This function modifies the interpreter result, both on success
and on failure; the result of this function on success is exactly the current
interpreter result. Successful results should have their reference count
incremented if they are to be retained.
.SH "SEE ALSO"
subst(n)
.SH KEYWORDS
backslash substitution, command substitution, variable substitution
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