Scroll to navigation

subst(3tcl) Tcl Built-In Commands subst(3tcl) 





NAME


subst - Perform backslash, command, and variable substitutions






SYNOPSIS


subst ?-nobackslashes? ?-nocommands?
    ?-novariables? string










DESCRIPTION


This command performs variable substitutions, command
    substitutions, and backslash substitutions on its string argument and
    returns the fully-substituted result. The substitutions are performed in
    exactly the same way as for Tcl commands. As a result, the string
    argument is actually substituted twice, once by the Tcl parser in the usual
    fashion for Tcl commands, and again by the subst command.


If any of the -nobackslashes, -nocommands, or
    -novariables are specified, then the corresponding substitutions are
    not performed. For example, if -nocommands is specified, command
    substitution is not performed: open and close brackets are treated as
    ordinary characters with no special interpretation.


Note that the substitution of one kind can include substitution of
    other kinds. For example, even when the -novariables option is
    specified, command substitution is performed without restriction. This means
    that any variable substitution necessary to complete the command
    substitution will still take place. Likewise, any command substitution
    necessary to complete a variable substitution will take place, even when
    -nocommands is specified. See the EXAMPLES below.


If an error occurs during substitution, then subst will
    return that error. If a break exception occurs during command or variable
    substitution, the result of the whole substitution will be the string (as
    substituted) up to the start of the substitution that raised the exception.
    If a continue exception occurs during the evaluation of a command or
    variable substitution, an empty string will be substituted for that entire
    command or variable substitution (as long as it is well-formed Tcl.) If a
    return exception occurs, or any other return code is returned during command
    or variable substitution, then the returned value is substituted for that
    substitution. See the EXAMPLES below. In this way, all exceptional return
    codes are ``caught'' by subst. The subst command itself will
    either return an error, or will complete successfully.






EXAMPLES


When it performs its substitutions, subst does not give any
    special treatment to double quotes or curly braces (except within command
    substitutions) so the script




set a 44
subst {xyz {$a}}



returns ``xyz {44}'', not ``xyz {$a}'' and the script



set a "p\} q \{r"
subst {xyz {$a}}



return ``xyz {p} q {r}'', not ``xyz {p\} q \{r}''.

When command substitution is performed, it includes any variable
    substitution necessary to evaluate the script.




set a 44
subst -novariables {$a [format $a]}



returns ``$a 44'', not ``$a $a''. Similarly, when variable
  substitution is performed, it includes any command substitution necessary to
  retrieve the value of the variable.



proc b {} {return c}
array set a {c c [b] tricky}
subst -nocommands {[b] $a([b])}



returns ``[b] c'', not ``[b] tricky''.

The continue and break exceptions allow command substitutions to
    prevent substitution of the rest of the command substitution and the rest of
    string respectively, giving script authors more options when
    processing text using subst. For example, the script




subst {abc,[break],def}



returns ``abc,'', not ``abc,,def'' and the script



subst {abc,[continue;expr 1+2],def}



returns ``abc,,def'', not ``abc,3,def''.

Other exceptional return codes substitute the returned value




subst {abc,[return foo;expr 1+2],def}



returns ``abc,foo,def'', not ``abc,3,def'' and



subst {abc,[return -code 10 foo;expr 1+2],def}



also returns ``abc,foo,def'', not ``abc,3,def''.







SEE ALSO


Tcl(3tcl), eval(3tcl), break(3tcl), continue(3tcl)








KEYWORDS


backslash substitution, command substitution, variable
    substitution







  

    7.4
    Tcl