subst command is useful.
Subst performs a substitution pass without performing any
execution of commands except those required for the substitution to
occur, ie: commands within [] will be executed, and the results
placed in the return string.
In the example code:
puts "[subst $$c]\n"shows an example of placing a variable name in a variable, and evaluating through the indirection.
The format command can also be used to force some levels of
substitution to occur.
subst ?-nobackslashes? ?-nocommands? ?-novariables? stringstring through the Tcl substitution phase, and returns the
original string with the
backslash sequences, commands and variables replaced by their equivalents.
If any of the -no... arguments are present, then that set of
substitutions will not be done.
NOTE: subst does not honor braces or quotes.
set a "alpha"
set b a
puts {a and b with no substitution: $a $$b}
puts "a and b with one pass of substitution: $a $$b"
puts "a and b with subst in braces: [subst {$a $$b}]"
puts "a and b with subst in quotes: [subst "$a $$b"]\n"
puts "format with no subst [format {$%s} $b]"
puts "format with subst: [subst [format {$%s} $b]]"
eval "puts \"eval after format: [format {$%s} $b]\""
set num 0;
set cmd "proc tempFileName {} "
set cmd [format "%s {global num; incr num;" $cmd]
set cmd [format {%s return "/tmp/TMP.%s.$num"} $cmd [pid] ]
set cmd [format "%s }" $cmd ]
eval $cmd
puts "[info body tempFileName]"
set a arrayname
set b index
set c newvalue
eval [format "set %s(%s) %s" $a $b $c]
puts "Index: $b of $a was set to: $arrayname(index)"