TCL - More command construction - format, list

There may be some unexpected results when you try to compose command strings for eval.

For instance

eval puts OK

would print the string OK. However,

eval puts Not OK

will generate an error.

The reason that the second command generates an error is that the eval uses concat to merge its arguments into a command string. This causes the two words Not OK to be treated as two arguments to puts. If there is more than one argument to puts, the first argument must be a file pointer.

Correct ways to write the second command include these:

eval [list puts {Not OK}]
eval [list puts "Not OK"]

md {Not OK}; eval $cmd

set cmd "puts" ; lappend 
c

As long as you keep track of how the arguments you present to eval will be grouped, you can use many methods of creating the strings for eval, including the string commands and format.

The recommended methods of constructing commands for eval is to use the list and lappend commands. These commands become difficult to use, however if you need to put braces in the command, as was done in the previous lesson.

The example from the previous lesson is re-implemented in the example code using lappend.

The completeness of a command can be checked with info complete. Info complete can also be used in an interactive program to determine if the line being typed in is a complete command, or the user just entered a newline to format the command better.

info complete string

If string has no unmatched brackets, braces or parentheses, then a value of 1 is returned, else 0 is returned.

---

Example

set cmd "OK"

eval puts $cmd

et cmd "puts" ; lappend cmd {Also OK}; eval $cmd

s
set cmd "NOT OK"
eval puts $cmd


his Works"]

set cmd "And even this can be mad
eval [format {%s "%s"} puts "Even 
Te to work"

eval [format {%s "%s"} puts $cmd ]

set tmpFileNum 0;


m; incr num; return \"/tmp/T
set cmd {proc tempFileName }
lappend cmd ""  
lappend cmd "global n
uMP.[pid].\$num\""
eval  $cmd

puts "\nThis is the body of the proc definition:"

ete $cmd]} {
    eval $cmd
} else
puts "[info body tempFileName]\n"

set cmd {puts "This is Cool!}

if {[info comp
l {
    puts "INCOMPLETE COMMAND: $cmd"


}