How to pass a tcl script a string and interpret it properly - tcl

Question

I'm trying to modify a tcl script that pushes bitfiles onto fpgas using xilinx's xsct tool. Here's what it looks like:
connect hw_server TCP:127.0.0.1:3122
targets -set -filter {jtag_cable_name =~ "Digilent JTAG-HS2 21xxx" && name =~ "xc7*"}
fpga [lindex $argv 0]
after 100
targets -set -filter {jtag_cable_name =~ "Digilent JTAG-HS2 21xxx" && name =~ "Micro*"}
loadhw system.hdf
stop
dow [lindex $argv 1]
con -block
Now that I have multiple FPGAs, I'd like to make the jtag_cable_name an argument. I've tried this to no avail:
connect hw_server TCP:127.0.0.1:3121
targets -set -filter {jtag_cable_name =~ [eval [lindex[$argv 0]] && name =~ "xc7*"}
fpga [lindex $argv 1]
after 100
targets -set -filter {jtag_cable_name =~ [eval [lindex[$argv 0]] && name =~ "Micro*"}
loadhw system.hdf
stop
dow [lindex $argv 2]
con -block
the call to the .tcl script looks like:
load_fpga.tcl "Digilent JTAG-HS2 21xxx" my_bitfile.bit my_elf.elf
How can I correctly pass the string and keep it in quotes like the original is?

Answer 1

What you don't realise is that in tcl, {Hello World} is a string.
If you are familiar with languages like Perl or Ruby than you would be familiar with the concept of literal and interpolated strings. In tcl, there are three syntaxes for strings:
Anything that doesn't contain a whitespace (space, tab, newline) is a string. Also, whitespace may be escaped. An escaped whitespace is not considered whitespace. The following are strings:
hello
hello\ world
Anything grouped by " are interpolated strings. Interpolated strings may contain variables or commands which will be evaluated and substituted. The following strings all say "hello world":
set x hello
"hello world"
"$x world"
"[set x] world"
Anything grouped by {} are literal strings. Literal strings aren't interpolated. That is, no variables or commands are evaluated. The following are literal strings:
{hello world} ;# hello world
{$x world} ;# $x world
There are two things you can do to get what you want
Replace {} with "". This will simply make the literal string into an interpolated string:
"jtag_cable_name =~ [eval [lindex[$argv 0]] && name =~ \"xc7*\""
note how you need to escape the " inside the string.
Use the subst command. The subst command performs substitutions on a string:
[subst {jtag_cable_name =~ [eval [lindex[$argv 0]] && name =~ "xc7*"}]
The small advantage of this is you don't need to escape the ". Read the manual page for subst. It's highly flexible allowing you to select what type of things you want to substitute. For example it allows you to evaluate only commands but not the $ syntax.

Answer 2

You probably want:
set jtag_cable_name [lindex $argv 0]
# ...
targets -set -filter [format {jtag_cable_name =~ "%s" && name =~ "xc7*"} $jtag_cable_name]
You can assign all the command line args like this:
lassign $argv jtag_cable_name bit_filename elf_filename