Tcl: variable not expanding from list given to foreach loop

Question

I was curious why the variable in my list doesn't expand when I perform a foreach loop...

set DIR_FILES "./files"

# HDL Library Files lists
set file_list {
   "$DIR_FILES/aa.txt" \
   "$DIR_FILES/bb.txt" \
   "$DIR_FILES/cc.txt" \
}

foreach library $file_list {
    puts ">>> ($library)";
}

Output is this:

>>> (./files/aa.txt)
>>> (./files/bb.txt)
>>> (./files/cc.txt)

Instead of this:

Output is this:

>>> ($DIR_FILES/aa.txt)
>>> ($DIR_FILES/bb.txt)
>>> ($DIR_FILES/cc.txt)

mrcalvin · Accepted Answer · 2020-05-19 06:57:15Z

2

I was curious why the variable in my list doesn't expand when I perform a foreach loop...

This is because the use of curly braces prevents variable substitution from happening (see Tcl doc):

Variable substitution is not performed on words enclosed in braces.

You might consider the following alternatives:

set file_list [list \
   $DIR_FILES/aa.txt \
   $DIR_FILES/bb.txt \
   $DIR_FILES/cc.txt
]

to create a Tcl list directly, rather than a string in list format.

or

set file_list [subst -nocommands -nobackslashes {
   $DIR_FILES/aa.txt
   $DIR_FILES/bb.txt
   $DIR_FILES/cc.txt
 }]

to spare the backslashes to cover for multi-line formatting.

answered May 19, 2020 at 6:57

mrcalvin

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1 Comment

Schelte Bron Over a year ago

Be cautious with the subst option. It has the same problem as enclosing the list in quotes when DIR_FILES contains a space. My advise would be to go for the solution that uses the list command.

Pico99 · Accepted Answer · 2020-05-18 19:45:42Z

-1

set DIR_FILES "./files"

# HDL Library Files lists
set file_list " \
   $DIR_FILES/aa.txt \
   $DIR_FILES/bb.txt \
   $DIR_FILES/cc.txt \
"

foreach library $file_list {
    puts ">>> ($library)";
}

answered May 18, 2020 at 19:45

Pico99

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2 Comments

Jeremy Caney Over a year ago

Because this is so close to the original code, it would be useful to provide an explanation of the difference—namely in terms of how you're closing the list. That will make it easier for the OP and future commentors to quickly parse what's going on. Can you edit your question to provide an explanation?

Schelte Bron Over a year ago

This will not produce the desired result if DIR_FILES contains a space. That's why it is usually better to use list commands to produce a list.

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