TCL - 读取文件，额外行

Question

I have written the script below, and for some reason it output an extra 3rd line (top out.txt & name ). How do I stop it from outputing the last 2 line to the output file.

I think is because of this line but not too sure: set lines [split [read $list] "\n"]

Input put file - a.txt
**********************
abc
bcd

Output
*******
top out.txt 
name abc 
top out.txt 
name bcd 
top out.txt 
name 

set outfile      [open "out.txt" w]
set list         [open "a.list" r]
set dir         "[glob a.txt]"

    foreach ddd $dir {
        set lines [split [read $list] "\n"]
        foreach line $lines {
                puts $outfile "top $dir"
                puts $outfile "name $line"
        }
    }
close $list
close $outfile

Answer 1

The core of the issue is that split works with field separators and not field terminators; this is where you see the difference between the two.

If we look at the characters of your file, we'll see this: a b c \n b c d \n . (Technically, the \n might instead be \r \n or \r ; Tcl auto-adapts to that by default for text files.) If we split those characters at the \n , we get these substrings: abc , bcd , and the empty string for the characters after that final \n . This means that when we join the strings with \n (as the joiner string) between all the elements, we get the original string back again.

---

You've got a few options for dealing with this. My favourite is to add code to ignore blank lines; versions of this are particularly useful for all sorts of human-written lists (as it's fairly easy to also add in comment skipping):

    set lines [split [read $list] "\n"]
    foreach line $lines {
        if {$line eq ""} continue
        puts $outfile "top $dir"
        puts $outfile "name $line"
    }

Another option is to use the -nonewline option to read to discard that final \n :

    set lines [split [read -nonewline $list] "\n"]
    foreach line $lines {
        puts $outfile "top $dir"
        puts $outfile "name $line"
    }

You could also string trimright before splitting, but that would strip multiple newlines from the end (if they're present).

    set lines [split [string trimright [read $list] "\n"] "\n"]
    foreach line $lines {
        puts $outfile "top $dir"
        puts $outfile "name $line"
    }

Finally, if you're using a machine-generated list, you could consider just getting that code to not put a newline at the end. Sometimes that's the easiest option of all.