Using eval exec with an executable name containing spaces in the path

Question

I came across this scenario, where I have to execute tshark for decoding the pcap file.

Location of of tshark is C:\\Program Files\\Wireshark\\tshark.exe

% set fileName TestTShark.pcap
TestTShark.pcap
% set sTsharkCmd "-r $fileName  -Tfields -e ip.src"
-r TestTShark.pcap  -Tfields -e ip.src
% set tsharkPath "C:/Program Files/Wireshark/tshark.exe"
C:/Program Files/Wireshark/tshark.exe
% eval exec $tsharkPath $sTsharkCmd > packet.log
couldn't execute "C:\Program": no such file or directory
% exec $tsharkPath $sTsharkCmd > packet.log
tshark: The file " TestTShark.pcap  -Tfields -e ip.src" doesn't exist.
% set tsharkPath "C:\\Program Files\\Wireshark\\tshark.exe"
C:\Program Files\Wireshark\tshark.exe
% exec $tsharkPath $sTsharkCmd > packet.log
tshark: The file " TestTShark.pcap  -Tfields -e ip.src" doesn't exist.
% eval exec $tsharkPath $sTsharkCmd > packet.log
couldn't execute "C:Program": no such file or directory

Since the path containing a space, while evaluating the code, Tcl treating C:\\Program as a program name and throwing the error. Then I managed to escape the space with backslash as follows, which worked then.

%  set tsharkPath "C:/Program\\ Files/Wireshark/tshark.exe"
C:/Program\ Files/Wireshark/tshark.exe
% eval exec $tsharkPath $sTsharkCmd > packet.log
% type packet.log
20.0.0.5
%

I am just curious. Is there any other option to handle this scenario ? Same problem observed with {*} also.

Answer 1

Your problem is that you're wanting space to be a part of an argument taken from variable, but to separate arguments coming from another argument. Tcl by default will try to apply the same uniform rules to all arguments: you need to do something extra to change that.

You want to use expansion of an argument. Your command

% eval exec $tsharkPath $sTsharkCmd > packet.log

Should be written as:

% exec $tsharkPath {*}$sTsharkCmd > packet.log

See how it is shorter? It's safer too. Try to avoid eval unless you really are doing something very complicated. (I hardly ever need it in my code…)

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If you're stuck with an ancient version of Tcl without {*} , you need to do this instead:

% eval [linsert $sTsharkCmd 0 exec $tsharkPath > packet.log]

Which is horribly non-obvious, or this:

% eval {exec $tsharkPath} $sTsharkCmd {> packet.log}

Which isn't too nice either (and it's easy to forget to get it quoted right).

Answer 2

eval [list exec $tsharkPath {*}$sTsharkCmd]

使用sTsharkCmd属性分隔的新命令进行评估...