Execute piped shell commands in Tcl - shell

Question

I want to execute these piped shell commands in Tcl:
grep -v "#" inputfile | grep -v ">" | sort -r -nk7 | head
I try:
exec grep -v "#" inputfile | grep -v ">" | sort -r -nk7 | head
and get an error:
Error: grep: invalid option -- 'k'
When I try to pipe only 2 of the commands:
exec grep -v "#" inputfile | grep -v ">"
I get:
Error: can't specify ">" as last word in command
Update: I also tried {} and {bash -c '...'}:
exec {bash -c 'grep -v "#" inputfile | grep -v ">"'}
Error: couldn't execute "bash -c 'grep -v "#" inputfile | grep -v ">"'": no such file or directory
My question: how can I execute the initial piped commands in a tcl script?
Thanks

Answer 1

The problem is that exec does “special things” when it sees a > on its own (or at the start of a word) as that indicates a redirection. Unfortunately, there's no practical way to avoid this directly; this is an area where Tcl's syntax system doesn't help. You end up having to do something like this:
exec grep -v "#" inputfile | sh -c {exec grep -v ">"} | sort -r -nk7 | head
You can also move the entire pipeline to the Unix shell side:
exec sh -c {grep -v "#" inputfile | grep -v ">" | sort -r -nk7 | head}
Though to be frank this is something that you can do in pure Tcl, which will then make it portable to Windows too…

Answer 2

The > is causing problems here.
You need to escape it from tcl and the shell to make it work here.
exec grep -v "#" inputfile | grep -v {\\>} | sort -r -nk7 | head
or (and this is better since you have one less grep)
exec grep -Ev {#|>} inputfile | sort -r -nk7 | head
If you look in the directory you were running this from (assuming tclsh or similar) you'll probably see that you created an oddly named file (i.e. |) before.

Answer 3

In pure Tcl:
package require fileutil
set lines {}
::fileutil::foreachLine line inputfile {
if {![regexp #|> $line]} {
lappend lines $line
}
}
set lines [lsort -decreasing -integer -index 6 $lines]
set lines [lrange $lines 0 9]
puts [join $lines \n]\n
(-double might be more appropriate than -integer)
Edit: I mistranslated the (1-based) -k index for the command sort when writing the (0-based) -index option for lsort. It is now corrected.
Documentation: fileutil package, if, join, lappend, lrange, lsort, package, puts, regexp, set