Unix command does not work in Tcl script

Question

I'm new to Tcl and UNIX programming.

The following command works on the UNIX command-lines, but doesn't work in a Tcl script.

$ sort -b -k8  abc.txt | awk '!a[$1]++'
error out for 8 (-k8) and 1($1) is not variable

I'm trying to sort on Column 8 first and then pick only unique data on column 1.

I'm also trying to save data into a file.

Answer 1

I think you need to escape [] and $ in the string, eg:

send_unix_cmd "sort -k$sort_col top_$host | awk '!a\[\$$uni_col\]++' "

I also removed the {}.

Answer 2

I thing for executing command in Tcl script you should use exec. And single quotes have no special meaning in Tcl script so it will try to expand the variable $1. You can try following:

exec sort -b -k8  abc.txt | awk {!a[$1]++} > output

If you don't redirect the standard output of the program, it becomes the return value of the exec command, so you can capture it for example:

set result [exec sort -b -k8  abc.txt | awk {!a[$1]++}]