Awk command in Tcl foreach loop - loops

Question

I need to pass a variable value to awk command used in tickle.
Goal : i want to extract fisrt field of file clk_gate_names one by one in loop.So this is small example shown the same concept have benn used in one script.
one testcase below:
set a 0
incr a
foreach i {0.. 11} { # i variable is used for another thing
set test [exec awk {NR==${a}{print $1}} clk_gate_names]
}
Getting below error:
awk: NR==${a}{print $1}
awk: ^ syntax error
Please throw some light here. Thanks in advance :)

Answer 1

The problem is that you're wanting to mix variables from Tcl and variables from Awk. That's a bit complicated, as they are necessarily separate processes.
One option is to use Tcl's format command to build the Awk script-let.
set a 0
incr a
foreach i {0.. 11} { # i variable is used for another thing
set awkcode [format {NR==%d {print $1}} $a]
set test [exec awk $awkcode clk_gate_names]
}
However, a better approach is to pass the variable in by the -v option. That has the advantage of being not easily confused by any weird quoting going on, and Tcl doesn't break words unexpectedly (except, in exec, when it looks like a file/pipe redirection; that's a wart).
set a 0
incr a
foreach i {0.. 11} { # i variable is used for another thing
set test [exec awk -v a=$a {NR==a {print $1}} clk_gate_names]
}
The third way is to use an environment variable. That has the advantage of not being susceptible to the problems with redirections (so you can pass in values containing > for example).
set a 0
incr a
foreach i {0.. 11} { # i variable is used for another thing
set env(A_FROM_TCL) $a
set test [exec awk {NR==$ENVIRON["A_FROM_TCL"] {print $1}} clk_gate_names]
}
Notes:
Remember with awk and Tcl, don't use single quotes. Tcl doesn't use the same syntax as bash. Put the script in braces always or you'll get very confused.
I assume you know about the syntax of foreach? For the purposes of our discussion here it's not important, but you'd probably be having problems from it if the code you posted is exactly what you are using…

Answer 2

try below logic -
awk -v a=1 'NR==a {print $1}' f
As per your code -
set a 0
incr a
foreach i {0.. 11} { # i variable is used for another thing
set test [exec awk -v a="$a" 'NR==a {print $1}' clk_gate_names]
}
let me know if it satisfy your req. and share the output(desired output/error)

Answer 3

awk -v a=${a} "NR==a{print \$1}" filename
Check :
http://phaseit.net/claird/comp.lang.tcl/fmm.html
AWK: who | awk '{ print $1 }' works from the command line, but my Tcl interpreter rejects exec who | awk '{ print $1 }' I often hear
that from people who haven't yet learned to ask tclsh to interpret
exec who | awk {{ print $1 }} Notice that the '-s aren't "about" awk;
they're just conventional quoting in the shells from which one most
often accesses awk. exec doesn't use the shells. {} perform an
analogous function of quoting for Tcl. More examples appear in this
Google thread. Alexandre Ferrieux gives a correct and concise
explanation in another thread. The problem at hand for him happened to
do with sed, but that's essentially inconsequential; the command-line
syntaxes of awk and sed exhibit identical symptoms. Briefly, as the
error messages which arise themselves say, the single quotes (') are
the problem. These are shell markup for strings which shall not be
substituted. /bin/sh and others remove this markup before calling awk.
In Tcl, in contrast, braces {} serve the same purpose. Braces have the
advantage that they can be nested. One conclusion: brace the braces
that awk expects: awk -F " " {{print $1}}. Note that, in this last, it
is not necessary to escape the dollar-sign, because the outer brace
protect it, too.
Much the same has been written several times by Richard Suchenwirth,
Mark Janssen, Kevin Kenny, and others; it's unlikely any particular
expression was invented in isolation.