using awk in tcl script

Question

I want to print a particular column number fields in a file while in TCL script.

I tried with exec awk '{print $4}' foo where foo is filename, but it is not working as it gives error

can't read "4": no such variable

How can I do above awk in tcl scripting?

Thanks,

glenn jackman · Accepted Answer · 2013-06-07 18:02:39Z

14

The problem is that single quotes have no special meaning in Tcl, they're just ordinary characters in a string. Thus the $4 is not hidden from Tcl and it tries to expand the variable.

The Tcl equivalent to shell single quotes are braces. This is what you need:

exec awk {{print $4}} foo

The double braces look funny, but the outer pair are for Tcl and the inner pair are for awk.

Btw, the Tcl translation of that awk program is:

set fid [open foo r]
while {[gets $fid line] != -1} {
    set fields [regexp -all -inline {\S+} $line]
    puts [lindex $fields 3]
}
close $fid

answered Jun 7, 2013 at 18:02

glenn jackman

249k42 gold badges233 silver badges363 bronze badges

Sign up to request clarification or add additional context in comments.

4 Comments

Donal Fellows Over a year ago

Perfect answer. Awk is perfectly usable from Tcl, as is sed — and sometimes that's the easiest way to do things — but you have to remember that Tcl's syntax is not the same as that of a normal Unix shell. Why does Tcl use braces instead of single quotes? Because they're trivially nestable.

egorulz Over a year ago

% exec [cat log.file | awk {{print $1}}] can't read "1": no such variable while evaluating {exec [cat log.file | awk {{print $1}}]} Doesn't seem to work for me, am I doing something stupid? Or is there a caveat to the answer?

egorulz Over a year ago

I'm using tcl 8.4.5 in case that is of relevance.

egorulz Over a year ago

This does work, so I am guessing the square braces are trying to evaluate the variable. % exec head log.file | awk {{print $1}} Jun Jun Jun Jun Jun Jun Jun Jun Jun

Collectives™ on Stack Overflow

using awk in tcl script

1 Answer 1

4 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

4 Comments

Your Answer

Sign up or log in

Post as a guest

Related