Calling SED using exec in TCL

[lac]

Hi,

I have been trying to call SED from TCL using the exec function and it
behaves differently then if I called the same SED function from the
shell (command line).

I am trying to extract only certain lines from a file as follow:

sed -n '5,10p' $Filename

If I type this from the command line in ksh, I get what I expect, lines
5 to 10 are printed to standard output.

However, if I try to call that same function within TCL using exec,
nothing returns.

catch {exec ksh -c "sed '5,10p' $Filename"} content

I have tried not using -n on sed but then all the file gets printed to
standard output when called from command line with duplicates of lines
5 to 10. When I don't use the -n flag from withing TCL (with exec), all
the file is printed without duplicates of line 5 to 10.

Can someone help me with this? I don't understand what is happening
here?

Thank you,

lac

[Cameron Laird]

In article <1148414050.1...@i39g2000cwa.googlegroups.com>,

lac <luc.c...@gmail.com> wrote:
>Hi,
>
>I have been trying to call SED from TCL using the exec function and it
>behaves differently then if I called the same SED function from the
>shell (command line).
>
>I am trying to extract only certain lines from a file as follow:
>
>sed -n '5,10p' $Filename
>
>If I type this from the command line in ksh, I get what I expect, lines
>5 to 10 are printed to standard output.
>
>However, if I try to call that same function within TCL using exec,
>nothing returns.
>
>catch {exec ksh -c "sed '5,10p' $Filename"} content
>
>I have tried not using -n on sed but then all the file gets printed to
>standard output when called from command line with duplicates of lines
>5 to 10. When I don't use the -n flag from withing TCL (with exec), all
>the file is printed without duplicates of line 5 to 10.

.
.
.
I don't understand your description. When I command

catch {exec ksh -c "sed -n '5,10p' $Filename"} content

I see the five lines I expect in $content.

There are several other possibilities. You might like

set content [exec sed -n 5,10p $Filename]

[SM Ryan]

"lac" <luc.c...@gmail.com> wrote:
# Hi,
#
# I have been trying to call SED from TCL using the exec function and it
# behaves differently then if I called the same SED function from the
# shell (command line).
#
# I am trying to extract only certain lines from a file as follow:
#
# sed -n '5,10p' $Filename
#
# If I type this from the command line in ksh, I get what I expect, lines
# 5 to 10 are printed to standard output.
#
# However, if I try to call that same function within TCL using exec,
# nothing returns.
#
# catch {exec ksh -c "sed '5,10p' $Filename"} content

You shouldn't need to use ksh; and if $Filename contains shell
special characters, it will not work. You should be able to do
catch {exec sed {5,10p} $Filename} content

You should only call a shell -c through exec if there some kind
of shell processing of the command string you need that you cannot
(conveniently) do in Tcl.

--
SM Ryan http://www.rawbw.com/~wyrmwif/
I hope it feels so good to be right. There's nothing more
exhilarating pointing out the shortcomings of others, is there?

[lac]

Thank you for your replies.

I found that when I use the following line, it behaves like I want it
too:

set content [exec sed -n 5,10p tools.wish]

where tools.wish is my filename.

Now if I want to set the start and end lines dynamically as follows, it
doesn't work (or returns an empty string)

set start 5
set end 10
set content [exec sed -n ${start},${end}p tools.wish]

I am lost! Thanks for helping,

lac

[Arjen Markus]

Works perfectly for me ... Is the file that long?
What is the value of errorInfo?

Regards,

Arjen

[neil mckay]

Is there any reason for not doing this in straight Tcl? The code's a
little longer than exec'ing sed, but it eliminates an external
dependency. Try this proc:

proc picklines {fname startline endline} {
if {[catch [list open $fname "r"] fd] != 0} {
return [list]
}

set linelist [list]

set lineNo 0
while {$lineNo < $endline} {
set nChars [gets $fd line]
if {$nChars < 0} {
return $linelist
}
incr lineNo
if {$lineNo >= $startline} {
lappend linelist $line
}
}

close $fd

return $linelist
}

Neil

[neil mckay]

Oops, I forgot one thing: if the picklines proc returns before getting
all the lines, it needs to close the file. Replace

if {$nChars < 0} {
return $linelist
}

with

if {$nChars < 0} {

[lac]

Thank You Neil,

I tried using your solution and it seems to be as fast as using sed.

lac