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AWK doesn't accept TCL results with error awk: can't open file

I'm trying to get result of a ping from TCL in AWK with the following code:

set n [exec ping 8.8.8.8 -c 2]
exec awk {"NR>=2 && NR<=4 { print }"} $n

but I get this error:

Error in startup script: awk: can't open file PING 8.8.8.8 ...

it seems that AWK gets $n not as an input but as a file. I found this but although it seems the same question, I'm having different problem. I can RUN AWK inside my TCL. The problem is that it does't accept Input as a source from me and although I didn't us -f switch it still gets it as a file.

Solution

  • 2 choices come to mind

    1. hand over the ping output as the stdin to awk:

      set n [exec ping 8.8.8.8 -c 2]
exec awk {NR>=2 && NR<=4 { print }} << $n
# ..................................^^

      https://tcl.tk/man/tcl8.6/TclCmd/exec.htm

    2. don't bother with the temporary variable

      exec ping 8.8.8.8 -c 2 | awk {NR>=2 && NR<=4 { print }}

    You don't want the double quotes inside the braces: the braces are used to quote the awk body, and you don't want to pass the double quotes to awk.

    Another option: since you just want the 2nd through 4th lines of the ping output, use Tcl and you don't need awk at all:

    set ping [exec ping 8.8.8.8 -c 2]
set lines [lrange [split $ping \n] 1 3]
puts [join $lines \n]

    or unreadably

    puts [join [lrange [split [exec ping 8.8.8.8 -c 2] \n] 1 3] \n]