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Top Forums UNIX for Advanced & Expert Users Trapping a kill command sent to a script and using it to send an EOF to a subprocess before killing Post 302880587 by jim mcnamara on Friday 20th of December 2013 07:13:00 PM
Old 12-20-2013
You need a source of active subprocesses. ptree is available in Solaris, for example.
Linux has /proc/[pid]/ppid. pstree uses this to draw ascii "graphics".

So what OS?

The bash trap statement you want: a function + two trap statements

Code:
zap()  # some method of getting all active children/grandchildren, etc. Assume a file
{
    # turn off trap
    trap - SIGTERM 
    # kill the kids
    me=$$
    while read pid
    do
        if [ $$ -ne  $pid ] ; then   # if active kill the process
           kill -0 $pid && kill $pid
        fi
   done < a_file_with_childrens_pids
}

# enable zap
trap ' zap ' SIGTERM

Bash kill builtin also supports using jobs, so you can use the jobs command to list active children - if they do not have descendants.

Notice there is a very small possibility of a race condition when several SIGTERM (default signal for kill) signals are received at once. In that case zap() will not complete.

You need a way to enumerate children. You can remember their pids in an array or a file or some other object maybe.
If one of the children is "extinct", you did not rembmer that, and the pid is being used by some hapless process - then you have problems. Another race condition. Especially if this stuff runs as root. On linux or solaris you can evaluate the correctness of the pid by querying proc or getting the uid. - maybe like what exe is the potential kid running. If root is running zap() and you run, be sure to keep a tight handle on current active descendant processes. Or you could clobber your own payroll job.

Last edited by jim mcnamara; 12-20-2013 at 08:20 PM..
 

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SCRIPT(1)							   User Commands							 SCRIPT(1)

NAME
script - make typescript of terminal session SYNOPSIS
script [options] [file] DESCRIPTION
script makes a typescript of everything displayed on your terminal. It is useful for students who need a hardcopy record of an interactive session as proof of an assignment, as the typescript file can be printed out later with lpr(1). If the argument file is given, script saves the dialogue in this file. If no filename is given, the dialogue is saved in the file type- script. OPTIONS
-a, --append Append the output to file or to typescript, retaining the prior contents. -c, --command command Run the command rather than an interactive shell. This makes it easy for a script to capture the output of a program that behaves differently when its stdout is not a tty. -e, --return Return the exit code of the child process. Uses the same format as bash termination on signal termination exit code is 128+n. -f, --flush Flush output after each write. This is nice for telecooperation: one person does `mkfifo foo; script -f foo', and another can supervise real-time what is being done using `cat foo'. --force Allow the default output destination, i.e. the typescript file, to be a hard or symbolic link. The command will follow a symbolic link. -q, --quiet Be quiet (do not write start and done messages to standard output). -t[file], --timing[=file] Output timing data to standard error, or to file when given. This data contains two fields, separated by a space. The first field indicates how much time elapsed since the previous output. The second field indicates how many characters were output this time. This information can be used to replay typescripts with realistic typing and output delays. -V, --version Display version information and exit. -h, --help Display help text and exit. NOTES
The script ends when the forked shell exits (a control-D for the Bourne shell (sh(1)), and exit, logout or control-d (if ignoreeof is not set) for the C-shell, csh(1)). Certain interactive commands, such as vi(1), create garbage in the typescript file. script works best with commands that do not manipulate the screen, the results are meant to emulate a hardcopy terminal. It is not recommended to run script in non-interactive shells. The inner shell of script is always interactive, and this could lead to unexpected results. If you use script in the shell initialization file, you have to avoid entering an infinite loop. You can use for example the .profile file, which is read by login shells only: if test -t 0 ; then script exit fi You should also avoid use of script in command pipes, as script can read more input than you would expect. ENVIRONMENT
The following environment variable is utilized by script: SHELL If the variable SHELL exists, the shell forked by script will be that shell. If SHELL is not set, the Bourne shell is assumed. (Most shells set this variable automatically). SEE ALSO
csh(1) (for the history mechanism), scriptreplay(1) HISTORY
The script command appeared in 3.0BSD. BUGS
script places everything in the log file, including linefeeds and backspaces. This is not what the naive user expects. script is primarily designed for interactive terminal sessions. When stdin is not a terminal (for example: echo foo | script), then the session can hang, because the interactive shell within the script session misses EOF and script has no clue when to close the session. See the NOTES section for more information. AVAILABILITY
The script command is part of the util-linux package and is available from Linux Kernel Archive <https://www.kernel.org/pub/linux/utils /util-linux/>. util-linux June 2014 SCRIPT(1)
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