Shell keyword 「trap」
type trap
執行
$ type trap顯示
trap is a shell builtinhelp trap
執行
$ help trap顯示
trap: trap [-lp] [[arg] signal_spec ...]
Trap signals and other events.
Defines and activates handlers to be run when the shell receives signals
or other conditions.
ARG is a command to be read and executed when the shell receives the
signal(s) SIGNAL_SPEC. If ARG is absent (and a single SIGNAL_SPEC
is supplied) or `-', each specified signal is reset to its original
value. If ARG is the null string each SIGNAL_SPEC is ignored by the
shell and by the commands it invokes.
If a SIGNAL_SPEC is EXIT (0) ARG is executed on exit from the shell. If
a SIGNAL_SPEC is DEBUG, ARG is executed before every simple command. If
a SIGNAL_SPEC is RETURN, ARG is executed each time a shell function or a
script run by the . or source builtins finishes executing. A SIGNAL_SPEC
of ERR means to execute ARG each time a command's failure would cause the
shell to exit when the -e option is enabled.
If no arguments are supplied, trap prints the list of commands associated
with each signal.
Options:
-l print a list of signal names and their corresponding numbers
-p display the trap commands associated with each SIGNAL_SPEC
Each SIGNAL_SPEC is either a signal name in <signal.h> or a signal number.
Signal names are case insensitive and the SIG prefix is optional. A
signal may be sent to the shell with "kill -signal $$".
Exit Status:
Returns success unless a SIGSPEC is invalid or an invalid option is given.範例001
執行
$ trap -l顯示
1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL 5) SIGTRAP
6) SIGABRT 7) SIGBUS 8) SIGFPE 9) SIGKILL 10) SIGUSR1
11) SIGSEGV 12) SIGUSR2 13) SIGPIPE 14) SIGALRM 15) SIGTERM
16) SIGSTKFLT 17) SIGCHLD 18) SIGCONT 19) SIGSTOP 20) SIGTSTP
21) SIGTTIN 22) SIGTTOU 23) SIGURG 24) SIGXCPU 25) SIGXFSZ
26) SIGVTALRM 27) SIGPROF 28) SIGWINCH 29) SIGIO 30) SIGPWR
31) SIGSYS 34) SIGRTMIN 35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3
38) SIGRTMIN+4 39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8
43) SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7
58) SIGRTMAX-6 59) SIGRTMAX-5 60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2
63) SIGRTMAX-1 64) SIGRTMAX或是執行
$ kill -l範例002
執行
$ trap -p顯示
trap -- '' SIGTSTP
trap -- '' SIGTTIN
trap -- '' SIGTTOU範例003
signal.sh
#!/usr/bin/env bash
trap "echo got signal!" SIGHUP SIGINT
while true; do
date;
sleep 1;
done設定可執行
$ chmod u+x signal.sh執行
$ ./signal.sh另外開啟一個Terminal
找到剛剛執行的pid
執行
$ ps aux | grep signal.sh或是執行
$ pgrep -f ./signal.sh可以找到pid，例如
15060然後對這個process發送signal
執行
$ kill -1 15060或是執行
$ kill -2 15060就會在一開始執行 signal.sh 那個 Terminal
看到
got signal!
Tue May 17 20:47:13 CST 20
...略...上面的的步驟，也可以直接改成執行下面的指令
執行
$ pkill -1 -f ./signal.sh或是執行
$ pkill -2 -f ./signal.sh然後執行下面的指令，把剛剛執行的「./signal.sh」關閉
執行
$ pkill -9 -f ./signal.sh或是執行
$ kill -9 15060範例004
server.sh
#!/usr/bin/env bash
THE_SIG_HUP=0
handle_signal () {
if [ $THE_SIG_HUP = 0 ]; then
THE_SIG_HUP=1;
else
THE_SIG_HUP=0;
fi
}
trap handle_signal SIGHUP
while true; do
#echo $THE_SIG_HUP;
if [ $THE_SIG_HUP = 1 ]; then
echo 'idle';
else
date;
fi
sleep 1;
done設定為可執行
$ chmod u+x server.sh執行
$ ./server.sh顯示
Tue May 17 20:56:44 CST 2016
Tue May 17 20:56:45 CST 2016
Tue May 17 20:56:46 CST 2016
Tue May 17 20:56:47 CST 2016然後執行
$ pkill -1 -f ./server.sh就會顯示
Tue May 17 20:56:48 CST 2016
idle
idle
...略...然後再執行
$ pkill -1 -f ./server.sh就會改成
idle
Tue May 17 20:58:30 CST 2016
Tue May 17 20:58:31 CST 2016
Tue May 17 20:58:32 CST 2016
...略...