我使用过的Linux命令之trap - 在脚本中处理信号

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用途说明

rap是一个shell内建命令，它用来在脚本中指定信号如何处理。比如，按Ctrl+C会使脚本终止执行，实际上系统发送了SIGINT信号给脚本进程，SIGINT信号的默认处理方式就是退出程序。如果要在Ctrl+C不退出程序，那么就得使用trap命令来指定一下SIGINT的处理方式了。trap命令不仅仅处理Linux信号，还能对脚本退出（EXIT）、调试（DEBUG）、错误（ERR）、返回（RETURN）等情况指定处理方式。

常用参数

?????? trap [-lp] [[arg] sigspec ...]

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格式：trap "commands" signals

当shell接收到signals指定的信号时，执行commands命令。（The? command arg is to be read and executed when the shell receives signal(s) sigspec. ）

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格式：trap signals

如果没有指定命令部分，那么就将信号处理复原。比如 trap INT 就表明恢复Ctrl+C退出。（If arg is absent (and there is a single sigspec) or -, each specified signal is reset to its? original? disposition? (the value? it? had? upon? entrance? to? the? shell). ）

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格式：trap "" signals

忽略信号signals，可以多个，比如 trap "" INT 表明忽略SIGINT信号，按Ctrl+C也不能使脚本退出。又如 trap "" HUP 表明忽略SIGHUP信号，即网络断开时也不能使脚本退出。（If arg is the null string the signal specified by each sigspec is ignored by the shell and by the commands it invokes. ）

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格式：trap -p

格式：trap -p signal

把当前的trap设置打印出来。（If arg is not present and -p? has? been supplied,? then? the trap commands associated with each sigspec are displayed.? If no arguments are supplied or if only -p is given, trap prints the list of commands associated? with? each? signal.）

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格式：trap -l

把所有信号打印出来。（The? -l option? causes? the shell to print a list of signal names and their corresponding numbers.? Each sigspec is either a signal name defined in <signal.h>, or a signal number.? Signal names? are? case? insensitive and? the? SIG prefix is optional.）?

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格式：trap "commands" EXIT

脚本退出时执行commands指定的命令。（If a sigspec is EXIT (0) the command arg is executed on exit from the shell.）

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格式：trap "commands" DEBUG

在脚本执行时打印调试信息，比如打印将要执行的命令及参数列表。（If a sigspec is DEBUG, the command arg is executed before every? simple? command,? for? command, case? command,? select command, every arithmetic for command, and before the first command executes in a shell function (see SHELL GRAMMAR above).? Refer to the description of the extdebug option to the? shopt builtin? for? details of its effect on the DEBUG trap.）

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格式：trap "commands" ERR

当命令出错，退出码非0，执行commands指定的命令。（If a sigspec is ERR, the command arg is executed whenever a simple command has a non-zero exit status, subject to the following conditions.? The ERR trap is not executed if the failed command is part of the command list immediately following a while or until keyword, part of the test in an if statement, part of a && or ┅Ι│ list, or if the command’s return? value is? being? inverted via !.? These are the same conditions obeyed by the errexit option.）

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格式：trap "commands" RETURN

当从shell函数返回、或者使用source命令执行另一个脚本文件时，执行commands指定的命令。（If a sigspec is RETURN, the command arg is executed each time a shell function or a script executed with the . or source??? builtins? finishes? executing.?? Signals? ignored? upon? entry? to the shell cannot be trapped or reset. Trapped signals that are not being ignored are reset to their original values in a child process when it is created.? The return status is false if any sigspec is invalid; otherwise trap returns true.）

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使用示例

示例一

[root@new55 ~]# trap -p
[root@new55 ~]# trap "echo hello" INT
[root@new55 ~]# trap -p
trap -- 'echo hello' SIGINT
[root@new55 ~]# trap -p INT
trap -- 'echo hello' SIGINT
[root@new55 ~]# trap -p QUIT

[root@new55 ~]# Ctrl+C

[root@new55 ~]#