In the above results, in front of the line "+" sign is a shell script commands actually executed, in front of the line "+" sign is to perform the command specified trap mechanism, the other line is output.
In addition to the shell execution options can be specified at boot shell, but also in a script using the set command to specify. "Set - the parameter" means enable an option, "set + parameter" means to close an option. Sometimes we do not need to keep track of all the command line when you start with the "-x" option, then we can use the set command in a script, as shown in the following script fragment:
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set -x #启动"-x"选项
要跟踪的程序段
set +x #关闭"-x"选项
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