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What does `set -x` do?

 Take a look: 

help set
help -m set | less

set -x enables a mode of the shell where all executed commands are printed to the terminal. In your case it‘s clearly used for debugging, which is a typical use case for set -x: printing every command as it is executed may help you to visualize the control flow of the script if it is not functioning as expected.

set +x disables it.

https://stackoverflow.com/questions/36273665/what-does-set-x-do

What does set -e mean in a bash script?

 https://stackoverflow.com/questions/19622198/what-does-set-e-mean-in-a-bash-script

-e  Exit immediately if a command exits with a non-zero status.

文件比较运算符
-e filename 	如果 filename存在，则为真 	[ -e /var/log/syslog ]
-d filename 	如果 filename为目录，则为真 	[ -d /tmp/mydir ]
-f filename 	如果 filename为常规文件，则为真 	[ -f /usr/bin/grep ]
-L filename 	如果 filename为符号链接，则为真 	[ -L /usr/bin/grep ]
-r filename 	如果 filename可读，则为真 	[ -r /var/log/syslog ]
-w filename 	如果 filename可写，则为真 	[ -w /var/mytmp.txt ]
-x filename 	如果 filename可执行，则为真 	[ -L /usr/bin/grep ]
filename1-nt filename2 	如果 filename1比 filename2新，则为真 	[ /tmp/install/etc/services -nt /etc/services ]
filename1-ot filename2 	如果 filename1比 filename2旧，则为真 	[ /boot/bzImage -ot arch/i386/boot/bzImage ]
字符串比较运算符 （请注意引号的使用，这是防止空格扰乱代码的好方法）
-z string 	如果 string长度为零，则为真 	[ -z "$myvar" ]
-n string 	如果 string长度非零，则为真 	[ -n "$myvar" ]
string1= string2 	如果 string1与 string2相同，则为真 	[ "$myvar" = "one two three" ]
string1!= string2 	如果 string1与 string2不同，则为真 	[ "$myvar" != "one two three" ]
算术比较运算符
num1-eq num2 	等于	[ 3 -eq $mynum ]
num1-ne num2 	不等于	[ 3 -ne $mynum ]
num1-lt num2 	小于	[ 3 -lt $mynum ]
num1-le num2 	小于或等于	[ 3 -le $mynum ]
num1-gt num2 	大于	[ 3 -gt $mynum ]
num1-ge num2 	大于或等于	[ 3 -ge $mynum ]

shell命令

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原文地址：https://www.cnblogs.com/sinferwu/p/12723189.html