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Editor to share with you what are the BASH commands in Docker, I believe most people do not know much about it, so share this article for your reference, I hope you can learn a lot after reading this article, let's go to know it!

Basic syntax:

Syntax description > output redirection. Save the standard output (stdout) executed by the command as a file. The OS of the Unix series treats the device as a file, so we can send the result of the command execution to a specific device: $echo "hello" >. / hello.txt $echo "hello" > / dev/null > add the standard output (stdout) of the command execution to the file. The difference between ">" and ">" is that ">" will overwrite the original contents of the file, while "> >" will only add the content to the end of the existing file $echo "world" >. / hello.txt2 > bash, respectively, the three numbers represent STDIN_FILENO, STDOUT_FILENO, STDERR_FILENO, that is, standard input (usually keyboard), standard output (user terminal console), standard error (error information output). The function of 2 > is to save the standard error (stderr) of command execution as a file 2 > > to add the standard error (stderr) of command execution to the file & > to save all standard output and standard error as file 1 > & 2 to mark standard output as standard error. The final output of the following code is empty because we marked the standard output as standard error. $hello=$ (echo "hello world" 1 > & 2) $echo hello2 > & 1 sends standard error as standard output. Take a look at the following example: $execnofile > / dev/null 2 > & 1 We execute a file that does not exist locally, and then send the output to the empty device. Since we mark standard error as standard output, there will be no content output at the end of the day | pipe command. Send the standard output of the first execution command as the standard input of other commands, our common use is like $ps-ef\ | grep mysql$Bash variables, storage variables do not need to use the $symbol, input or use variables need the $symbol, for example: $() the result of the execution of a command variable. Store the execution result of the command to a variable or pass it to another command as a parameter, for example: & & run multiple commands on one line, but the latter will take effect only if the previous command is executed successfully. $make & & make install; also runs multiple commands on one line, and the difference from the above command is that even if the first command fails, the following command is executed, for example, the''string. The system does not process variables in'', only using variable names, for example:

"" is similar to'', except that if there is a variable in "", the output is replaced with the content of the variable. " Example:

${} function 1: variable substitution, mainly used to output variables in the "" string, or use $instead, for example: action 2: set the default variable in the script, see the following example for the first time, I created a hello variable, where the value of hello is null Hello= ${hello- "my"} means that if the hello variable does not exist, the value "my" is assigned to hello, and if hello already exists, the default value is used, so you can see in the output result that the output is the default value of hello, null The second time, hello= ${hello:- "my"} means that if there is a value in the variable that is not empty, the current value is used, and if the current value is empty, "my" is used, so we see the output as "my"\ to write one line of command as multiple lines {starting numbers. The last number} is used to express a consecutive number, for example: ifif conditional statement, used to compare variables or strings, specific usage: if {$a-eq $b}; then echo $a fi. Compare numbers using:-eq: equal to-ne: not equal to-gt: greater than-ge: greater than or equal to-lt: less than-le: less than or equal to comparison string can be used: =, = =: the same! =: different-z: the string is NULL-n: the string is not a NULLforfor loop statement, for example: whilewhile loop, example:

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