. Using a combination of commands - to separate multiple commands
separated by sequential 1.
● Use good points
- Command 1; 2 command; Command 3
- sequentially performed, only has no logical relationship
2. Logical "and" partition
● Use &&
- Command 1 Command 2 && && command .... 3
- logical relationship "And" (and), all of the desired commands may be successfully performed
- if they fail, the subsequent command is not executed
3. The logical "or" spacer
● Use ||
- || command command. 1 2 3 ... || command
- logical relationship "or" (or), a command is successfully meets any desired
- just in front of the command fails when, subsequent commands will be executed
Examples of applications
for the case of pre-order failed to set additional terms
4. The determination operation
● combinatorial logical partition
- Command 1 Command 2 || command && 3
- 1 When the command is executed successfully things, will continue to execute the command 2 (skip command 3)
- when a command fails, the command will continue to 3 (ignore command 2)
Second, the role of the pipeline
● screen output of the command to make the command end treatment
- Command 1 | command 2 | 3 ... command
- the command to follow-up the text to be able to handle correctly, otherwise no objection
Third, the use of a combination of command - marked input and output
Everything is a file
● Linux basic idea
- a regular file, directory, keyboard, mouse ... all in the form of documents
- To access the hardware device, you must find the corresponding device file
I / O switching device
● standard input: receiving data from a user input device
● standard output: report from this device to the user's normal command output
● standard error: This device reported in the error information
| Types of | Device file | File Description No. | Default Device |
|---|---|---|---|
| Standard Input | /dev/stdin | 0 | keyboard |
| Standard output | /dev/stdout | 1 | monitor |
| Standard error output | /dev/stderr | 2 | monitor |
stdout and stderr
● execution results for the command
- run successfully, the screen information is reported to stdout equipment
- fail, the screen information is reported to stderr device
Fourth, what is redirected
● I re-enacted direction command / O devices
- NA default keyboard, monitor
- switch to the specified text file
Type redirection
● The I / O direction and the class discrimination
Redirect input
● keyboard input -> File Input
For instance, when applicable mail command to send email -
Redirect input
● output to a display -> output to a file
when, for example, you need to save the output of a command given result -
Mixing redirection
● normal, error output, respectively / combined redirection
- for example, need to distinguish between command output, and outputs the information and or