Take notes on Linux private food from laruence (6)-filters, input and output, and pipelines

I. application tools in the filter Linux system are divided into three types: the interactive tool, the filter editor, which can accept data and filter and output the data. these tools are called filters and processes, there are input source and output objects. 2. input, output, and redirect input: filter

I. filter

There are three types of application tools in Linux:
Interactive tools
Filter
Editor
A tool that can accept data and filter and output data is called a filter.

There are input source and output objects for filters and processes.

II. input, output, and redirection

Input: data source of the filter

-- Standard input stdin (0): default value: Keyboard

Output: data destination of the filter

-- Stdout (1): terminal screen by default

Error output: the error message follows a different I/O channel from the standard output.

-- Stderr (2) for standard error output: terminal screen by default

Redirection: standard input, output, and error output can all be changed using specific symbols.

III. input redirection

Use "<" to redirect the input source

Most tools use the following file name as the input source.

Some filters must be added to specify the input source.

Cmond <file (reads files from the keyboard input)

As shown above, replace all uppercase characters in. pash_profile with lowercase characters.

IV. input from current document

Use <to enable the system to input all the input on the keyboard at a time, first send it to the virtual "current document", and then enter the input at a time.

A letter, symbol, or string is required as the start identifier.

You can select any symbol as the start identifier.

5. output redirection

Use> Change data output target

Example: ls-l> listfile

Display the files in the current directory in long mode and write them to the listfile file.

All existing file content will be deleted

VI. coverage and append

Use> to redirect the output. The original content of the file will be overwritten.

Ls-l> listfile

Use> to add output to a file

Ls-l> listfile

VII. Error output redirection

System errors are different from standard output I/O pipelines

By default, system errors are displayed on the terminal screen.

Use 2> redirect error messages to a file

Find/-type s 2>/dev/null

Use 2> add an error message to a file

Find/-name passwd 2> results

8. Dual output redirection

Use> and 2> to send the correct and incorrect input of an operation separately to different places:

Find/-perm-2 2> error> results

Use &> to send all input to the same place:

Find/-perm + 6000> file

Another method

9. pipelines

Use | directly sends the output of the previous filter to the input of the next filter

Ls-l | grep pass

Allow multiple pipelines

Note that the output of the filter before the MPs queue matches the input data type of the MPs queue filter.

10. common examples of redirection and pipelines

Ls-l | more

Display files in the current directory on the split screen

Cat <filea> fileb

Copy filea to fileb

Cat file. *> file

Merge several small files into one file