bash:redirection
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| bash:redirection [2019/12/14 19:44] – peter | bash:redirection [2021/01/13 21:51] (current) – [BASH - Redirection] peter | ||
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| Every File has an associated number called File Descriptor (FD). | Every File has an associated number called File Descriptor (FD). | ||
| - | Your screen | + | * Your screen has a File Descriptor. |
| + | * Your printer has a File Descriptor. | ||
| - | If the output is sent to File Descriptor of the printer, the program output would have been printed. | + | ---- |
| - | Standard File Descriptor: | + | ===== Standard File Descriptors ===== |
| - | ^File^File Descriptor^ | + | Whenever you execute a program/ |
| - | |Standard Input STDIN|0| | + | |
| - | |Standard Output STDOUT|1| | + | |
| - | |Standard Error STDERR|2| | + | |
| + | These files are always present whenever a program is run. | ||
| + | ^File^File Descriptor^ | ||
| + | |Standard Input STDIN|0| | ||
| + | |Standard Output STDOUT|1| | ||
| + | |Standard Error STDERR|2| | ||
| - | |||
| - | |||
| - | |||
| - | Every file in Linux has a corresponding File Descriptor associated with it. | ||
| The keyboard is the standard input device while your screen is the standard output device. | The keyboard is the standard input device while your screen is the standard output device. | ||
| - | Summary: | + | However, files can have their input and output redirected, using: |
| * ">" | * ">" | ||
| Line 33: | Line 32: | ||
| * ">&" | * ">&" | ||
| * Errors can be re-directed using its corresponding File Descriptor 2. | * Errors can be re-directed using its corresponding File Descriptor 2. | ||
| - | |||
| ---- | ---- | ||
| Line 83: | Line 81: | ||
| ---- | ---- | ||
| - | ===== File Descriptors (FD) ===== | + | ===== Error Redirection ===== |
| - | + | ||
| - | In Linux/Unix, everything is a file. | + | |
| - | + | ||
| - | Regular file, Directories, | + | |
| - | + | ||
| - | Every File has an associated number called File Descriptor (FD). | + | |
| - | + | ||
| - | Your screen also has a File Descriptor. | + | |
| - | + | ||
| - | When a program is executed the output is sent to File Descriptor of the screen, and you see program output on your monitor. | + | |
| - | + | ||
| - | If the output is sent to File Descriptor of the printer, the program output would have been printed. | + | |
| - | + | ||
| - | ---- | + | |
| - | + | ||
| - | ==== Error Redirection ==== | + | |
| - | + | ||
| - | Whenever you execute a program/ | + | |
| - | + | ||
| - | ---- | + | |
| - | + | ||
| - | These files are always present whenever a program is run. | + | |
| - | + | ||
| - | As explained before a file descriptor, is associated with each of these files: | + | |
| - | + | ||
| - | ^File^File Descriptor^ | + | |
| - | |Standard Input STDIN|0| | + | |
| - | |Standard Output STDOUT|1| | + | |
| - | |Standard Error STDERR|2| | + | |
| - | + | ||
| - | By default, error stream is displayed on the screen. | + | |
| - | + | ||
| - | Error redirection is routing the errors to a file other than the screen. | + | |
| - | + | ||
| - | ==== Why Error Redirection? | + | |
| Error re-direction is one of the very popular features of Unix/Linux. | Error re-direction is one of the very popular features of Unix/Linux. | ||
| Line 129: | Line 92: | ||
| The solution is to re-direct the error messages to a file. | The solution is to re-direct the error messages to a file. | ||
| - | === Example 1 === | + | ==== Example 1 ==== |
| <code bash> | <code bash> | ||
| Line 145: | Line 108: | ||
| ---- | ---- | ||
| - | === Example 2 === | + | ==== Example 2 ==== |
| - | + | ||
| - | Here is another example which uses find statement - | + | |
| <code bash> | <code bash> | ||
bash/redirection.1576352694.txt.gz · Last modified: 2020/07/15 10:30 (external edit)