28 lines
1.1 KiB
Markdown
28 lines
1.1 KiB
Markdown
---
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tags:
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- shell
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---
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# File descriptors
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File descriptors are shorthand for `stdin`, `stdout` and `stderr`:
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| File descriptor | Name | Common abbreviation |
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| --------------- | --------------- | ------------------- |
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| 0 | Standard input | `stdin` |
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| 1 | Standard output | `stdout` |
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| 2 | Standard error | `stderr` |
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They are typically used when you want to
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[redirect](Redirection.md) the output of the
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standard/input /output/error somewhere, e.g a file or as input to another
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program. A classic case is `[some_command] > /dev/null 2>&1`
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They are all technically "files" which are open and which append themselves to
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every process that can run in the shell. For any command or program that you
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run, you will be able to access `0`, `1` and `2` for them. In this way they are
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similar to variables like
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[`$0`](Passing_arguments_and_options_to_Bash_scripts.md#passing-arguments)
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and
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[`$@`](Passing_arguments_and_options_to_Bash_scripts.md#passing-arguments).
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They have a universal meaning within the context of the shell runtime.
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