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Bash intro

#!/bin/bash

📄 Bash – Przekierowywanie wyjścia do plików i konsoli

W Bashu możesz przekierowywać wyjście poleceń na wiele sposobów:

  • do plików,
  • do konsoli,
  • jednocześnie do obu.

🔁 Przekierowania w Bashu

Sposób Opis Przykład
> Nadpisuje plik wyjściem stdout (standardowe wyjście) ls > plik.txt
>> Dopisuje wyjście stdout do istniejącego pliku ls >> plik.txt
2> Przekierowanie stderr (błędów) ls nieistnieje 2> blad.txt
2>> Dopisanie stderr do istniejącego pliku ls nieistnieje 2>> blad.txt
&> Przekierowanie stdout i stderr do jednego pliku ls * &> wszystko.txt
`command tee plik.txt` Wyświetla na ekranie i zapisuje do pliku (nadpisuje)
`command tee -a plik` Wyświetla na ekranie i dopisuje do pliku
command > /dev/null Wyłącza stdout ls > /dev/null
command 2> /dev/null Ukrywa błędy ls nieistnieje 2> /dev/null
command &> /dev/null Ukrywa wszystko (stdout + stderr) ls nieistnieje &> /dev/null

✅ Przykłady praktyczne

1. Zapis stdout do pliku

echo "Hello world!" > log.txt

2. Dopisanie stderr do pliku

ls nieistnieje 2>> errors.log

3. Zapis stdout i stderr razem

some_command &> full_output.log

4. Wyświetlanie na konsolę i zapisywanie do pliku

python3 skrypt.py | tee wynik.txt

5. Tylko stderr, bez stdout

command 1> /dev/null 2> error_only.log

💡 Dodatki

  • tee jest bardzo przydatne, gdy chcesz widzieć wynik na żywo i jednocześnie zapisywać go.
  • &> to skrót do 1> file 2>&1 — przekierowanie stdout oraz stderr razem.

OLD

      || visible in terminal ||   visible in file   || existing

Syntax || StdOut | StdErr || StdOut | StdErr || file
==========++==========+==========++==========+==========++=========== > || no | yes || yes | no || overwrite >> || no | yes || yes | no || append || | || | || 2> || yes | no || no | yes || overwrite 2>> || yes | no || no | yes || append || | || | || &> || no | no || yes | yes || overwrite &>> || no | no || yes | yes || append || | || | || | tee || yes | yes || yes | no || overwrite | tee -a || yes | yes || yes | no || append || | || | || n.e. () || yes | yes || no | yes || overwrite n.e. () || yes | yes || no | yes || append || | || | || |& tee || yes | yes || yes | yes || overwrite |& tee -a || yes | yes || yes | yes || append List: command > output.txt

The standard output stream will be redirected to the file only, it will not be visible in the terminal. If the file already exists, it gets overwritten.

command >> output.txt

The standard output stream will be redirected to the file only, it will not be visible in the terminal. If the file already exists, the new data will get appended to the end of the file.

command 2> output.txt

The standard error stream will be redirected to the file only, it will not be visible in the terminal. If the file already exists, it gets overwritten.

command 2>> output.txt

The standard error stream will be redirected to the file only, it will not be visible in the terminal. If the file already exists, the new data will get appended to the end of the file.

command &> output.txt

Both the standard output and standard error stream will be redirected to the file only, nothing will be visible in the terminal. If the file already exists, it gets overwritten.

command &>> output.txt

Both the standard output and standard error stream will be redirected to the file only, nothing will be visible in the terminal. If the file already exists, the new data will get appended to the end of the file..

command | tee output.txt

The standard output stream will be copied to the file, it will still be visible in the terminal. If the file already exists, it gets overwritten.

command | tee -a output.txt

The standard output stream will be copied to the file, it will still be visible in the terminal. If the file already exists, the new data will get appended to the end of the file.

(*)

Bash has no shorthand syntax that allows piping only StdErr to a second command, which would be needed here in combination with tee again to complete the table. If you really need something like that, please look at "How to pipe stderr, and not stdout?" on Stack Overflow for some ways how this can be done e.g. by swapping streams or using process substitution.

command |& tee output.txt

Both the standard output and standard error streams will be copied to the file while still being visible in the terminal. If the file already exists, it gets overwritten.

command |& tee -a output.txt

Both the standard output and standard error streams will be copied to the file while still being visible in the terminal. If the file already exists, the new data will get appended to the end of the file.