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bash-redirections-cheat-sheet.txt
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bash-redirections-cheat-sheet.txt
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.---------------------------------------------------------------------------.
| |
| Bash Redirections Cheat Sheet |
| |
+---------------------------------------------------------------------------+
| |
| Created by Peteris Krumins (peter@catonmat.net) |
| www.catonmat.net -- good coders code, great coders reuse |
| |
+-----------------------------.---------------------------------------------+
| Redirection | Description |
'-----------------------------'---------------------------------------------'
| cmd > file | Redirect the standard output (stdout) of |
| | `cmd` to a file. |
+-----------------------------'---------------------------------------------'
| cmd 1> file | Same as `cmd > file`. 1 is the default file |
| | descriptor for stdout. |
+-----------------------------'---------------------------------------------'
| cmd 2> file | Redirect the standard error (stderr) of |
| | `cmd` to a file. 2 is the default file |
| | descriptor for stderr. |
+-----------------------------'---------------------------------------------'
| cmd >> file | Append stdout of `cmd` to a file. |
+-----------------------------'---------------------------------------------'
| cmd 2>> file | Append stderr of `cmd` to a file. |
+-----------------------------'---------------------------------------------'
| cmd &> file | Redirect stdout and stderr to a file. |
+-----------------------------'---------------------------------------------'
| cmd > file 2>&1 | Another way to redirect both stdout and |
| | stderr of `cmd` to a file. This *is not* |
| | same as `cmd 2>&1 > file`. |
| | Redirection order matters! |
+-----------------------------'---------------------------------------------'
| cmd > /dev/null | Discard stdout of `cmd`. |
+-----------------------------'---------------------------------------------'
| cmd 2> /dev/null | Discard stderr of `cmd`. |
+-----------------------------'---------------------------------------------'
| cmd &> /dev/null | Discard stdout and stderr. |
+-----------------------------'---------------------------------------------'
| cmd < file | Redirect the contents of the file to the |
| | stdin of `cmd`. |
+-----------------------------'---------------------------------------------'
| cmd << EOL | |
| foo | Redirect a bunch of lines to the stdin. |
| bar | If 'EOL' is quoted, text is treated |
| baz | literally. This is called a here-document. |
| EOL | |
+-----------------------------'---------------------------------------------'
| cmd <<- EOL | |
| <tab>foo | Redirect a bunch of lines to the stdin. |
| <tab><tab>bar | The <tab>'s are ignored but not the |
| EOL | whitespace. Helpful for formatting. |
+-----------------------------'---------------------------------------------'
| cmd <<< "string" | Redirect a single line of text to stdin. |
| | This is called a here-string. |
+-----------------------------'---------------------------------------------'
| exec 2> file | Redirect stderr of all commands to a file |
| | forever. |
+-----------------------------'---------------------------------------------'
| exec 3< file | Open a file for reading using a custom fd. |
+-----------------------------'---------------------------------------------'
| exec 3> file | Open a file for writing using a custom fd. |
+-----------------------------'---------------------------------------------'
| exec 3<> file | Open a file for reading and writing using |
| | a custom file descriptor. |
+-----------------------------'---------------------------------------------'
| exec 3>&- | Close a file descriptor. |
+-----------------------------'---------------------------------------------'
| exec 4>&3 | Make file descriptor 4 to be a copy of file |
| | descriptor 3. (Copy fd 3 to 4.) |
+-----------------------------'---------------------------------------------'
| exec 4>&3- | Copy file descriptor 3 to 4 and close fd 3 |
+-----------------------------'---------------------------------------------'
| echo "foo" >&3 | Write to a custom file descriptor. |
+-----------------------------'---------------------------------------------'
| cat <&3 | Read from a custom file descriptor. |
+-----------------------------'---------------------------------------------'
| (cmd1; cmd2) > file | Redirect stdout from multiple commands to a |
| | file (using a sub-shell). |
+-----------------------------'---------------------------------------------'
| { cmd1; cmd2; } > file | Redirect stdout from multiple commands to a |
| | file (faster; not using a sub-shell). |
+-----------------------------'---------------------------------------------'
| exec 3<> /dev/tcp/host/port | Open a TCP connection to host:port. |
+-----------------------------'---------------------------------------------'
| exec 3<> /dev/udp/host/port | Open a UDP connection to host:port. |
+-----------------------------'---------------------------------------------'
| cmd <(cmd1) | Redirect stdout of `cmd1` to an anonymous |
| | fifo, then pass the fifo to `cmd` as an |
| | argument. Useful when `cmd` doesn't read |
| | from stdin directly. |
+-----------------------------'---------------------------------------------'
| cmd < <(cmd1) | Redirect stdout of `cmd1` to an anonymous |
| | fifo, then redirect the fifo to stdin of |
| ____' `cmd`. Best example: |
| | diff <(find /path1 | sort) <(find /path2 | sort) |
+------------------------'----.---------------------------------------------'
| cmd <(cmd1) <(cmd2) | Redirect stdout of `cmd1` `cmd2` to two |
| | anonymous fifos, then pass both fifos as |
| | arguments to \verb|cmd|. |
+-----------------------------.---------------------------------------------'
| cmd1 >(cmd2) | Run `cmd2` with its stdin connected to an |
| | anonymous fifo, and pass the filename of |
| | the pipe as an argument to `cmd1`. |
+-----------------------------.---------------------------------------------'
| cmd1 | cmd2 | Redirect stdout of cmd1 to stdin of `cmd2`. |
| | Pro-tip: This is the same as |
| | `cmd1 > >(cmd2)`, same as `cmd2 < <(cmd1)`, |
| | same as `> >(cmd2) cmd1`, same as |
| | `< <(cmd1) cmd2`. |
+-----------------------------'---------------------------------------------'
| cmd1 |& cmd2 | Redirect stdout and stderr of `cmd1` to |
| | stdin of `cmd2` (bash 4.0+ only). |
| | Use `cmd1 2>&1 | cmd2` for older bashes. |
+-----------------------------'---------------------------------------------'
| cmd | tee file | Redirect stdout of `cmd` to a file and |
| | print it to screen. |
+-----------------------------'---------------------------------------------'
| exec {filew}> file | Open a file for writing using a named file |
| | descriptor called `{filew}` (bash 4.1+) |
+-----------------------------'---------------------------------------------'
| cmd 3>&1 1>&2 2>&3 | Swap stdout and stderr of `cmd`. |
+-----------------------------'---------------------------------------------'
| cmd > >(cmd1) 2> >(cmd2) | Send stdout of `cmd` to `cmd1` and stderr |
| | `cmd` to `cmd2`. |
+-----------------------------'---------------------------------------------'
| cmd1 | cmd2 | cmd3 | cmd4 | Find out the exit codes of all piped cmds. |
| echo ${PIPESTATUS[@]} | |
+-----------------------------'---------------------------------------------'
| |
| I explained each one of these redirections in my article All About Bash |
| Redirections: |
| |
| http://www.catonmat.net/blog/bash-one-liners-explained-part-three |
| |
+---------------------------------------------------------------------------+
| |
| Did I miss any redirections? Let me know! Email me peter@catonmat.net, or |
| fork this cheat sheet on github: |
| |
| http://www.github.com/pkrumins/bash-redirections-cheat-sheet |
| |
`-( Released under GNU Free Document License )------------------------------'