Bash Redirections Cheat Sheet
.---------------------------------------------------------------------------. | | | Bash Redirections Cheat Sheet | | | +---------------------------------------------------------------------v1.08-+ | | | Created by Peter Krumins (peter@catonmat.net, @pkrumins on twitter) | | 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: | | | | www.catonmat.net/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: | | | | www.github.com/pkrumins/bash-redirections-cheat-sheet | | | `-( Released under GNU Free Document License )------------------------------'
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