List of All Bash Redirections - Linux Cheat-Sheet

[x32x01]

List of All Bash Redirections - Linux Cheat-Sheet

Before a command is executed, its input and output may be redirected using a special notation interpreted by the shell. Redirection allows commands’ file handles to be duplicated, opened, closed, made to refer to different files, and can change the files the command reads from and writes to. Redirection may also be used to modify file handles in the current shell execution environment. The following redirection operators may precede or appear anywhere within a simple command or may follow a command. Redirections are processed in the order they appear, from left to right.

Also Read: Bash CTRL and ALT Key Shortcuts

Each redirection that may be preceded by a file descriptor number may instead be preceded by a word of the form {varname}. In this case, for each redirection operator except >&- and <&-, the shell will allocate a file descriptor greater than 10 and assign it to {varname}. If >&- or <&- is preceded by {varname}, the value of varname defines the file descriptor to close.

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 (fd) for stdout.
cmd 2> file	Redirect the standard error (stderr) of cmd to a file. 2 is the default fd 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 of cmd to a file.
cmd > file 2>&1	Another way to redirect both stdout and stderr of cmd to a file. This is not the same as cmd 2>&1 > file.
cmd > /dev/null	Discard stdout of cmd.
cmd 2> /dev/null	Discard stderr of cmd.
cmd &> /dev/null	Discard stdout and stderr of cmd.
cmd < file	Redirect the contents of the file to the standard input (stdin) of cmd.
cmd << EOL line1 line2 EOL	Redirect a bunch of lines to the stdin. If ‘EOL’ is quoted, text is treated literally. This is called a here-document.
cmd <<- EOL <tab>foo <tab>bar EOL	Redirect a bunch of lines to the stdin and strip the leading tabs.
cmd <<< “string”	Redirect a single line of text to the stdin of cmd. 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 file descriptor.
exec 3> file	Open a file for writing using a custom file descriptor.
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 file descriptor 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. (This is a bash feature, not Linux feature).
exec 3<> /dev/udp/host/port	Open a UDP connection to host: port. (This is a bash feature, not Linux feature).
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 and cmd2 to two anonymous fifos, then pass both fifos as arguments to 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)	Run cmd2 with its stdin connected to an anonymous fifo, then redirect stdout of cmd to this anonymous pipe.
cmd1 | cmd2	Redirect stdout of cmd1 to stdin of 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 of cmd to cmd2.
cmd1 | cmd2 | cmd3 | cmd4 echo ${PIPESTATUS[@]}	Find out the exit codes of all piped commands.