Перенаправление потока ввода/вывода

Смотря где. Наверное, вам нужно ″man bash″. Насчёт стрелки влево я не понял, «меньше» или «больше» или что?

Да, это bash Три стрелки влево (меньше)

Это here-string, как бы однострочный here-doc, в то, что справа от трёх «меньше» выполняются различные подстановки (скобки, замена тильды, переменные среды и т.д.) и результат этого передаётся на stdin команды, стоящей слева от этих трёх символов.

Насчёт стрелки влево я не понял

mplayer "http://radio-tochka.com:4570" |& while read -r line;  do if grep "ICY" <<< "$line" &> /dev/null; then iconv -f cp1251 <<< "$line"; else echo "$line"; fi; done

а что выполняют остальные?

Если речь про bash, то:

https://www.gnu.org/software/bash/manual/html_node/Redirections.html

https://catonmat.net/ftp/bash-redirections-cheat-sheet.pdf

3.6.1 Redirecting Input

Redirection of input causes the file whose name results from the expansion of word to be opened for reading on file descriptor n, or the standard input (file descriptor 0) if n is not specified.

The general format for redirecting input is:

[n]<word 3.6.2 Redirecting Output

Redirection of output causes the file whose name results from the expansion of word to be opened for writing on file descriptor n, or the standard output (file descriptor 1) if n is not specified. If the file does not exist it is created; if it does exist it is truncated to zero size.

The general format for redirecting output is:

[n]>[|]word If the redirection operator is ‘>’, and the noclobber option to the set builtin has been enabled, the redirection will fail if the file whose name results from the expansion of word exists and is a regular file. If the redirection operator is ‘>|’, or the redirection operator is ‘>’ and the noclobber option is not enabled, the redirection is attempted even if the file named by word exists.

3.6.3 Appending Redirected Output

Redirection of output in this fashion causes the file whose name results from the expansion of word to be opened for appending on file descriptor n, or the standard output (file descriptor 1) if n is not specified. If the file does not exist it is created.

The general format for appending output is:

[n]>>word 3.6.4 Redirecting Standard Output and Standard Error

This construct allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be redirected to the file whose name is the expansion of word.

There are two formats for redirecting standard output and standard error:

&>word and

&word Of the two forms, the first is preferred. This is semantically equivalent to

word 2>&1 When using the second form, word may not expand to a number or ‘-’. If it does, other redirection operators apply (see Duplicating File Descriptors below) for compatibility reasons.

3.6.5 Appending Standard Output and Standard Error

This construct allows both the standard output (file descriptor 1) and the standard error output (file descriptor 2) to be appended to the file whose name is the expansion of word.

The format for appending standard output and standard error is:

&>>word This is semantically equivalent to

word 2>&1 (see Duplicating File Descriptors below).

3.6.6 Here Documents

This type of redirection instructs the shell to read input from the current source until a line containing only word (with no trailing blanks) is seen. All of the lines read up to that point are then used as the standard input (or file descriptor n if n is specified) for a command.

The format of here-documents is:

[n]<<[-]word here-document delimiter No parameter and variable expansion, command substitution, arithmetic expansion, or filename expansion is performed on word. If any part of word is quoted, the delimiter is the result of quote removal on word, and the lines in the here-document are not expanded. If word is unquoted, all lines of the here-document are subjected to parameter expansion, command substitution, and arithmetic expansion, the character sequence \newline is ignored, and ‘\’ must be used to quote the characters ‘\’, ‘$’, and ‘`’.

If the redirection operator is ‘<<-’, then all leading tab characters are stripped from input lines and the line containing delimiter. This allows here-documents within shell scripts to be indented in a natural fashion.

3.6.7 Here Strings

A variant of here documents, the format is:

[n]<<< word The word undergoes brace expansion, tilde expansion, parameter and variable expansion, command substitution, arithmetic expansion, and quote removal. Pathname expansion and word splitting are not performed. The result is supplied as a single string, with a newline appended, to the command on its standard input (or file descriptor n if n is specified).

3.6.8 Duplicating File Descriptors

The redirection operator

[n]<&word is used to duplicate input file descriptors. If word expands to one or more digits, the file descriptor denoted by n is made to be a copy of that file descriptor. If the digits in word do not specify a file descriptor open for input, a redirection error occurs. If word evaluates to ‘-’, file descriptor n is closed. If n is not specified, the standard input (file descriptor 0) is used.

The operator

[n]>&word is used similarly to duplicate output file descriptors. If n is not specified, the standard output (file descriptor 1) is used. If the digits in word do not specify a file descriptor open for output, a redirection error occurs. If word evaluates to ‘-’, file descriptor n is closed. As a special case, if n is omitted, and word does not expand to one or more digits or ‘-’, the standard output and standard error are redirected as described previously.

3.6.9 Moving File Descriptors

The redirection operator

[n]<&digit- moves the file descriptor digit to file descriptor n, or the standard input (file descriptor 0) if n is not specified. digit is closed after being duplicated to n.

Similarly, the redirection operator

[n]>&digit- moves the file descriptor digit to file descriptor n, or the standard output (file descriptor 1) if n is not specified.

3.6.10 Opening File Descriptors for Reading and Writing

The redirection operator

[n]<>word causes the file whose name is the expansion of word to be opened for both reading and writing on file descriptor n, or on file descriptor 0 if n is not specified. If the file does not exist, it is created.