bash 리다이렉션(redirection)

리다이렉션은, 데이터의 흐름(?)을 다른 곳으로 돌려주는 것을 의미한다.

일반적으로
fd = 0 은 stdin(입력)
fd = 1 은 stdout(표준출력)
fd = 2 는 stderr(표준에러출력)
으로 설정되는데, 이러한 출력을 다른 곳으로 돌려주는 역활을 한다.

예를들어,
에러만 파일에 저장하려면
make 2> err.log

일반메시지만 저장하려면
make > err.log

둘다 저장하려면
make > err.log 2>&1

으로 하면된다.

make 2>&1 err.log
라고 하면 에러가나니, 반드시 파일명과 함께 리다이렉션시킬 방향을 별도로 적어 주어야 한다.

REDIRECTION        Before  a command is executed, its input and output may be redirected using a special notation interpreted by the        shell.  Redirection may also be used to open and close files for 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.        In the following descriptions, if the file descriptor number is omitted, and the first character of the  redirec-        tion  operator is <, the redirection refers to the standard input (file descriptor 0).  If the first character of        the redirection operator is >, the redirection refers to the standard output (file descriptor 1).        The word following the redirection operator in the following descriptions, unless otherwise noted,  is  subjected        to  brace  expansion,  tilde  expansion,  parameter  expansion, command substitution, arithmetic expansion, quote        removal, pathname expansion, and word splitting.  If it expands to more than one word, bash reports an error.        Note that the order of redirections is significant.  For example, the command               ls > dirlist 2>&1        directs both standard output and standard error to the file dirlist, while the command               ls 2>&1 > dirlist        directs only the standard output to file dirlist, because the standard error was duplicated  as  standard  output        before the standard output was redirected to dirlist. [링크 : http://linux.die.net/man/1/bash]