'redirection'에 해당되는 글 1건

  1. 2009.10.20 Shell Redirection

Shell Redirection

ITWeb/개발일반 2009.10.20 14:20
man bash 하신 후 redirection 부분 참고 하시면 됩니다.

Handle Name Description
0 stdin Standard input
1 stdout Standard output
2 stderr Standard error

아래는 뽑아서 올려 놓은 거랍니다.. :)

REDIRECTION
       Before  a command is executed, its input and output may be redirected using a special notation inter-
       preted by the shell.  Redirection may also be used to open and close files for the current shell exe-
       cution environment.  The following redirection operators may precede or appear anywhere within a sim-
       ple 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 redirection 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 stan-
       dard output before the standard output was redirected to dirlist.

       Bash handles several filenames specially when they are used in redirections, as described in the fol-
       lowing table:

              /dev/fd/fd
                     If fd is a valid integer, file descriptor fd is duplicated.
              /dev/stdin
                     File descriptor 0 is duplicated.
              /dev/stdout
                     File descriptor 1 is duplicated.
              /dev/stderr
                     File descriptor 2 is duplicated.
              /dev/tcp/host/port
                     If  host is a valid hostname or Internet address, and port is an integer port number or
                     service name, bash attempts to open a TCP connection to the corresponding socket.
              /dev/udp/host/port
                     If host is a valid hostname or Internet address, and port is an integer port number  or
                     service name, bash attempts to open a UDP connection to the corresponding socket.

       A failure to open or create a file causes the redirection to fail.

       Redirections  using  file  descriptors  greater than 9 should be used with care, as they may conflict
       with file descriptors the shell uses internally.

   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

   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 regu-
       lar  file.   If  the  redirection  operator is >|, or the redirection operator is > and the noclobber
       option to the set builtin command is not enabled, the redirection is attempted even if the file named
       by word exists.

   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

   Redirecting Standard Output and Standard Error
       Bash allows both the standard output (file descriptor 1) and the standard error output (file descrip-
       tor 2) to be redirected to the file whose name is the expansion of word with this construct.

       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

   Here Documents
       This type of redirection instructs the shell to read input from the current source until a line  con-
       taining only word (with no trailing blanks) is seen.  All of the lines read up to that point are then
       used as the standard input for a command.

       The format of here-documents is:

              <<[-]word
                      here-document
              delimiter

       No parameter expansion, command substitution, arithmetic expansion, or  pathname  expansion  is  per-
       formed  on  word.  If any characters in word are 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.
       In the latter case, 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.

   Here Strings
       A variant of here documents, the format is:

              <<<word

       The word is expanded and supplied to the command on its standard input.

   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.  As a special case, if n is omitted, and word does not expand to  one  or
       more digits, the standard output and standard error are redirected as described previously.

   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.

   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  cre-
       ated.

신고
Trackback 0 : Comment 0