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Full Discussion: Redirecting STDERR to file and screen, STDOUT only to file
Top Forums Shell Programming and Scripting Redirecting STDERR to file and screen, STDOUT only to file Post 302697711 by alister on Friday 7th of September 2012 09:06:58 AM
Old 09-07-2012
The y-shaped hose and bucket analogy paints a memorable image. Nicely done. The only thing I'd add, explicitly (it's implied in your explanation), is that pipe redirection occurs before other, left-to-right redirections.

Quote:
Originally Posted by bakunin
The only uncertainty left is that i am not sure if the exact sequence of the messages will be preserved...
Even without the pipe and redirections, you can't depend on your average script/executable to emit messages in the exact order that they're generated, since typically a mix of unbuffered (stderr) and buffered (stdout) streams are used.

Of much greater importance is that script 2>&1 1>/some/file | tee -a /some/file involves multiple processes writing to the same file without any form of communication. Writes from script will clobber writes from tee, or vice versa. If they at least shared a file descriptor, while one message could still split another in two, there would never be any overwriting.

Regards,
Alister
Last edited by alister; 09-07-2012 at 10:47 AM..
This User Gave Thanks to alister For This Post:
bakunin
 

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LEARN ABOUT OPENSOLARIS

tee

tee(1)								   User Commands							    tee(1)

NAME

       tee - replicate the standard output

SYNOPSIS

   /usr/bin/tee
       /usr/bin/tee [-ai] [file]...

   ksh93
       tee [-ail] [file]...

DESCRIPTION

   /usr/bin/tee
       /usr/bin/tee  copies  standard  input  to standard output, making a copy in zero or more files. tee does not buffer its output. The options
       determine if the specified files are overwritten or appended to.

   ksh93
       The tee built-in in ksh93 is associated with the /bin and /usr/bin paths. It is invoked when tee is executed without a pathname prefix  and
       the pathname search finds a /bin/tee or /usr/bin/tee executable.

       tee  copies  standard input to standard output and to zero or more files. The options determine whether the specified files are overwritten
       or appended to. The tee utility does not buffer output. If a write to a file fails, tee continues to write to other files although it exits
       with a non-zero exit status.

       The number of file operands that can be specified is limited by the underlying operating system.

OPTIONS

   /usr/bin/tee
       The following options are supported by /usr/bin/tee:

       -a    Appends the output to the files rather than overwriting them.

       -i    Ignores interrupts.

   ksh93
       The following options are supported by the tee built-in command in ksh93:

       -a		      Appends the output to the files rather than overwriting them.
       --append

       -i		      Ignores SIGINT signal.
       --ignore-interrupts

       -l		      Sets the standard output to be line buffered.
       --line-buffer

OPERANDS

       The following operands are supported:

       file    A path name of an output file. Processing of at least 13 file operands are supported.

USAGE

       See largefile(5) for the description of the behavior of tee when encountering files greater than or equal to 2 Gbyte ( 2^31 bytes).

ENVIRONMENT VARIABLES

       See  environ(5)	for  descriptions of the following environment variables that affect the execution of tee: LANG, LC_ALL, LC_CTYPE, LC_MES-
       SAGES, and NLSPATH.

EXIT STATUS

   /usr/bin/tee
       The following exit values are returned by /usr/bin/tee:

       0     The standard input was successfully copied to all output files.

       >0    The number of files that could not be opened or whose status could not be obtained.

   ksh93
       The following exit values are returned by tee in ksh93:

       0     Successful completion.

       >0    An error occurred.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

   /usr/bin/tee
       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+
       |CSI			     |Enabled			   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Committed 		   |
       +-----------------------------+-----------------------------+
       |Standard		     |See standards(5). 	   |
       +-----------------------------+-----------------------------+

   ksh93
       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |See below.		   |
       +-----------------------------+-----------------------------+

       The ksh93 built-in binding to /bin and /usr/bin is Volatile. The built-in interfaces are Uncommitted.

SEE ALSO

       cat(1), ksh93(1), attributes(5), environ(5), largefile(5), standards(5)

SunOS 5.11							    20 Nov 2007 							    tee(1)
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