Sponsored Content
Top Forums Shell Programming and Scripting Confused with redirection and file descriptors Post 302316442 by AlbertGM on Friday 15th of May 2009 06:16:12 AM
Old 05-15-2009
Confused with redirection and file descriptors

Hi all,

I've been looking for the way to send stdout and stderr to different files. Well, actually I really knew how to make it, but I wanted to be sure.
I've found an instruction very interesting which I'm not able to understand:
Quote:
((/path/to/oraMon.pl 2>&1 1>&3 | tee /tmp/errors.log) 3>&1 1>&2 | tee /tmp/output.log) > /tmp/final.log 2>&1
taken from this site. It says it sends stdout to output.log, stderr to errors.log, and both to final.log.
I know 3 is another file descriptor, but which file does it refers? How does it work?
I think I understand:
  • oraMon.pl 2>&1 1>&3: stderr is redirected to stdout and stdout is redirected to 3
  • tee /tmp/errors.log 3>&1 1>&2: takes the standards output previous command, and saves it to a file. However, I don't understand why 3 is redirected to stdout, and sdout to stderr.
I still have another question. The difference between this two instructions:
Quote:
./command > mylog.log 2>&1
./command 2>&1 > mylog.log
I know first one redirects both stdout and stderr to mylog.log. The second one, I read the stderr is redirected to stdout, and stdout is redirected to a file. So I thought both should be the same, but I also read only stdout is saved to a file in the second instruction. Why?

Sorry for this large question, but I'd like to understand redirection and file descriptors.

Thanks a lot.

Albert.
 

10 More Discussions You Might Find Interesting

1. Programming

File Descriptors

Hi, I have written a daemon process, to perform certain operations in the background. For this I have to close, the open file descriptors, Does anybody know how to find out the number of open file descriptors ? Thanks in Advance, Sheetal (2 Replies)
Discussion started by: s_chordia
2 Replies

2. UNIX for Advanced & Expert Users

File Descriptors

Hello all, A few questions on file descriptors ... scenario : Sun Ultra 30 with Sun OS 5.5.1 , E250 with Solaris 2.6 In one of my servers, the file descriptor status from the soft limit and hard limits are 64 and 1024 respectively for root user. Is the soft limit (64) represents the... (3 Replies)
Discussion started by: shibz
3 Replies

3. UNIX for Dummies Questions & Answers

file descriptors

i m trying to learn processes in unix and i've been reading this but i don't quite get it. its regarding file descriptors. : each is a part of file pointers, they point to another area. indexes into an Operating system maintained table called "file descriptor table". one table per process. may... (3 Replies)
Discussion started by: a25khan
3 Replies

4. Programming

Sockets and File descriptors

I am in a Systems programming class this semester, and our current project is to write a program utilizing sockets and fork. For the project, I decided to make my own instant messaging program. I have the code completed, but I have a problem that keeps old clients from communicating with new... (3 Replies)
Discussion started by: gstlouis
3 Replies

5. UNIX for Advanced & Expert Users

File Descriptors + cron

Hi All, This thread is going to be a discussion basically bringing out more information from the experts on cron jobs and the associated file handles. So, here is the question. There is definitely a constant ' n ' as the maximum number of file handles alloted to a process ' p '. Will... (7 Replies)
Discussion started by: matrixmadhan
7 Replies

6. UNIX for Dummies Questions & Answers

how to list the files using File Descriptors

hello, I have written a script named listall.sh with the following codes init. #!/bin/bash PATH="/proj/cmon/$1" echo $PATH if ; then echo "Usage: $0 ***" exit 1 else ls -l $PATH/*.sc fi Here there are 3 subdirectories (namely - src, data and jobs)under /proj/cmon, so... (2 Replies)
Discussion started by: shyjuezy
2 Replies

7. HP-UX

exec and file descriptors

Hi, I speak and write english more or less, so I hope my asking be clear. :) In the company I am working, they are using control-m software to lunch shell scripts. So i put this command in all shell scripts: export LOGFILE_tmp=$PRODUC_DATA/tmp/${SCRIPT}_${PAIS}_`date... (0 Replies)
Discussion started by: anamcara
0 Replies

8. UNIX for Dummies Questions & Answers

Semaphores and File Descriptors

What is the difference between a file descriptor and a semaphore? My basic understanding is: - a file descriptor is a small positive integer that the system uses instead of the file name to identify an open file or socket. - a semaphore is a variable with a value that indicates the... (1 Reply)
Discussion started by: Mr_Webster
1 Replies

9. Shell Programming and Scripting

Confused with redirection

Hi Guys, First of all I am not entirely sure if this is the correct way of doing what I need to be done. I have tried to google for some suggestions and so far it got me more confused. Basically what I need is to pipe the output of a program to a function in KSH and inside the function some... (1 Reply)
Discussion started by: maddmaster
1 Replies

10. Shell Programming and Scripting

Questions about file descriptors

Hi, I'm playing with KSH I entered following command in terminal { echo "stdout" >&1; echo "stderr" >&2; } > out And I get only stoud in a new file out. My question is: Where did my stderr vanish ? (5 Replies)
Discussion started by: solaris_user
5 Replies
xfs_metadump(8) 					      System Manager's Manual						   xfs_metadump(8)

NAME
xfs_metadump - copy XFS filesystem metadata to a file SYNOPSIS
xfs_metadump [ -efgow ] [ -l logdev ] source target DESCRIPTION
xfs_metadump is a debugging tool that copies the metadata from an XFS filesystem to a file. The source argument must be the pathname of the device or file containing the XFS filesystem and the target argument specifies the destination file name. If target is -, then the output is sent to stdout. This allows the output to be redirected to another program such as a compression application. xfs_metadump should only be used to copy unmounted filesystems, read-only mounted filesystems, or frozen filesystems (see xfs_freeze(8)). Otherwise, the generated dump could be inconsistent or corrupt. xfs_metadump does not alter the source filesystem in any way. The target image is a contiguous (non-sparse) file containing all the filesystem's metadata and indexes to where the blocks were copied from. By default, xfs_metadump obfuscates most file (regular file, directory and symbolic link) names and extended attribute names to allow the dumps to be sent without revealing confidential information. Extended attribute values are zeroed and no data is copied. The only excep- tions are file or attribute names that are 4 or less characters in length. Also file names that span extents (this can only occur with the mkfs.xfs(8) options where -n size > -b size) are not obfuscated. Names between 5 and 8 characters in length inclusively are partially obfuscated. xfs_metadump should not be used for any purposes other than for debugging and reporting filesystem problems. The most common usage scenario for this tool is when xfs_repair(8) fails to repair a filesystem and a metadump image can be sent for analysis. The file generated by xfs_metadump can be restored to filesystem image (minus the data) using the xfs_mdrestore(8) tool. OPTIONS
-e Stops the dump on a read error. Normally, it will ignore read errors and copy all the metadata that is accessible. -f Specifies that the filesystem image to be processed is stored in a regular file (see the mkfs.xfs -d file option). This can also happen if an image copy of a filesystem has been made into an ordinary file with xfs_copy(8). -g Shows dump progress. This is sent to stdout if the target is a file or to stderr if the target is stdout. -l logdev For filesystems which use an external log, this specifies the device where the external log resides. The external log is not copied, only internal logs are copied. -o Disables obfuscation of file names and extended attributes. -w Prints warnings of inconsistent metadata encountered to stderr. Bad metadata is still copied. DIAGNOSTICS
xfs_metadump returns an exit code of 0 if all readable metadata is successfully copied or 1 if a write error occurs or a read error occurs and the -e option used. NOTES
As xfs_metadump copies metadata only, it does not matter if the source filesystem has a realtime section or not. If the filesystem has an external log, it is not copied. Internal logs are copied and any outstanding log transactions are not obfuscated if they contain names. xfs_metadump is a shell wrapper around the xfs_db(8) metadump command. SEE ALSO
xfs_repair(8), xfs_mdrestore(8), xfs_freeze(8), xfs_db(8), xfs_copy(8), xfs(5) BUGS
Email bug reports to xfs@oss.sgi.com. xfs_metadump(8)
All times are GMT -4. The time now is 02:36 PM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy