Sponsored Content
Top Forums UNIX for Dummies Questions & Answers tee vs output redirection confusion Post 302299836 by Perderabo on Saturday 21st of March 2009 04:36:03 PM
Old 03-21-2009
Quote:
Originally Posted by c_d
I wish to know whats going on here.
what actually do the makers of unix mean when they say redirection and what they mean when they say duplication?
Redirection is changing which file a program uses to read or write. Duplication, as used in the context of the tee program, means reading some input and writing that input several times to (we presume) different files.

Quote:
Originally Posted by radoulov
Code:
{ rm f1&&cat - f2|sort -u>f1;}<f1

Smilie Twisted but brilliant. I'm not sure if I love it or hate it... but that's a hallmark of great art.

To clarify: when you do:
somecommand > file
the shell forks a copy of itself to run the command. This copy opens "file" for writing, truncating it to empty if it already exists. Then the copy exec's "somecommand". By the time somecommand starts to run, the output file is already empty.
 

10 More Discussions You Might Find Interesting

1. Shell Programming and Scripting

log script input and output using tee ?

hi, new to to forum... i've been trying to create a script in tcsh but i'm having a problem with one thing... the script has to keep log of it's input and output so i'm using tee -a log | script | tee -a log this keeps the logs as asked, but it gives me an extra empty prompt (not in the... (0 Replies)
Discussion started by: moseschrist
0 Replies

2. Shell Programming and Scripting

Duplicate output without tee

Hi, Is there anyway to duplicate output without using tee? Let me explain the problem. We are use ssh to login to remote server and save output to a file using tee commands for auditing purposes. When we use vi editor in ssh session, letters get garbled and cant really use vi. Without tee it... (7 Replies)
Discussion started by: eagles1
7 Replies

3. Shell Programming and Scripting

How Unix tee to send pipeline output to 2 pipes ?

Hi, I would like to process, filter the same ASCII asynchronous live data stream in more than one pipe pipeline. So the one pipeline should filter out some records using grep key word and more than one pipes pipelines each should grep for another key words, each set seperately for each... (5 Replies)
Discussion started by: jack2
5 Replies

4. Shell Programming and Scripting

redirection and output

I'm redirecting the output of a command to a logfile, however, if the user is on a terminal I would also like the output to be displayed on the screen. tar tvf some_tarfile >Logfile if the user is on a term then have the output to the Logfile and also be displayed on the screen at the same... (2 Replies)
Discussion started by: nck
2 Replies

5. Shell Programming and Scripting

Redirection output

Hi there I have a script that runs but it outputs everything onto the screen instead of a file. I've tried using the > outputfile.txt however all it does is dump the output to the screen and creates an outputfile.txt but doesn't put anything in that file. Any help would be appreciated ... (6 Replies)
Discussion started by: kma07
6 Replies

6. Shell Programming and Scripting

problem with suppressed output to file using echo and tee command

Hi, When I run the following command in terminal it works. The string TEST is appended to a file silently. echo TEST | tee -a file.txt &>/dev/null However, when I paste this same line to a file, say shell1.sh, and use bourne shell . I run this file in terminal, ./shell1.sh. However I... (1 Reply)
Discussion started by: shahanali
1 Replies

7. Shell Programming and Scripting

Output redirection

We have an application here that does some table queries and then prints the result on screen. I do not have the code of this application (which i will just call "queryCommand"), but what it does is that you call it with some parameters and it prints some info about the query and then the... (5 Replies)
Discussion started by: jolateh
5 Replies

8. UNIX for Dummies Questions & Answers

Output redirection

Hello i am trying to write a script that will redirect the output to a certain file. Here is the code so far: #!/bin/bash ps -e | sort | more > psfile When I execute the script nothing happens since i assume the output was redirected to the file called psfile. When I try to look at the... (1 Reply)
Discussion started by: mfruiz34
1 Replies

9. Shell Programming and Scripting

Redirection of ls -l output

Hi I am making a script where i want to redirect the output of ls -l to a file Example #ls -l fil1.txt > /opt/temp/a.txt ac: No such file or directory I want to capture output of this command like here output is ac: No such file or directory can anyone help (4 Replies)
Discussion started by: anish19
4 Replies

10. Shell Programming and Scripting

output redirection

Hi all I was wondering if there was a slicker way of doing this without the file - awk '{print $2}' FS=":" "${FILE}" > "${TMPFILE}" { read M_GRP_ID || m_fail 1 "Error: Read failed 1 (${FUNCNAME})" read M_GRP_WAIT || m_fail 1 "Error: Read failed 2 (${FUNCNAME})" }... (6 Replies)
Discussion started by: steadyonabix
6 Replies
tee(1)							      General Commands Manual							    tee(1)

NAME
tee - Displays the output of a program and copies it into a file SYNOPSIS
tee [-ai] file... STANDARDS
Interfaces documented on this reference page conform to industry standards as follows: tee: XCU5.0 Refer to the standards(5) reference page for more information about industry standards and associated tags. OPTIONS
Adds the output to the end of file instead of writing over it. Ignores the SIGINT signal. OPERANDS
Standard input is stored into, or appended to, the file specified. [Tru64 UNIX] The tee command can accept up to 20 file arguments. DESCRIPTION
The tee command reads standard input and writes to both standard output, and each specified file. The tee command is useful when you wish to view program output as it is displayed, and also want to save it in a file. The tee command does not buffer output, so you may wish to pipe the output of tee to more if more than one full screen of data is anticipated. NOTES
If a write to any file fails, the exit status of tee will be non-zero. Writes to all other specified files may be successful, and opera- tion will continue until standard input is exhausted. EXIT STATUS
The following exit values are returned: Successful completion. An error occurred. EXAMPLES
To view and save the output from a command at the same time, enter: lint program.c | tee program.lint This displays the standard output of the command lint program.c at the terminal, and at the same time saves a copy of it in the file program.lint. If program.lint already exists, it is deleted and replaced. To display and append to a file, enter: lint program.c | tee -a program.lint This displays the standard output of lint program.c at the terminal and at the same time appends a copy of it to the end of pro- gram.lint. If the file program.lint does not exist, it is created. ENVIRONMENT VARIABLES
The following environment variables affect the execution of tee: Provides a default value for the internationalization variables that are unset or null. If LANG is unset or null, the corresponding value from the default locale is used. If any of the internationalization vari- ables contain an invalid setting, the utility behaves as if none of the variables had been defined. If set to a non-empty string value, overrides the values of all the other internationalization variables. Determines the locale for the interpretation of sequences of bytes of text data as characters (for example, single-byte as opposed to multibyte characters in arguments). Determines the locale for the for- mat and contents of diagnostic messages written to standard error. Determines the location of message catalogues for the processing of LC_MESSAGES. SEE ALSO
Commands: cat(1), echo(1), script(1) Standards: standards(5) tee(1)
All times are GMT -4. The time now is 12:32 PM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy