io redirection is the process of changing where the output and input of a program originate

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-1
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2answers
469 views

Copying a few lines from stdout to stderr - but only if stderr is different from stdout

I have a bash script "backup.sh", which prints out everything to stdout, including all the files that are transferred during backup. I'd like to make it possible to keep that full output, but when ...
6
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2answers
1k views

redirection and pipeline

I was wondering about differences and relation between redirection and pipeline. Is pipeline only used to connect stdout output of a command to stdin input of another command? Is redirection only ...
6
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2answers
184 views

understand a sequence of redirections

If several redirections are used together, does changing their order make difference? How shall one understand the meaning of their order? Is the chained channel of redirections built as reading the ...
4
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4answers
171 views

Make mistakenly thinks rule succeeded because of 0-sized file generated by output redirect

In a makefile, I have several rules that look like this: out.txt: foo.sh input.txt ./foo.sh -i input.txt > out.txt If foo.sh fails, then out.txt will be created as a 0-sized file. If I run ...
21
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2answers
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How can I assign the output of a command to a shell variable?

I want to assign the result of an expression to a variable and concatenate it with a string, then echo it. Here's what I've got: #!/bin/bash cd ~/Desktop; thefile= ls -t -U | grep -m 1 "Screen Shot"; ...
6
votes
2answers
6k views

Howto create a permanent client connection with netcat?

I'm writing a bash script that constantly read a folder in a loop to send data to a server at a defined time interval. I'm using netcat as the tool to connect to the server and send the data. My ...
8
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6answers
1k views

IO redirection and the head command

I was trying to quickly edit an .hgignore file from the Cygwin bash shell today, and I added a line that was a mistake. I'm not sure if this was the best way to do it, but I quickly thought of using ...
9
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2answers
9k views

See the STDOUT redirect of a running process

If I start an app with this command: /path/to/my/command >> /var/log/command.log And the command doesn't return, is there a way, from another prompt, to see what the STDOUT redirect is set ...
7
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2answers
1k views

How to detect if input is from argument, file or terminal

In bash, is there a way to know if a given script has been invoked with: $ myscript.sh myfile or: $ myscript.sh < myfile Inside some scripts I always have accessed the contents of myfile with ...
19
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5answers
18k views

view stdout for another pts [duplicate]

Here is the situation. I left my pc at home doing an rsync from a 2TB hard drive to another 2TB hard drive (it's going to take a while since they are both USB 2.0). I am now at work and I have ssh-ed ...
4
votes
3answers
601 views

script to use the output of a command (ls) and use it in another command

I have a collection of pdf files I would like to convert to epub. I know Calibre's command ebook-convert will do the trick (nicely might I add). However I have more than one file. I'd like to be able ...
1
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1answer
382 views

Which process/program create/write the file which I/O is redirected to?

When learning SELinux, I executed semanage fcontext -l > fcontext.txt under /root directory to dump massive fcontext information to a file. The funny result is: fcontext.txt was created, but the ...
7
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2answers
2k views

Precedence of stdin and stdout redirection in Bash

My question is about redirection precedence is bash. Suppose you have a command: cmd1 < cmd2 > cmd3 Would it translate to: (cmd1 < cmd2) > cmd3 Or cmd1 < (cmd2 > cmd3)
14
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1answer
20k views

File descriptors & shell scripting

I am having a very hard time understanding how does one use file descriptors in shell scripts. I know the basics such as exec 5 > /tmp/foo So fd 5 is attached to foo for writing. exec 6 < ...
0
votes
1answer
4k views

Unix > overwrite command?

I'm doing a shell command (such as sh run.sh > log.txt). How do you overwrite the file each time (so each time I run it log.txt doesn't get appended) I'm doing this in a python script and I'm ...
10
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2answers
3k views

Use HERE file and redirect output of command

I have the following code in a batch script: mpirun -np 6 ./laplace <<END 100 100 100 0.01 100 3 2 1 END | tail -n 1 > output But it isn't working. What I want it to do is to use the HERE ...
5
votes
2answers
10k views

Output progess of the scp/sftp command to both standard out and a file on linux server

I am writing a release script, which uses scp/sftp to get the the file from a remote server, we want to log the output of this script to a release.log file as well. I am using "tee" to achieve this, ...
1
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2answers
1k views

writing a command transcript to file

Here is a script from Mercurial issue 2743. Call it mq.sh. I'm trying to get it to do the following things, on Debian squeeze. Echo commands + standard output + standard error to a file. Prefix with ...
3
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1answer
2k views

using system command in awk script

In an AWK script I am using a command system(date) to print the current date in a file but after this command is executed next line is also added implicitly. Is there any way in AWK to print ...
8
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3answers
5k views

How do i open all files that are the result of a ls command?

I'd like to open all text files that are the result of a ls command using a text editor. How do i do this?
16
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2answers
7k views

How to diff a file and output from the command?

Normally you would write: diff file1 file2 But I would like to diff a file and output from the command (here I make command a trivial one): diff file1 <(cat file2 | sort) Ok, this work when I ...
36
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5answers
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How can I make iconv replace the input file with the converted output?

I have a bash script which enumerates through every *.php file in a directory and applies iconv to it. This gets output in STDOUT. Since adding the -o parameter ( in my experience ) actually writes ...
17
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5answers
19k views

Show only stderr on screen but write both stdout and stderr to file

How can I use BASH magic to achieve this? I want to only see stderr output on the screen, but I want both stdout and stderr to be written to a file. Clarification: I want both stdout and stderr to ...
44
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5answers
20k views

How can I create a /dev/null-like “blackhole” directory?

I would like to create a "/dev/null" directory (or a "blackhole" directory) such that any files written to it are not really written, but just disappear. I have an application that writes out large ...
39
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11answers
22k views

How do I reuse the last output from the command line?

This is a noob question, but I'd like to know how to reuse the last output from the console, ie: pv-3:method Xavier$ python -c "from distutils.sysconfig import get_python_lib; print get_python_lib()" ...
1
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1answer
828 views

Splitting stdin to different outputs in bash [duplicate]

Possible Duplicate: Is there a way in bash to redirect output and still have it go to stdout? How would I send /dev/stdin to both /dev/stdout and a $logfile in one command? One solution ...
6
votes
3answers
6k views

Write to a file without redirection?

I am writing a regular compiled application that needs to create a special file and write a magic cookie into it. I can’t write the file directly from the application, the system security model ...
6
votes
3answers
7k views

Pass xargs argument as a string to another command with '>'?

Suppose I have a bunch of files in /tmp/. I do find . -type f | xargs -iFILES And I want to do a md5sum in each file, outputting to a file with the same name, but with .md5 extension. find . ...
20
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4answers
10k views

How to redirect stderr,out to different files and also display in terminal?

To make it clear, I want to see the output of a command in the terminal as if there were no redirection. Also stderr need to be redirected to err.log and stdout need to be redirected to stdout.log. ...
8
votes
2answers
4k views

Iterate over the output of a command in bash without a subshell

I want to loop over the output of a command without creating a sub-shell or using a temporary file. The initial version of of my script looked like this, but this doesn't work since it creates a ...
10
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4answers
4k views

Can I make `cut` change a file in place?

The man page doesn't give me much hope, but I'm hoping it's an undocumented (and/or GNU-specific) feature.
4
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3answers
2k views

How do I use redirection with sudo [duplicate]

Possible Duplicate: Redirecting stdout to a file you don't have write permission on Yeah I could (and probably will) just escalate to root, but I'd like to know why this doesn't work? ...
3
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2answers
8k views

How to insert text into a root-owned file using sudo? [duplicate]

Possible Duplicate: Redirecting stdout to a file you don't have write permission on Running a command like sudo echo 'text' >> /file.txt fails with: bash: /file.txt: Permission ...
21
votes
1answer
2k views

Is there a way in bash to redirect output and still have it go to stdout?

Okay. If I wanted to redirect the output of a program to a file, I'd do something like this prog > file If I wanted to redirect both stdout and stderr to that file, then I'd do prog > file ...
9
votes
1answer
1k views

How do I redirect output to cd?

Is it possible to redirect a command's output to cd? For example, I searched for a directory using locate and got the path to it. Now, instead of writing a cd path, can I redirect the locate output to ...
3
votes
4answers
361 views

Is there a way to redirect a file that is written

I have an application which I can not change, that writes to a big 250 GB plain text file. After compressing with GZ it is only 30 GB. This application has no option of compressing it's output, and ...
42
votes
7answers
33k views

How to grep standard error stream (stderr)?

I am using ffmpeg to get the meta info of an audio clip. But I am unable to grep it. $ ffmpeg -i 01-Daemon.mp3 |grep -i Duration FFmpeg version SVN-r15261, Copyright (c) 2000-2008 Fabrice ...
5
votes
2answers
876 views

RS232 chat. Simplest way?

I'm working in a project in which I will have to deal with serial communications. For testing, I want make to 2 computers speak to each other (with my interaction) via RS232. Will the next thing ...
56
votes
4answers
36k views

How to redirect output of wget as input to unzip?

I have to download a file from this link. The file download is a zip file which I will have to unzip in the current folder. Normally, I would download it first, then run the unzip command. $ wget ...
2
votes
1answer
464 views

How can I suppress unneeded output from emacsclient?

I use emacs fairly regularly and am trying to configure my system to use emacsclient when possible. To do this I have done the following: In .bashrc: EDITOR='emacsclient -ca emacs' ...
8
votes
3answers
9k views

Redirect stdout over ssh

I would like to run something > file on a remote system through ssh, but if I run ssh host something > file the redirection is executed locally as ssh etc > file I've tried it with ' ...
17
votes
3answers
3k views

How to redirect output of a running program to /dev/null

I know that in order to suppress the output of a program I can redirect it to /dev/null, for example to hide all error and warning messages from chromium I can start the program like this ...
70
votes
5answers
7k views

Redirecting stdout to a file you don't have write permission on

When you attempt to modify a file without having write permissions on it, you get an error: > touch /tmp/foo && sudo chown root /tmp/foo > echo test > /tmp/foo zsh: permission ...
14
votes
5answers
2k views

Using text from previous commands' output

EDIT April, 2015: If you have this same question I recommend also checking http://xiki.org/ I know this is not how terminals work, but I find myself often wishing there was an easy way of using ...