Chains the standard streams of a series of commands

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8
votes
2answers
1k views

Is it possible to make seek() operations on a named pipe return successful?

Is there any way to make it so that when programs try to perform seek() operations on a named pipe it will come back successful (but act as if the pipe was an empty file) instead of 'Illegal seek'? I ...
16
votes
10answers
19k views

What's a good example of piping commands together?

If you were helping someone to learn the concept of pipes on the command line what example would you use? The example that actually came up was as follows: cat whatever.txt | less I feel like ...
2
votes
2answers
1k views

How can I retain the console input in mplayer when reading from stdin?

I'm playing around with the command line interface of mplayer. I'd like to script it in the following way find /some/path/ -type f | grep -vif blacklist | mplayer -shuffle -playlist - where ...
22
votes
4answers
1k views

Are Linux utilities smart when running piped commands?

I was just running a few commands in a terminal and I started wondering, does Unix/Linux take shortcuts when running piped commands? For example, let's say I have a file with one million lines, the ...
14
votes
5answers
6k views

Shell Script mktemp, what's the best method to create temporary named pipe?

I'm aware its best to create temporary files with mktemp, but what about named pipes? I have an idea, I'm sure it would work, but I would really like an expert opinion. I prefer things to be as ...
3
votes
1answer
605 views

ssh “-f” don't give back hand in bash when listening to stdout/stderr

Please look at these: ## Does NOT return to the shell, but Ctrl-C can exit ssh -S none -fNR 13018:localhost:22 example.com | cat ## Returns to the shell (no "-S none") ssh -fNR ...
4
votes
1answer
272 views

Why did using xargs fail in this case?

I tried to understand the usage of xargs and did the following experiment. ls | xargs | touch I want to refresh the files dates and directoris in the curent directory. Though it is a bit silly,for ...
1
vote
1answer
282 views

How to know if a Linux command can read from STDIN?

I noticed this problem when I became confused with pipe, one command send its executing output to the STDOUT, which is the STDIN for the other command, which can read from STDIN. How do I know if a ...
11
votes
4answers
3k views

Follow a pipe using less?

Can less follow (by pressing F) a piped input (similarly to a file)? For a file that is being written to, the command less <file> will follow the file when pressing F. But if I have a ...
10
votes
1answer
2k views

Readable comments on separate lines in a multi-line bash command with pipelines?

When creating shell scripts using pipelines, and using the backslash to continue lines, I want to insert comments on separate lines, in a robust, readable and portable fashion. For example, given ...
2
votes
1answer
4k views

How to set a new password from bash?

I'm using busybox with a limited passwd (I don't have --stdin option) and without chpasswd and I need to change the password of an user from bash. Here is my best result: echo newpassword > ...
2
votes
2answers
2k views

Passing values through pipes

I don't quite understand pipes in Linux command line. I noticed that: ll - R | grep *.pdf will list files ending with .pdf But locate *.pdf | du -h will not calculate the size of files ...
11
votes
3answers
3k views

How can I pipe output to another process, but retain the error state of the first process? [duplicate]

Possible Duplicate: Get exit code of process that's piped to another I am using the following command line (in a makefile) to pipe the verbose error messages from my compiler through a ...
3
votes
2answers
2k views

How can I pipe input from one SSH session to another? Using fifo?

A while ago I saw an article about piping messages from one console window to another using fifo ? I haven't used that before and can't find my link to the article. How can I set this up? I'd like ...
8
votes
3answers
3k views

Piping STDERR vs. STDOUT

According to "Linux: The Complete Reference 6th Edition" (pg. 44), you can pipe only STDERR using the |& redirection symbols. I've written a pretty simple script to test this: #!/bin/bash echo ...
2
votes
2answers
2k views

I need to transfer a very large folder over FTP, without creating a file first

I am running an Amazon EC2 instance that is limited in disk space. I have a very large folder that I need to FTP to my local machine, preferably without creating an intermediate tar file, since there ...
12
votes
3answers
7k views

Non-blocking buffered named pipe?

I'm looking for something I suspect doesn't exist: A non-blocking buffered named pipe (fifo) for use from the command line. Is there such a thing? Here's the use case: Suppose I have a process that's ...
1
vote
2answers
352 views

Burning a directory structure from a stdin pipe

I'm trying to do something tricky, I want to burn a directory structure onto a CD from a pipe stream. The reason is that it is coming from the network and I don't want it written on the hard drive of ...
5
votes
1answer
630 views

Pipes vs process substitution

While trying the cat "$@" trick to read from either standard input or given files, it turned out that pipe and process substitution handle a missing trailing newline differently: printf %s foo > ...
2
votes
4answers
2k views

Open file found with 'find' command

This is probably an easy one, but I can't figure it out and it's pretty much not searchable. In a folder hierarchy I have exactly one file of type xyz. I want to find that file and open it with a ...
4
votes
3answers
2k views

Create a temporary file from a stdout redirect or pipe

Some commands only output to stdout. Some tools only work on files. Is there a command that can glue those together? Contrived simple example: diff $(echo 1 | stdout-to-temp-file) $(echo 2 | ...
2
votes
2answers
1k views

Difference between > and | with /dev/tty

When I run this command: echo "1" > /dev/tty # runs successfully but when I run this: echo "1" | /dev/tty #permission denied What is the difference between these two operators > and | and ...
6
votes
4answers
301 views

How to send stderr to stdout with a pipe to another command?

I'm trying to capture all of the output of a build operation, and send it to myprogram. I seem to only be able to capture part of it. This is what I'm trying: make clean && make ...
9
votes
4answers
957 views

Utility to buffer an unbounded amount of data in a pipeline?

Is there a utility that I can stick in a pipeline to decouple read and write speeds? $ producer | buf | consumer Basically, I want a utility buf that reads its input as fast as possible, storing it ...
4
votes
0answers
160 views

Repeatably generate a read error for testing? [duplicate]

I'm trying to test the error handling in some software, in particular what happens when an error occurs reading from a file or pipe. Is there a simple way to send a certain amount of data to stdout ...
4
votes
2answers
3k views

How to add a timestamp to each line of a logfile?

I have an external program which I can not edit. It writes its log to a file. How do I add a timestamp to each line while the program writes to the logfile? It does not write its output to stdout. ...
10
votes
2answers
2k views

Piping for loop output prevents local variable modification

I'm trying to write a simple bash function that takes, as its arguments, a number of files and/or directories. It should: Fully qualify the filenames. Sort them. Remove duplicates. Print all that ...
9
votes
2answers
880 views

How can I tell if the pipe buffer is full?

I am piping output from one program into some Perl I wrote. This is a long running process , sometimes days, so I want to find out where my bottlenecks are and try to open them up. I want to know if ...
14
votes
5answers
30k views

Difference between 2>&1 > output.log and 2>&1 | tee output.log

I wanted to know the difference between the following two commands 2>&1 > output.log and 2>&1 | tee output.log I saw one of my colleague use second option to redirect. I know ...
31
votes
2answers
21k views

How do I pass a list of files to grep

I am using find and getting a list of files I want to grep through. How do I pipe that list to grep?
1
vote
2answers
150 views

In tcsh how can I prepend 'cd ' to the output of a pipe?

As in, say I execute pwd to return the current directory and want to dump this in a script file so that I can come back, but I then need to prefix it with 'cd '?
2
votes
3answers
5k views

How to feed the results of date command into grep to filter results of another command

I need to use the result of a formatted date command (date +"%m/%d") as the grep filter to filter the results of another command that will display alerts on a system so that I only see alerts from the ...
16
votes
4answers
3k views

How to understand pipes

When I just used pipe in bash, I didn't think more about this. But when I read some C code example using system call pipe() together with fork(), I wonder how to understand pipes, including both ...
8
votes
2answers
865 views

Piping output from a segfaulting program

I have a script that calls a program (specifically, ttf2afm, part of tetex 3.0) that sometimes segfaults and sometimes doesn't. The information I need is always printed out before it segfaults, but ...
5
votes
2answers
1k views

Performance difference between stdin and command line argument

For some commands, it is possible to specify certain input as either stdin or a command line argument. Specifically, suppose command can take stdin input and a filename as command line argument, and ...
22
votes
4answers
4k views

Process substitution and pipe

I was wondering how to understand the following: Piping the stdout of a command into the stdin of another is a powerful technique. But, what if you need to pipe the stdout of multiple ...
1
vote
3answers
1k views

Ls with spaces + variables

I want to do something like this, but it doesn't save the variable after the piping ends: fs=( ) echo ${fs[@]} ls -A1 | while read f do echo ${fs[@]} fs+=( "$f" ) echo ${fs[@]} done echo ...
6
votes
6answers
4k views

Using data read from a pipe instead than from a file in command options

Per man definition, this command gets the input from a file. $ command -r FILENAME Suppose that FILENAME is a file containing a list of filenames, as it was generated using ls > FILENAME. How ...
0
votes
1answer
247 views

Is 'some_program <some_file' faster than 'cat some_file | some_program'? [duplicate]

Possible Duplicate: Should I care about unnecessary cats? Both would be functionally equivalent, but when using cat wouldn't it be slower because you have a process first reading the file ...
3
votes
2answers
1k views

Why is piped input okay to zenity, but <file malfunctions?

My question is as simple as what the zenity --text args say in the example... but what is causing this 100% CPU grab by the redirection? ...(and by the way, is this particular usage of < actually ...
2
votes
2answers
633 views

.DELETE_ON_ERROR behavior with make and pipelines

The .DELETE_ON_ERROR target will tell make to delete a target if a rule fails. But this doesn't work for pipelines, because the exit status value $? holds the value of the last program in the ...
2
votes
1answer
898 views

Pipe diff file into patch?

Is there a way to pipe the diff output into patch? The -i parameter is for specifying a diff file, but I just want to do it more dynamically, since I will be updating regularly against a directory ...
6
votes
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 ...
29
votes
3answers
2k views

Should I care about unnecessary cats?

A lot of command-line utilities can take their input either from a pipe or as a filename argument. For long shell scripts, I find starting the chain off with a cat makes it more readable, especially ...
6
votes
2answers
724 views

Is it possible to follow a command (run repeatedly)? as one would follow a file using tail -f?

I have a script which produces a file 'Detail.out'. I know that the script is completed whenever the file contains a certain number of lines (roughly 21025). So I find myself sitting at the command ...
11
votes
3answers
11k views

How to process/pipe TCPDUMPs output in realtime

If I want to tcpdump DNS requests by clients (on an OpenWrt 10.04 router), then I root@ROUTER:/etc# tcpdump -n -i br-lan dst port 53 2>&1 tcpdump: verbose output suppressed, use -v or ...
7
votes
3answers
1k views

Combine input from multiple files/pipes without clobbering lines or blocking?

Is there a tool that will take input from multiple files or pipes and write it to stdout, without blocking on reads, such that individual input lines come out intact? I basically want to multiplex a ...
3
votes
4answers
6k views

Passing pipeline value as parameter to xargs for use by eval echo

I have a text file that I'm using as a template, it looks like this: Hostname : $HOSTNAME Host Address : $HOSTADDRESS My bash script sets two variables, HOSTNAME and HOSTADDRESS, reads the ...
5
votes
1answer
1k views

How to pipe the result of 'date' command to 'mv' command

I want to rename my file to the current timestamp.I know how to get the current timestamp("date +%s") but how can I pipe it to 'mv' command?
87
votes
13answers
35k views

Get exit status of process that's piped to another

I have two processes foo and bar, connected with a pipe: $ foo | bar bar always exits 0; I'm interested in the exit code of foo. Is there any way to get at it?