piping in UNIX doubt

Posted by Happy Mittal on Stack Overflow See other posts from Stack Overflow or by Happy Mittal
Published on 2010-04-15T09:33:01Z Indexed on 2010/04/15 9:43 UTC
Read the original article Hit count: 298

Filed under:

piping

|

unix

In The Unix Programming Environment by K & P, it is written that
" The programs in a pipeline actually run at the same time, not one after another.
This means that programs in a pipeline can be interactive;"

How can programs run at same time?
For ex: $ who | grep mary | wc -l
How grep mary will be executed until who is run or how wc -l will be executed until it knows results of previous programs?

© Stack Overflow or respective owner

Related posts about piping

Pipe implementation

as seen on Stack Overflow - Search for 'Stack Overflow'
I am trying to implement a linux shell that supports piping. I have already done simple commands, commands running in background, redirections, but piping is still missing. I have already read about it and seen some snippets of code, but still haven't been able to sort out a working solution. What… >>> More
Piping a bash variable into awk and storing the output

as seen on Stack Overflow - Search for 'Stack Overflow'
Hello, To illustrate my problem, TEST="Hi my name is John" OUTP=`echo $TEST | awk '{print $3}'` echo $OUTP What I would expect this to do is pass the $TEST variable into awk and store the 3rd word into $OUTP. Instead I get "Hi: not found", as if it is expecting the input to be a file. If I… >>> More
Trouble with piping through sed

as seen on Stack Overflow - Search for 'Stack Overflow'
I am having trouble piping through sed. Once I have piped output to sed, I cannot pipe the output of sed elsewhere. wget -r -nv http://127.0.0.1:3000/test.html Outputs: 2010-03-12 04:41:48 URL:http://127.0.0.1:3000/test.html [99/99] -> "127.0.0.1:3000/test.html" [1] 2010-03-12 04:41:48 URL:http://127… >>> More
Unix Piping using Fork and Dup

as seen on Stack Overflow - Search for 'Stack Overflow'
Lets say within my program I want to execute two child processes, one to to execute a "ls -al" command and then pipe that into "wc" command and display the output on the terminal. How can I do this using pipe file descriptors so far the code I have written: An example would be greatly helpful int… >>> More
linux piping ( convert -> pdf2ps -> lp)

as seen on Stack Overflow - Search for 'Stack Overflow'
Ok, so I can print a pdf doing: pdf2ps file.pdf - | lp -s But now I want to use convert to merge several pdf files, I can do this with: convert file1.pdf file2.pdf merged.pdf which merges file1.pdf and file2.pdf into merged.pdf, target can be replaced with '-'. Question How could I pipe convert… >>> More

Related posts about unix

polkit: disable all users except those in group wheel?

as seen on Ask Ubuntu - Search for 'Ask Ubuntu'
Is it possible to do the following using 1 polkit .pkla file? Disable all users except those in the wheel group from using polkit. The users in the wheel group will need to provide the root password when using polkit. /etc/polkit-1/localauthority/50-local.d/wheel-only.pkla [disable all users… >>> More
How to find other end of unix socket connection?

as seen on Server Fault - Search for 'Server Fault'
I have a process (dbus-daemon) which has many open connection over UNIX sockets. One of these connections is fd #36: =$ ps uw -p 23284 USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND depesz 23284 0.0 0.0 24680 1772 ? Ss 15:25 0:00 /bin/dbus-daemon --fork… >>> More
Meaning of directories on Unix and Unix like systems

as seen on Server Fault - Search for 'Server Fault'
I've been using Linux for a couple of years now but I still haven't figured out what the origin or meaning of some the directory names are on Unix and Unix like systems. E.g. what does etc stand for or var? Where does the opt name come from? And while we're on the topic anyway. Can someone give a… >>> More
Easy understanding of UNIX and UNIX shell scripting!!

as seen on Stack Overflow - Search for 'Stack Overflow'
Hi All, I am beginner to UNIX,UNIX Shell Scripting. Can you please guide me through any excellent sites for unix(which are easy to understand),some study materials(tutorials),video tutorials. Please help!! Thanks! >>> More
Is Mac OS X a licensed Unix or Unix-like clone that conforms to Unix specification?

as seen on Super User - Search for 'Super User'
Is Mac OS X developed on a licensed Unix or is it a Unix-like clone that, unlike Linux, conforms to Unix specification well enough to be registered as a Unix OS. Not until Leopard, Mac OS X did not gain the Unix certification. But in Leopard, Terminal still print: GNU bash, version 3.2.48(1)-release… >>> More