Carefully analyze the difference between what you have done before and what you are doing now and you will understand whats wrong yourself:
versus
"cat test1" is a process, yes? It has some output, which you can observe by issuing this command, it will print the content of the file, line by line.
Now you pipe the output of this process into another process, which is set up by "while ... do .... done". To the outside this counts as one process, even if it contains several other processes inside.
In the second case you pipe the output into a completely different process, a command called "read", which tries to fill a variable with content. In the first case "read" is only invoked by the while-loop as a sub-process and is presented one line after the other which it dutifully assigns to the variable $line. In the second case it is fed the whole output of the first process at once. What is poor "read" supposed to do, hm?
Hello Awk Gurus,
Can anyone of you help me with the below problem. I have got a file having data in below format
pmFaultyTransportBlocks
-----------------------
9842993
pmFrmNoOfDiscRachFrames
-----------------------
NULL
pmNoRecRandomAccSuccess
-----------------------... (4 Replies)
Hi!
I am writing a script handling downloading list of files and I have to check whether file is present locally and if not finished than continue downloading. To do so I have to compare sizes of remote file and local file.
To check remote file size I have to parse something like this:
... (2 Replies)
Hi all
I use aix (sadly).
I've got a file consisting of fields separated by commas, I need a sed or awk command that will delete all spaces between two commas as long as there are only spaces between the commas.
eg
,abc, ,sd , ,dr at
would become
,abc,,sd ,,dr at
I have... (53 Replies)
Hello,
i have a file, i open the file and read the line, i want to get the first item in the csv file and also teh third+6 item and wirte it to a new csv file. only problem is that using echo it takes TOO LONG:
please help a newbie. below is my code:
WorkingDir=$1
FileName=`cut -d ',' -f... (2 Replies)
Hi all,
I have a list that I would like to parse with awk/sed. The list is contains entries such as:
JournalTitle: Biochemistry
JournalTitle: Biochemistry and cell biology = Biochimie et biologie cellulaire
JournalTitle: Biochemistry and experimental biology
JournalTitle: Biochemistry and... (6 Replies)
HI All,
I am new to unix. I have a file would like to do some editing by using awk, cut and sed. Could anyone help?
This file contain 100 lines. There are one line for example:
2,"102343454",5060,"579668","579668","579668","SIP",,,"825922","035885221283026",1,268,"00:59:00.782 APR 17... (2 Replies)
here is what i want to achieve... consider a file contains below contents. the file size is large about 60mb
cat dump.sql
INSERT INTO `table1` (`id`, `action`, `date`, `descrip`, `lastModified`) VALUES (1,'Change','2011-05-05 00:00:00','Account Updated','2012-02-10... (10 Replies)
Dear All,
Can anyone help to remove the , bewteen "" in a string by using sed or awk?
e.g.
input : 1,4,5,"abcdef","we,are,here",4,"help hep"
output:1,4,5,"abcdef","wearehere",4,"help hep"
Thanks,
Mimi (5 Replies)
Sorry for the long/weird title but I'm stuck on a problem I have. I have this XML file:
</member>
<member>
<name>TransactionID</name>
<value><string>123456789123456</string></value>
</member>
<member>
<name>Number</name>
... (9 Replies)
I have a file comp.pkglist which mention package version and release . In 'version change' and 'release change' line there are two versions 'old' and 'new' Version Change: --> Release Change: -->
cat comp.pkglist
Package list: nss-util-devel-3.28.4-1.el6_9.x86_64
Version Change: 3.28.4 -->... (1 Reply)
Discussion started by: Paras Pandey
1 Replies
LEARN ABOUT MOJAVE
ipc::open2
IPC::Open2(3pm) Perl Programmers Reference Guide IPC::Open2(3pm)NAME
IPC::Open2 - open a process for both reading and writing using open2()
SYNOPSIS
use IPC::Open2;
$pid = open2(*CHLD_OUT, *CHLD_IN, 'some cmd and args');
# or without using the shell
$pid = open2(*CHLD_OUT, *CHLD_IN, 'some', 'cmd', 'and', 'args');
# or with handle autovivification
my($chld_out, $chld_in);
$pid = open2($chld_out, $chld_in, 'some cmd and args');
# or without using the shell
$pid = open2($chld_out, $chld_in, 'some', 'cmd', 'and', 'args');
waitpid( $pid, 0 );
my $child_exit_status = $? >> 8;
DESCRIPTION
The open2() function runs the given $cmd and connects $chld_out for reading and $chld_in for writing. It's what you think should work when
you try
$pid = open(HANDLE, "|cmd args|");
The write filehandle will have autoflush turned on.
If $chld_out is a string (that is, a bareword filehandle rather than a glob or a reference) and it begins with ">&", then the child will
send output directly to that file handle. If $chld_in is a string that begins with "<&", then $chld_in will be closed in the parent, and
the child will read from it directly. In both cases, there will be a dup(2) instead of a pipe(2) made.
If either reader or writer is the null string, this will be replaced by an autogenerated filehandle. If so, you must pass a valid lvalue
in the parameter slot so it can be overwritten in the caller, or an exception will be raised.
open2() returns the process ID of the child process. It doesn't return on failure: it just raises an exception matching "/^open2:/".
However, "exec" failures in the child are not detected. You'll have to trap SIGPIPE yourself.
open2() does not wait for and reap the child process after it exits. Except for short programs where it's acceptable to let the operating
system take care of this, you need to do this yourself. This is normally as simple as calling "waitpid $pid, 0" when you're done with the
process. Failing to do this can result in an accumulation of defunct or "zombie" processes. See "waitpid" in perlfunc for more
information.
This whole affair is quite dangerous, as you may block forever. It assumes it's going to talk to something like bc, both writing to it and
reading from it. This is presumably safe because you "know" that commands like bc will read a line at a time and output a line at a time.
Programs like sort that read their entire input stream first, however, are quite apt to cause deadlock.
The big problem with this approach is that if you don't have control over source code being run in the child process, you can't control
what it does with pipe buffering. Thus you can't just open a pipe to "cat -v" and continually read and write a line from it.
The IO::Pty and Expect modules from CPAN can help with this, as they provide a real tty (well, a pseudo-tty, actually), which gets you back
to line buffering in the invoked command again.
WARNING
The order of arguments differs from that of open3().
SEE ALSO
See IPC::Open3 for an alternative that handles STDERR as well. This function is really just a wrapper around open3().
perl v5.18.2 2013-11-04 IPC::Open2(3pm)