Programming :: BASH: Get PID Of First Command In Pipe
Aug 11, 2010
I understand that $! is the PID of a command. For example:
Code: #!/bin/bash
myprogram &
echo "PID of myprogram is $!"
I'd like to send the output of "myprogram" to both console and to a log file using the "tee" command but I also want to store the PID of "myprogam". Something like this:
Code: #!/bin/bash
myprogram | tee ./logfile &
echo "PID of myprogram is $!"
The problem is that $! is now the PID of "tee" rather than the PID of "myprogram".
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Apr 22, 2010
My question deals with me creating a name pipe (file) in the my /group directory called chat.I then have to write a script to read from the named pipe and save data into a file called chat.log until the words End of File are passed to the program.
-When I created the named pipe file (chat) I used the mknod chat p command..Is this the correct command to create a named pipe file? -Then I'm having trouble with my script and how to make it run until the words End of File are entered in. This is what I have so far.
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Mar 2, 2011
I've written a simple server in linux used fork to create a FIFO pipe.The server create two FIFO pipe.One for server read data from client and write data to client.Then another pipe for client read data from server and write data to server.When the server read data from a client used server-pipe and then write data to client.But ,if the client no read open the pipe,the server side write will be crashed because of a broken-pipe SIGPIPE. How to check whether the read side is opened?Or,how to catch the SIGPIPE,and then my server will still execute on,not crashed!!
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May 13, 2011
Have this script which is reading in a series of files, one at a time with while-do-done loop, each file goes through various greps/awk's where this info is then saved to various files for later use. i.e....
Script is being run on Linux Red Hat,
In one of the grep/awk's the output (currently) are 2 columns (min max), i.e....| awk '{print $1, $2}' | sort -u which outputs (e.g.)
The number of "min max" pairs varies from file to file. Want to output a single column of unique numbers from the min max pairs & get the number of them for input to a file...i.e...
Where <PROCESS> is some process/technique that will generate a single column of integers (increment of 1) to pipe into the next one (sort -u)
i.e. (example from above)
Have tried command seq - only works for single pair input i.e.
Is there any command like seq etc which will output a single column based on a input of min max numbers (increment 1) to pipe onwards to next command?
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Aug 21, 2010
I don't quite understand how pipes work in bash. I know that it takes an output from one command as the input in another command. What an output is I can get because it's what the command prints out to the screen. But how do I know what input a command will take? Here is an example I thought would work:
Which gem | rm
Unfortunately it didn't.
Which gem prints out "/usr/bin/gem" so that must be the output right? I thought that was given to rm so it would be "rm /usr/bin/gem" but I was wrong. How do I know what input a command takes?
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Jul 25, 2010
Two processes are communicating through a pipe: A | B. A is writing data faster than B is reading it in. Is there any way to have A limit its writing rate to match B's reading rate?
AFAIK the pipe will get full, and will make A's writing block, waiting for B to read in more data. But is there a way to limit A's writing rate before the pipe fills up? (In a way it's like having a pipe with a really small capacity, but as far as I know pipe capacity is a constant compiled into the kernel.)
Code:
EXAMPLE FOR CLARIFICATION
Right now the command is printing out the following in 1-second intervals:
But with flow control it should print out (again in 1-second intervals):
...since "date" would block on the writing loop due to the slow reading loop.
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Jul 14, 2011
Distro: Centos 5, PHP 5I have done a bit research on running bash commands from php and there was little success. This is my relevant php script
<?php
echo exec('pwd');
?>
[code]...
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Mar 9, 2011
I am trying to grep multiple numbers from file, grep does have the -f option for that.
Code: grep -f <`seq 500 520` /etc/passwd I know this could be done with
Code: for i in `seq 500 520`; do grep "$i" /etc/passwd; done But my question is fare more behind this example. It is possible to redirect one command output which will be treat as a content of file for another command ?
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Mar 24, 2011
I often want to extract some info using awk from a variable/filename while running other things using xargs and sh. Below is an example:
Code: ls -1 *.txt | xargs -i sh -c 'NEW=`echo $0 | awk -F'_' '{print $1}'`; echo $NEW' {}
In the above case I would like to grab just the first field from a filename (delimited by '_') from within an sh command. This is a simplified example, where normally I would be doing some further data processing with the sh command(s).
The error message that I get is:
Code: }`; echo $NEW: -c: line 0: unexpected EOF while looking for matching ``'
}`; echo $NEW: -c: line 1: syntax error: unexpected end of file.
I haven't been able to figure out how to escape the awk command properly.
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Feb 22, 2010
Example from zenity:
Code:
#!/bin/sh
(
[code].....
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Apr 20, 2011
I have script which does file locking via flock and then writing it's pid into that file. It perfectly works being run by hand in terminal, running under cron on Debian, but somehow fails being run under cron on Centos 5.6. Script part and straced outputs are below.
bash code:
#setting lock
mylog "setting lockfile $LOCKFILE"
exec 200<> $LOCKFILE
[code]....
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Sep 29, 2010
I have the following command that works Code: ssh root{at}IPADDRESS 'vim-cmd vmsvc/power.getstate 64 | grep Powered | awk "{ print $2}"' Which outputs the following text:- Powered on I would like to Append some text so the output is:- Ubuntu Server: Powered on Every different variation that I have tried ends up in an unexpected token.
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Mar 24, 2011
I am trying to process a column separated data file, with a few bash command. For example, I have
Code:
file1 aaaa yes
file2 aaaa no
file3 bbbb yes
Let say I want to create new file with the output of first column and do something else with the output of 3rd column. Of course there are many ways to process this data file, but I wish to know by using awk, how could I do it. I'm trying:
Code:
awk '{system("touch $1")}' datafile
but the shell command will not able to get the awk '$1' output. How do I get this done ? And for another question, if the data file contains the variable name of a shell variable, how could I make use of it during a awk output ? For example I have a datafile1:
Code:
server1 yes
server2 no
And in another server declaration data file, I got this datafile2:
Code:
server1=xxx1
server2=yyy1
And in my awk script, I want to achieve something like (the syntax is definitely wrong, just to demonstrate what I assume it will like):
[code]....
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Apr 19, 2010
I move a page from a server in SuSe to Debian and this script was working well but when I move the page to a Debian base server it is sending in the logs the following message:
cat: write error: Broken pipe, referer: [URL]
The cgi does the following, read a db file plain text that repeat each 15 lines an information where to look the seraching info. if it is there sends to the output the 15 lines block. but it was not sending errors in suse distro, does anybody knows why the cat's line are sending "cat: write error: Broken pipe," if I am not writing or making a pipe with ">" to none file.
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Jan 20, 2011
As part of my script I need to compress a 50Gb file. but I need to check that the compressed is not corrupt if it is ok it will then send it over if not it will report an error.
cd /home/ops/Desktop/temp
tar czvf backup-"$(date +%d-%b-%y)".tgz /home/ops/Desktop/temp
I need some here to check the compress file then somelike if the file is
if
send the file
else
send an e-mail reporting a failure
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Mar 1, 2011
I am having all sorts of trouble trying to assign a variable within an awk script with the system command. I know there is a lot of ways around this problem, but for efficiency reasons, I would like to, within my awk script, do something like
system(x=3)
or
system(x=NR)
and, latter on the shell script which calls the awk script, use the variable $x. But nothing is passed to x. I have already tried things like
command = "x=3"
system(command)
and also used a pipeline within the system to pipe it to /bin/sh In fact tried a lot of stuff like that, using $(( )) etc etc etc I can create directories e write to files (yes, i could write to a file and read from there, but I dont think it is efficient, plus I am puzzled).
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May 15, 2011
I want to write a bash script that will launch a command when ever I plug my phone in. how would I monitor the port in a script.
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Apr 6, 2011
I'm trying to do something here:: I'm writing a bash script, I want to [open a new terminal and run a bash command in it] inside the script. I tried to use this, but apparently I get syntax errors.
Quote:
#! /bin/bash
echo "echo Something" > ~/Second.sh
chmod +x ~/Second.sh
xterm -e sh -c ./Second.sh
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Jul 8, 2011
Bash 3.1.7
Suppose this bash script:
Code:
#!/bin/bash
ls foo
I would like the output to be
Code:
ls foo
foo
That is, the command is first echoed then executed. Is it possible to do this? Or is the only way to debug the script?
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Sep 12, 2010
Is it possible to organize bash script output of which is like on top command i.e. monitoring every let's say 1 sec and old information would cleared?
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Jul 11, 2010
This pretend to be a script for rename a lot of files automatically. So I put the list of files in an array named @lista. But, as you can see, at the end of the command I use a sed filter to print out a backslash for those files that have spaces in their names, so the path for those files could be rightly interpreted.
But there's no way I could print a backslash. It works well when I use the Perl's sed substitution s///, but I need every path in the array to be fixed.
I'd like to add that the bash command works perfectly well alone. I mean outside the Perl script.
This is de command line with the sed filter:
Code:
And this is what it brings:
Code:
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May 27, 2009
I am new to scripting and been working on this bash script for awhile now. I been researching this problem, but I can't seem to find a solution. I was wondering if someone could please help me out. Here is my script:
#!/bin/bash
NO="ps -ef | grep NO | grep -v grep"
NOWC=`ps -ef | grep NO | grep -v grep | wc -l`
[code].....
I cannot get this script to run the "ps -ef" command on the client. It get its value from the host machine that I am running this script from. I need this command to execute on the client. When I run the command (ps -ef | grep NO | grep -v grep) on the client, I get something back. Here is what I get when I try to debug the script.
XX# ./test_ps5.sh XXXXX
+ NO='ps -ef | grep NO | grep -v grep'
++ ps -ef
[code]....
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Oct 19, 2010
I want to delete all files within a specific folder without actually deleting the folder, what is a good bash command for this?. I found this one but encountered some errors even though I am executing it within the specific folder:
useratdebian:/home/user/folder# find . -type f -exec rm -rf {} ;
[1] 5052
useratdebian:/home/user/folder# find: missing argument to `-exec'
[1]+ Exit 1 find . -type f -exec rm -rf
The command as it appears is:
find . -type f -exec rm -rf {} ;
how to delete only the files contained within the folder called "folder" for example?
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Jul 16, 2010
I'm writing a Bash script to take IPTC keywords from a text file and write them, via Exiv2, to several (first batch is 100) JPEG files in a single directory. The script has one while loop inside another while loop, both terminated, but I'm pretty sure that's not my problem. I think it's how I'm incrementing the "counter" variable, although it could also be the method of parsing the text lines from the file (using cut with delimiters that have worked fine in simpler scripts).
Here's the code as I've worked it up to this point.
Code:
And yes, "keywords" checks out in Crimson Editor, Emacs GUI and nano as an ASCII file with UNIX line endings. No issues on that score.
Feeding each line consecutively into a terminal (excepting the exiv2 command) works fine: each variable echoes with the part of the text line used as a variable value as it should, even when the b variable is incremented the quick&dirty way (up arrow three commands and hit enter).
Running the above script in eval mode (sh -x) stalls after setting the b variable to one and reading in the first line of text. I'd like to know why. I'd also like some advice on another reliable method of parsing the read-in lines.
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Feb 12, 2011
I'm trying to execute the following command within a bash script:
Code:
tac /var/log/system.log | head -1
The script I wrote is:
[code]...
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Feb 16, 2011
Writing script to create backup of file by adding datetime to file name. Basically test for file presence if there, cp with datetime then rm original cp works fine from command line but get cannot stat `full path to file': No such file or directory
Code:
Here are the errors: cp: cannot stat `~/html/CVP_dadamail/.dada_files/.logs/errors.txt': No such file or directory rm: cannot remove `...': No such file or directory
The for statement is a placeholder as I have same file to backup out of several directories. using "bash -x scriptname" -OR- inserting echos, I can see I've constructed the strings properly. Believing it might be related to the hidden directories, I tried setting the shopt "glob" options to no avail.
Ultimately I'll add the other directories to the for loop and then run this from a cron job, so if you see potential pitfalls knowing I'm headed in that direction...believe construct would be
Code:
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Jan 26, 2011
I have a command that outputs n lines of text, and I want to place each line into an array element, but I can't seem to get the syntax correct
So my command is this:
cat $configfile | sed -n '/cluster:'$clustername'/,/cluster/ p' | awk /host/
Which produces many lines depending on the value of $clustername. I'd like to get each line as elements of an array.
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Mar 22, 2010
I'm trying to write a bash script program in the Linux command terminal that will write to a fellow user and then continue reading down the program. this is what i have (kind of explains the idea too):
#!/bin/sh
clear
echo "this is before the write command"
write jcummins
this message should go to jerry
echo "the message didn't send and this string will not appear"
echo "it appears it has stopped at the write command"
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May 9, 2010
I'm looking for an mp3 file in the firefox cache folder.I was thinking I could run the command 'find -size +2M' and pipe that output into the 'file' command to tell me which is an mp3, something like thisfind -size +2M | fileBut this doesn't work, what am I doing wrong?This is output Usage: file [-bcikLhnNrsvz0] [-e test] [-f namefile] [-F separator] [-m magicfiles] file...file -C -m magicfilesTry `file --help' for more information.
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Feb 14, 2011
I wanted to find and replace a string from a perl file. I have written a script in bash which runs the following command.
perl -pi -e "s/$findstring/$replacestring/" testfile
where as $findstring = print F_WC_TMP"$line
";
and $replaceString = $line = join ' ', split ' ', $line; print F_WC_TMP"$line
";
But when I am running the above command, i think it is replacing the $findstring with the above mentioned string and hence it contains a $line, it is looking for the variable $line and not finding the exact string. I am confused about how to search for a string that contains $ in it and replace it with another $string.
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