In my Linux environment, I am using a installed command that is of this format.
command1 -u <username> -p <password-file> ...
where in this password-file, it keeps a password value of the text format, such as "abc".
When running this command, I feel it is very inconvenient to every time create a file to hold this password value! So is there a way I can feed this "abc" value directly on this command line ???
Thanks,
Chun
If you are using bash (and if you are running in Linux, chances are good you are, or can) you can do:
command -u username -p <(echo abc)
which is equivalent to passing the name of a file with contents "abc\n".
This is surprisingly hard to search for.
The only thing I can find, are TRAP* functions, which can be triggered via various signals.
But I really want to watch all stdout/stderr, and have a function trigger if a certain string is matched.
(example: refreshing kerberos credentials. A command fails and emits a standard error message indicating I need to authenticate. I want to automatically run the command to do so ;)
The shell doesn't see a command's stdout/stderr if not piped to the shell. So, you need to redirect stdout/stderr to your zsh function. But you can also send them to both your zsh function and somewhere else. For instance:
your_command 2>&1 | tee >(your_zsh_function)
or
your_command |& tee >(your_zsh_function)
or
your_command >>(your_zsh_function) >>/dev/tty 2>&1
your_zsh_function will grep its input for a string match. A drawback is that you may have buffering problems.
But concerning your example, if I understand correctly, you may want to use the expect utility: "programmed dialogue with interactive programs".
I have a problem with the nohup command.
When I run my job, I have a lot of data. The output nohup.out becomes too large and my process slows down. How can I run this command without getting nohup.out?
The nohup command only writes to nohup.out if the output would otherwise go to the terminal. If you have redirected the output of the command somewhere else - including /dev/null - that's where it goes instead.
nohup command >/dev/null 2>&1 # doesn't create nohup.out
Note that the >/dev/null 2>&1 sequence can be abbreviated to just >&/dev/null in most (but not all) shells.
If you're using nohup, that probably means you want to run the command in the background by putting another & on the end of the whole thing:
nohup command >/dev/null 2>&1 & # runs in background, still doesn't create nohup.out
On Linux, running a job with nohup automatically closes its input as well. On other systems, notably BSD and macOS, that is not the case, so when running in the background, you might want to close input manually. While closing input has no effect on the creation or not of nohup.out, it avoids another problem: if a background process tries to read anything from standard input, it will pause, waiting for you to bring it back to the foreground and type something. So the extra-safe version looks like this:
nohup command </dev/null >/dev/null 2>&1 & # completely detached from terminal
Note, however, that this does not prevent the command from accessing the terminal directly, nor does it remove it from your shell's process group. If you want to do the latter, and you are running bash, ksh, or zsh, you can do so by running disown with no argument as the next command. That will mean the background process is no longer associated with a shell "job" and will not have any signals forwarded to it from the shell. (A disowned process gets no signals forwarded to it automatically by its parent shell - but without nohup, it will still receive a HUP signal sent via other means, such as a manual kill command. A nohup'ed process ignores any and all HUP signals, no matter how they are sent.)
Explanation:
In Unixy systems, every source of input or target of output has a number associated with it called a "file descriptor", or "fd" for short. Every running program ("process") has its own set of these, and when a new process starts up it has three of them already open: "standard input", which is fd 0, is open for the process to read from, while "standard output" (fd 1) and "standard error" (fd 2) are open for it to write to. If you just run a command in a terminal window, then by default, anything you type goes to its standard input, while both its standard output and standard error get sent to that window.
But you can ask the shell to change where any or all of those file descriptors point before launching the command; that's what the redirection (<, <<, >, >>) and pipe (|) operators do.
The pipe is the simplest of these... command1 | command2 arranges for the standard output of command1 to feed directly into the standard input of command2. This is a very handy arrangement that has led to a particular design pattern in UNIX tools (and explains the existence of standard error, which allows a program to send messages to the user even though its output is going into the next program in the pipeline). But you can only pipe standard output to standard input; you can't send any other file descriptors to a pipe without some juggling.
The redirection operators are friendlier in that they let you specify which file descriptor to redirect. So 0<infile reads standard input from the file named infile, while 2>>logfile appends standard error to the end of the file named logfile. If you don't specify a number, then input redirection defaults to fd 0 (< is the same as 0<), while output redirection defaults to fd 1 (> is the same as 1>).
Also, you can combine file descriptors together: 2>&1 means "send standard error wherever standard output is going". That means that you get a single stream of output that includes both standard out and standard error intermixed with no way to separate them anymore, but it also means that you can include standard error in a pipe.
So the sequence >/dev/null 2>&1 means "send standard output to /dev/null" (which is a special device that just throws away whatever you write to it) "and then send standard error to wherever standard output is going" (which we just made sure was /dev/null). Basically, "throw away whatever this command writes to either file descriptor".
When nohup detects that neither its standard error nor output is attached to a terminal, it doesn't bother to create nohup.out, but assumes that the output is already redirected where the user wants it to go.
The /dev/null device works for input, too; if you run a command with </dev/null, then any attempt by that command to read from standard input will instantly encounter end-of-file. Note that the merge syntax won't have the same effect here; it only works to point a file descriptor to another one that's open in the same direction (input or output). The shell will let you do >/dev/null <&1, but that winds up creating a process with an input file descriptor open on an output stream, so instead of just hitting end-of-file, any read attempt will trigger a fatal "invalid file descriptor" error.
nohup some_command > /dev/null 2>&1&
That's all you need to do!
Have you tried redirecting all three I/O streams:
nohup ./yourprogram > foo.out 2> foo.err < /dev/null &
You might want to use the detach program. You use it like nohup but it doesn't produce an output log unless you tell it to. Here is the man page:
NAME
detach - run a command after detaching from the terminal
SYNOPSIS
detach [options] [--] command [args]
Forks a new process, detaches is from the terminal, and executes com‐
mand with the specified arguments.
OPTIONS
detach recognizes a couple of options, which are discussed below. The
special option -- is used to signal that the rest of the arguments are
the command and args to be passed to it.
-e file
Connect file to the standard error of the command.
-f Run in the foreground (do not fork).
-i file
Connect file to the standard input of the command.
-o file
Connect file to the standard output of the command.
-p file
Write the pid of the detached process to file.
EXAMPLE
detach xterm
Start an xterm that will not be closed when the current shell exits.
AUTHOR
detach was written by Robbert Haarman. See http://inglorion.net/ for
contact information.
Note I have no affiliation with the author of the program. I'm only a satisfied user of the program.
Following command will let you run something in the background without getting nohup.out:
nohup command |tee &
In this way, you will be able to get console output while running script on the remote server:
sudo bash -c "nohup /opt/viptel/viptel_bin/log.sh $* &> /dev/null" &
Redirecting the output of sudo causes sudo to reask for the password, thus an awkward mechanism is needed to do this variant.
If you have a BASH shell on your mac/linux in-front of you, you try out the below steps to understand the redirection practically :
Create a 2 line script called zz.sh
#!/bin/bash
echo "Hello. This is a proper command"
junk_errorcommand
The echo command's output goes into STDOUT filestream (file descriptor 1).
The error command's output goes into STDERR filestream (file descriptor 2)
Currently, simply executing the script sends both STDOUT and STDERR to the screen.
./zz.sh
Now start with the standard redirection :
zz.sh > zfile.txt
In the above, "echo" (STDOUT) goes into the zfile.txt. Whereas "error" (STDERR) is displayed on the screen.
The above is the same as :
zz.sh 1> zfile.txt
Now you can try the opposite, and redirect "error" STDERR into the file. The STDOUT from "echo" command goes to the screen.
zz.sh 2> zfile.txt
Combining the above two, you get:
zz.sh 1> zfile.txt 2>&1
Explanation:
FIRST, send STDOUT 1 to zfile.txt
THEN, send STDERR 2 to STDOUT 1 itself (by using &1 pointer).
Therefore, both 1 and 2 goes into the same file (zfile.txt)
Eventually, you can pack the whole thing inside nohup command & to run it in the background:
nohup zz.sh 1> zfile.txt 2>&1&
You can run the below command.
nohup <your command> & > <outputfile> 2>&1 &
e.g.
I have a nohup command inside script
./Runjob.sh > sparkConcuurent.out 2>&1
I'm quite new to cron and crontab.
I've edited the crontab file and I need to execute manually one of commands so I can try it and test it beforehand. How do I do that? If it fails, is there a mode that shows the errors?
Write a shell script that you can test.
Execute that shell script from the crontab.
Remember that cron provides barely any environment - so your script may have to fix that. In particular, your profile will not be used.
Do not get fancy with what you put in the crontab.
Build a debug mode into your shell script.
No, there isn't specifically a mode that shows errors. Usually, if the cron job witters, the output is emailed to you. That is, it sends standard output and standard error information to you if the executed command writes anything to either standard output or standard error.
On MacOS X (10.6.7), the environment I got was (via a crontab entry like 12 37 17 5 * env >/tmp/cron.env):
SHELL=/bin/sh
USER=jleffler
PATH=/usr/bin:/bin
PWD=/Users/jleffler
SHLVL=1
HOME=/Users/jleffler
LOGNAME=jleffler
_=/usr/bin/env
Of those, PWD, _ and SHLVL are handled by the shell. So, to test your script reliably in a cron-like environment, use:
(cd $HOME
env -i \
SHELL=/bin/sh \
USER=$USER \
PATH=/usr/bin:/bin \
HOME=$HOME \
LOGNAME=$LOGNAME \
/path/to/script/you/execute ...
)
The -i option to env means 'ignore all inherited enviroment'; the script will see exactly the five values specified plus anything the shell specifies automatically. With no arguments, env reports on the environment; with arguments, it adjusts the environment and executes a command.
To execute a script "manually" you first have to make it executable by doing:
$ chmod +x yourScriptName
Then do either
$ ./yourScriptName
if you execute it from its path or
$ /full/path/to/yourScriptName
from anywhere.
I have two unix machines, both running AIX 5.3
My $HOME is mounted on machine1.
Using NFS, login machine2 will go to the same $HOME
I login machine2 first, then machine1.
Both using telnet.
The 2 sessions will share the same .sh_history file.
I found out that the fc -l behavior very strange.
In machine2, I issue the commands in telnet:
fc -l
ksh fc -l
Both give the same output.
In machine1,
fc -l
ksh fc -l
give DIFFERENT results
The result for ksh fc -l
is the same as /usr/bin/fc -l
Also, when I run a script like this:
#!/usr/bin/ksh
fc -l
The result is same as /usr/bin/fc -l
Could anyone tell me what happened?
Alvin SIU
Ah, wisdom of the ancients... (Since this post is over a year old.)
Anyway, I just encountered this problem in Solaris 10. Issue seems to be this: When you define a function in /etc/profile, or in any file called by /etc/profile, your HISTFILE variable gets ignored by the Korn shell, and the shell instead uses ".sh_history" when accessing its history. Not sure why this is.
Result is that you see other root shell's commands. You can test it with :
lsof -p $$
or
cat /proc/$$/fd/63
It's possible that the login shell is not ksh or that $HISTFILE is being reset. One thing you can do is echo $HISTFILE in the various situations and see if it's different. Another thing to check is to see what shell you're in using ps.
Bash (default $HOME/.bash_history), for example, will have a different $HISTFILE than ksh (default $HOME/.sh_history).
Another possible reason for the difference is that the builtin fc may be able to see in-memory history that hasn't been written to disk yet (which the external /usr/bin/fc wouldn't be able to see). If this is true, it may be version dependent. Bash, for example, doesn't write history to the file until the shell exits. Ksh (at least the version I'm using) writes it immediately.