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Top Forums UNIX for Beginners Questions & Answers WHy do we need both append and output directives? Post 303001570 by mojoman on Monday 7th of August 2017 01:54:16 PM
Old 08-07-2017
WHy do we need both append and output directives?

Hi,

I was reviewing a shell script and I found this line:

Code:
yum -y update >> >(/usr/bin/tee /var/log/file)

I have tried removing the >> directive and all that will occur is that the file will be created--nothing gets put in the file. If I put back the >> directive it works. If I remove the > the line fails. Why are both >> and > required?

Thanks.
 

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yum(8)																	    yum(8)

NAME
yum - Yellowdog Updater Modified SYNOPSIS
yum [options] [command] [package ...] DESCRIPTION
yum is an interactive, automated update program which can be used for maintaining systems using rpm command is one of: * install package1 [package2] [...] * update [package1] [package2] [...] * check-update * upgrade * remove [package1] [package2] [...] * list [...] * info [...] * provides [...] * clean [packages | headers | old-headers | all] Unless the --help or -h option is given, one of the above commands must be present. install is used to install the latest version of a package or group of packages while ensuring that all dependencies are satisfied. If no package matches the given package name(s), they are assumed to be a shell glob and any matches are then installed. update If run without any packages, update will update every currently installed package. If one or more packages are specified, Yum will only update the listed packages. While updating packages, yum will ensure that all dependencies are satisfied. If no package matches the given package name(s), they are assumed to be a shell glob and any matches are then installed. check-update Implemented so you could know if your machine had any updates that needed to be applied without running it interactively. Returns exit value of 100 if there are packages available for an update. Also returns a list of the pkgs to be updated in list format. Returns 0 and no packages are available for update. upgrade takes no arguments, this performs a complete upgrade of the system - good for distro-version changes as it includes packages obso- leting other packages in its updating calculations. remove is used to remove the specified packages from the system as well as removing any packages which depend on the package being removed. list can be used to list various information about available packages; more complete details are available in the List Options section below. provides can be used to find out which package provides some feature or file. Just use a specific name or a file-glob-syntax wildcards to list the packages available or installed that provide that feature or file. info can be used to list a description and summary information about available packages; takes the same arguments as in the List Options section below. clean is used to clean up various things which accumulate in the yup cache directory over time. More complete details can be found in the Clean Options section below. GENERAL OPTIONS
Most command line options can be set using the configuration file as well and the descriptions indicate the necessary configuration option to set. -h, --help Help; display a help message and then quit. -y Assume yes; assume that the answer to answer to any question which would be asked is yes. Configuration Item: assume-yes -r Replace conflicting files (equivalent to the RPM option of '--replacefiles --force'). Attention, this has a high 'shoot your own foot' possibility. Configuration Item: replacefiles -c [config file] Specifies the config file location. -d [number] Sets the debugging level to [number] - turns up or down the amount of things that are printed. -e [number] Sets the error level to [number] 0 - 10. 0 means print only critical errors about which you must be told. 1 means print all errors, even ones that are not overly important. 1+ means print more errors (if any) -e 0 is good for cron jobs. -t Tells yum to be tolerant of errors on the command line with regard to packages on the commandline. For example: if you request to install foo, bar and baz and baz is installed; yum won't error out complaining that baz is already installed. -R [time in minutes] Sets the maximum amount of time yum will wait before performing a command - it randomizes over the time. -C Tells yum to run entirely from cache - does not download or update any headers unless it has to to perform the requested action. LIST OPTIONS
The following are the ways which you can invoke yum in list mode. Note that all list commands include information on the version of the package. yum list [available] list all packages in the yum repositories available to be installed. yum list updates list all packages with updates available in the yum repositories. yum list [args] list the packages specified by args. If an argument does not match the name of a package, it is assumed to be a shell-style glob and any matches are printed. yum list installed list the packages specified by args. If an argument does not match the name of an available package, it is assumed to be a shell-style glob and any matches are printed. yum list extras list the packages installed on the system that are not available in any yum repository listed in the config file. CLEAN OPTIONS
The following are the ways which you can invoke yum in clean mode. yum clean packages Eliminate any cached packages from the system. Note that packages are not automatically deleted after they are downloaded. yum clean headers Eliminate all of the files which yum uses to determine the remote availablility of packages. Using this option will force yum to download all the headers the next time it is run. yum clean oldheaders Eliminate the old headers that yum no longer needs to determine the remote availablility of packages. yum clean [all] Runs yum clean packages and yum clean oldheaders as above. MISC
Proxy configuration If you would like to use a proxy with yum you can simply set a shell environment variable of http_proxy. Set it to the url for your proxy. Ex: "http://your_proxy:port/" FILES
/etc/yum.conf /var/cache/yum/ SEE ALSO
yum-arch (8), yum.conf (5) AUTHORS
Seth Vidal <skvidal@phy.duke.edu> BUGS
There of course aren't any bugs, but if you find any, they should be sent to the mailing list: yum@dulug.duke.edu Seth Vidal 2002 Jun 8 yum(8)
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