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Top Forums Shell Programming and Scripting meaning of today=${1:-${today}} Post 302612715 by Vidhyaprakash on Monday 26th of March 2012 09:35:14 AM
Old 03-26-2012
meaning of today=${1:-${today}}

what does today=${1:-${today}} mean???

I saw a script which has these two lines:
today=`date '+%y%m%d'`
today=${1:-${today}}

but both gives the same value for $today

Code:
user:/export/home/user>today=`date '+%y%m%d'`
user:/export/home/user>echo $today
120326
user:/export/home/user>today=${1:-${today}}
user:/export/home/user>echo $today
120326
user:/export/home/user>today=
user:/export/home/user>today=${1:-${today}}
user:/export/home/user>echo $today
 
user:/export/home/user>

Can someone please let me know, what actually today=${1:-${today}}
means???
 

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NNGOBACK(1)						      General Commands Manual						       NNGOBACK(1)

NAME
nngoback - make news articles unread on a day-by-day basis (nn) SYNOPSIS
nngoback [ -NQvi ] [-d] days [ group ]... DESCRIPTION
nngoback will rewind the .newsrc record file of nn(1) one or more days. It can be used to rewind all groups, or only a specified set of groups. In other words, nngoback can mark news articles which have arrived on the system during the last days days unread. Only subscribed groups that occur in the current presentation sequence are rewound. That means that if no group arguments are specified, all groups occurring in the sequence defined in the init file will be rewound. Otherwise, only the groups specified on the argument line will be rewound. When a group is rewound, the information about selections, partially read digests etc. are discarded. It will print notifications about this unless the -Q (quiet) option is used. If the -i (interactive) option is specified, nngoback will report for each how many articles can be marked unread, and ask for confirmation before going back in that group. If the -v (verbose) option is specified, nngoback will report how many articles are marked unread. If the -N (no-update) option is specified, nngoback will perform the entire goback operation, but not update the .newsrc file. If you are not up-to-date with your news reading, you can also use nngoback to catch up to only have the last few days of news waiting to be read in the following way: nn -a0 nngoback 3 The nn command will mark all articles in all groups as read (answer all to the catch-up question.) The following nngoback will then make the last three days of news unread again. Examples: nngoback 0 Mark the articles which have arrived today as unread. nngoback 1 Mark the articles which have arrived yesterday and today as unread. nngoback 6 Mark the articles which have arrived during the last week as unread. You cannot go more than 14 days back with nngoback. (You can change this limit as described below.) THE BACK_ACT DAEMON It is a prerequisite for the use of nngoback that the script back_act is executed at an appropriate time once (and only once) every day. Preferably this is done by cron right before the bacth of news for `today' is received. back_act will maintain copies of the active file for the last 14 days. Optionally, the back_act program accepts a single numerical argument specifying how many copies of the active file it should maintain. This is useful if news is expired after 7 days, in which case keeping more than 7 days of active file copies is wasteful. FILES
~/.newsrc The record of read articles. ~/.newsrc.goback The original rc file before goback. $db/active.N The N days `old' active file. $master/back_act Script run by cron to maintain old active files. SEE ALSO
nn(1), nncheck(1), nngrab(1), nngrep(1), nnpost(1), nntidy(1) nnadmin(1M), nnusage(1M), nnmaster(8) NOTES
nngoback does not check the age of the `old' active files; it will blindly believe that active.0 was created today, and that active.7 is really seven days old! Therefore, the back_act script should be run once and only once every day for nngoback to work properly. The days are counted relative to the time the active files were copied. AUTHOR
Kim F. Storm, Texas Instruments A/S, Denmark E-mail: storm@texas.dk 4th Berkeley Distribution Release 6.6 NNGOBACK(1)
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