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Full Discussion: Shell ${1:-/etc/hosts} meaning
Operating Systems Linux Shell ${1:-/etc/hosts} meaning Post 302834569 by Don Cragun on Friday 19th of July 2013 09:10:39 AM
Old 07-19-2013
If no arguments are passed to this script or if the 1st argument passed to this script is an empty string, the shell variable filename will be set to "/etc/hosts"; otherwise the 1st argument passed to the script will be assigned to filename.

So, if your script is named some and you invoke it as:
Code:
./some
    or as
./some ""

then filename will be set to /etc/hosts, but if you invoke it as:
Code:
./some /etc/motd

then filename will be set to /etc/motd.
These 2 Users Gave Thanks to Don Cragun For This Post:
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LEARN ABOUT LINUX

motd.tail

MOTD.TAIL(5)						   Debian Administrator's Manual					      MOTD.TAIL(5)

NAME

       motd.tail - Template for building the system message of the day

DESCRIPTION

       On Debian systems, the system message of the day is rebuilt at each startup, in order to display an accurate information. /etc/motd.tail is
       the file to edit permanent changes to the message of the day.

OVERVIEW

       The initiation script /etc/init.d/bootmisc.sh prepends a line containing information about the system  to  /etc/motd.tail  and  stores  the
       resulting  file in /var/run/motd. /etc/motd is a symbolic link to /var/run/motd.  This is done to prevent changes to /etc as the system can
       not assume /etc to be writable.

       Changes to /etc/motd effectively end up in a file under /var/run which will be regenerated upon reboot.

       A symbolic link to a different file, such as /etc/motd.static disables this behaviour.

FILES

       /etc/init.d/bootmisc.sh
	      The initiation script which builds /var/run/motd

       /etc/motd
	      Symbolic link to the system message of the day at /var/run/motd

       /etc/motd.tail
	      Template for building the system message of the day

       /var/run/motd
	      System message of the day file rebuilt at each computer start

SEE ALSO

       login(1), issue(5), motd(5).

Debian								    2007-04-28							      MOTD.TAIL(5)
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