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Shell Programming and Scripting
want file to regenerate after deletion
Post 302354295 by Corona688 on Thursday 17th of September 2009 04:42:49 PM
09-17-2009
There's no fundamental-to-the-system way to make a file that ressurects itself. If you want to leave a file alone, the natural thing to do is to stop trashing it! 
And change file and directory permissions to prevent people from trashing it in the first place. I'm reminded of a story:
And change file and directory permissions to prevent people from trashing it in the first place. I'm reminded of a story:
Quote:
From: tzs@stein.u.washington.edu (Tim Smith)
Organization: University of Washington, Seattle
I was working on a line printer spooler, which lived in /etc. I wanted to remove it, and so issued the command "rm /etc/lpspl." There was only one problem. Out of habit, I typed "passwd" after "/etc/" and removed the password file. Oops.
I called up the person who handled backups, and he restored the password file.
A couple of days later, I did it again! This time, after he restored it, he made a link, /etc/safe_from_tim.
About a week later, I overwrote /etc/passwd, rather than removing it.
After he restored it again, he installed a daemon that kept a copy of /etc/passwd, on another file system, and automatically restored it if it appeared to have been damaged.
Fortunately, I finished my work on /etc/lpspl around this time, so we didn't have to see if I could find a way to wipe out a couple of filesystems...
Organization: University of Washington, Seattle
I was working on a line printer spooler, which lived in /etc. I wanted to remove it, and so issued the command "rm /etc/lpspl." There was only one problem. Out of habit, I typed "passwd" after "/etc/" and removed the password file. Oops.
I called up the person who handled backups, and he restored the password file.
A couple of days later, I did it again! This time, after he restored it, he made a link, /etc/safe_from_tim.
About a week later, I overwrote /etc/passwd, rather than removing it.
After he restored it again, he installed a daemon that kept a copy of /etc/passwd, on another file system, and automatically restored it if it appeared to have been damaged.
Fortunately, I finished my work on /etc/lpspl around this time, so we didn't have to see if I could find a way to wipe out a couple of filesystems...
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LEARN ABOUT NETBSD
newgrp
NEWGRP(1) BSD General Commands Manual NEWGRP(1) NAME
newgrp -- change to a new primary group SYNOPSIS
newgrp [-l] [group] DESCRIPTION
The newgrp command changes a user to a new primary group (real and effective group ID) by starting a new shell. The user remains logged in and the current directory and file creation mask remain unchanged. The user is always given a new shell even if the primary group change fails. The newgrp command accepts the following options: -l The environment is changed to what would be expected if the user actually logged in again. This simulates a full login. The group is a group name or non-negative numeric group ID from the group database. The real and effective group IDs are set to group or the group ID associated with the group name. If group is not specified, newgrp restores the user's real and effective group IDs to the user's primary group specified in the password database. The user's supplementary group IDs are restored to the set specified for the user in the group database. If the user is not a member of the specified group, and the group requires a password, the user will be prompted for the group password. FILES
/etc/group The group database /etc/master.passwd The user database /etc/passwd A Version 7 format password file EXIT STATUS
If a new shell is started the exit status is the exit status of the shell. Otherwise the exit status will be >0. SEE ALSO
csh(1), groups(1), login(1), sh(1), su(1), umask(2), group(5), passwd(5), environ(7) STANDARDS
The newgrp command conforms to IEEE Std 1003.1-2001 (``POSIX.1''). HISTORY
A newgrp command appeared in Version 6 AT&T UNIX. A newgrp command appeared in NetBSD 5.0. BUGS
There is no convenient way to enter a password into /etc/group. The use of group passwords is strongly discouraged since they are inherently insecure. It is not possible to stop users from obtaining the encrypted password from the group database. BSD
June 6, 2007 BSD