A symbolic link is a special file that points to another file, i.e.
lrwxrwxrwx 1 root root 4 Jun 23 2007 awk -> gawk*
Delete gawk, and awk points nowhere - and won't work. Delete awk, and nothing at all happens to gawk.
A hard link is simply a file that points to the same inode as another. In effect, it's just another way of referring to the same file. You can't tell by looking at it that it's a hard link, and if you delete it - or the file it's linked to - nothing happens to the other file. The only clue you've got is by looking at the link count, that column in 'ls -l' that nobody knows what it is:
-rwxr-xr-x 3 root root 62872 Jan 14 14:06 gunzip
-rwxr-xr-x 3 root root 62872 Jan 14 14:06 gzip
-rwxr-xr-x 3 root root 62872 Jan 14 14:06 zcat
Each has a link count of 3. That means that there are three different files sharing the same inode number. And, sure enough:
[root@dg bin]# ls -i *z*
319701 gunzip 319701 gzip 319701 zcat
So why have three 'identical' files with different names? Well, here's what I do with one of my scripts.
[root@dg scripts]# ls -lai start*
1357990 -rwxr-xr-x 3 root root 446 Jan 28 16:44 start
1357990 -rwxr-xr-x 3 root root 446 Jan 28 16:44 start_this
1357990 -rwxr-xr-x 3 root root 446 Jan 28 16:44 start_that
Same file, hard linked.
#!/bin/bash
ECHO="/bin/echo"
MAIL="/bin/mail"
CALLED_NAME="`basename $0`"
case $CALLED_NAME in
start_this)
ICDIR="/thisdir"
;;
start_that)
ICDIR="/thatdir"
;;
*)
ICDIR="/theotherdir"
;;
esac
cd $ICDIR||{ $ECHO "$0 failed chdir"|$MAIL tim;exit 1; }
/usr/local/bin/icrun
ECHO="/bin/echo"
MAIL="/bin/mail"
CALLED_NAME="`basename $0`"
case $CALLED_NAME in
start_this)
ICDIR="/thisdir"
;;
start_that)
ICDIR="/thatdir"
;;
*)
ICDIR="/theotherdir"
;;
esac
cd $ICDIR||{ $ECHO "$0 failed chdir"|$MAIL tim;exit 1; }
/usr/local/bin/icrun
So all I do is see how it's called, and operate accordingly.
I believe that in dg/ux, cp was a hard link to mv.
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