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OR'ing condition in script

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# 8  
Old 04-20-2005
Quote:
Originally Posted by Just Ice
however, i've never really used the "-f" option --- like most other esoteric options of other commands that are good to know but not required for basic stuff --- so i don't actually understand the unlink statement ... maybe one of the hardcore c programmers here can explain it better ...
Consider this:
Code:
$ date > one
$ touch two
$ chmod 0 two
$ cp one two
cp: cannot open 'two': Permission denied
$ cp -f one two

With the first cp, I could not open "two" for writing (could not obtain a file descriptor). By unlinking "two", the second cp command created a new "two" from scratch. However, the language you quoted implied that cp would first try to open the destination file and if that worked, bypass the unlink. More normal language is:
Quote:
Force existing destination pathnames to be removed before copying, without prompting for confirmation. This option has the effect of destroying and replacing any existing file whose name and directory location conflicts with the name and location of the new file created by the copy operation.
And that could cause a different result. The above language came from HP-UX. What OS supplied your language?
# 9  
Old 04-20-2005
Solaris 8 ...
# 10  
Old 04-21-2005
Oh my...

You're right. Solaris does say that! I just tried the sequence
touch three
ln -s three two
date > one
cp -f one two
on both Solaris and HP-UX. On HP-UX, I get a brand new file called "two" and "three" is untouched. On Solaris, three is overwritten. Smilie

And I just checked the posix standard. According to the standard, Solaris has it right and HP-UX has it wrong.
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