develooper Front page | perl.beginners | Postings from April 2002

Re: Serious problem with perl -pi -e

Thread Previous | Thread Next
From:
drieux
Date:
April 30, 2002 10:00
Subject:
Re: Serious problem with perl -pi -e
Message ID:
AEF681C2-5C5B-11D6-9C26-0030654D3CAE@wetware.com

On Monday, April 29, 2002, at 10:13 , sharan wrote:
[..]

first off note that chmod 400 did not take you where you expected.
> sharan@SHARAN ~
> $ ll foo
> -r--r--r--    1 sharan   None            4 Apr 30 10:39 foo

ls -l foo
-rw-r--r--  1 drieux  wheel  4 Apr 30 09:54 foo
[jeeves:/tmp/drieux] drieux% chmod 400 !$
chmod 400 foo
[jeeves:/tmp/drieux] drieux% !l
ls -l foo
-r--------  1 drieux  wheel  4 Apr 30 09:54 foo
[jeeves:/tmp/drieux] drieux%

>
> sharan@SHARAN ~
> $ perl -pi -e 's/o/e/' foo
> Can't do inplace edit on foo: Permission denied.

so while your version of a filesystem is near to a
traditional model.... it seems to be 'off a peg'.

>
> sharan@SHARAN ~
> $ cat foo
> cat: foo: No such file or directory

the short skid is that the 'pie' trick is writing to a
tmp file 'unspecified' here - and then moving that file back.

the alternative is to specify a tmp file extension...

gax: 61:] perl -pi'.bob'  -e 's/o/e/' foo
gax: 62:] ls -ltr
total 12
-rw-r--r--    1 drieux   house          28 Apr 28 08:08 file
-r--------    1 drieux   house           4 Apr 30 08:57 foo.bob
-r--------    1 drieux   house           4 Apr 30 08:58 foo
gax: 63:] diff foo foo.bob
1c1
< fee
---
 > feo
gax: 64:]


perldoc perlrun - and you will notice that there is the
interesting bit about

         For a discussion of issues surrounding file permis-
             sions and -i, see the Why does Perl let me delete
             read-only files? Why does -i clobber protected files?
             Isn't this a bug in Perl? entry in the perlfaq5 man-
             page.

which would be found with

	perldoc perlfaq5

or with

	perldoc -q "-i"

or skip straight ahead to

This is elaborately and painstakingly described in the
        "Far More Than You Ever Wanted To Know" in
        http://www.perl.com/CPAN/doc/FMTEYEWTK/file-dir-perms .


which will take you off on a wild adventure.

or:


        The executive summary: learn how your filesystem works.
        The permissions on a file say what can happen to the data
        in that file.  The permissions on a directory say what can
        happen to the list of files in that directory.  If you
        delete a file, you're removing its name from the directory
        (so the operation depends on the permissions of the direc-
        tory, not of the file).  If you try to write to the file,
        the permissions of the file govern whether you're allowed
        to.







ciao
drieux

---


Thread Previous | Thread Next


nntp.perl.org: Perl Programming lists via nntp and http.
Comments to Ask Bjørn Hansen at ask@perl.org | Group listing | About