[Courses][Linux comands] Finding things with locate, find, and grep

[lc-Kurse at LuftHans.com]

Am 23. Feb, 2004 schwätzte Peter Clay so:

> (warning: this is pedantic and not nearly as readable as Carla's original
> post)

Mine's pretty pedantic as well, but I really want to know if I'm overlooking
something :).

> Now is probably a good time to mention that find can be both useful and
> dangerous in conjunction with xargs:
>
> pete at platinum:~/t$ touch wanted
> pete at platinum:~/t$ touch junk.png
> pete at platinum:~/t$ touch 'wanted junk.png'
> pete at platinum:~/t$ ls -l
> -rw-rw-r--    1 pete     pete          0 Feb 23 09:59 junk
> -rw-rw-r--    1 pete     pete          0 Feb 23 09:59 wanted
> -rw-rw-r--    1 pete     pete          0 Feb 23 09:59 wanted junk.png
> pete at platinum:~/t$ find . -name '*.png' | xargs rm
> rm: cannot remove `junk.png': No such file or directory
> pete at platinum:~/t$ # huh?
> pete at platinum:~/t$ ls -l
> -rw-rw-r--    1 pete     pete          0 Feb 23 09:59 wanted junk.png

lufthans at fs:/tmp/fred$ touch wanted
lufthans at fs:/tmp/fred$ touch junk.png
lufthans at fs:/tmp/fred$ touch 'wanted junk.png'
lufthans at fs:/tmp/fred$ ls -l
insgesamt 0
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:43 junk.png
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:43 wanted
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:43 wanted junk.png
lufthans at fs:/tmp/fred$ find . -name \*.png -exec rm {} \;
lufthans at fs:/tmp/fred$ ls -l
insgesamt 0
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:43 wanted

"\*.png" and "'*.png'" are functionally equivalent.

> In trying to locate and delete all my .png files, I've deleted something
> accidentally (wanted) and not deleted something I wanted to delete ("wanted
> junk.png"). UNIX allows spaces in filenames but doesn't always handle them
> sensibly. GNU find allows you to dodge this landmine:
>
> pete at platinum:~/t$ find . -name '*.png' -print0 | xargs -0 rm
>
> That command uses null characters as seperators rather than spaces.
> For extra bonus security holes, you can put newlines in filenames and
> cause mayhem for other people's find commands. For example, it used to be
> common to have a cron job to remove 'core' files nightly, something of the
> form:
>
> find / -name core | xargs rm
>
> .. running from root's crontab. It is possible to construct some filenames
> which will cause that command to remove e.g. /etc/passwd, preventing
> anyone from logging into the system. I'm going to leave it as an exercise
> for the reader in how to do that.

lufthans at fs:/tmp/fred$ touch wanted
lufthans at fs:/tmp/fred$ touch junk.png
lufthans at fs:/tmp/fred$ touch 'wanted junk.png'
lufthans at fs:/tmp/fred$ touch 'wanted
> junk.png'
lufthans at fs:/tmp/fred$ ls -lb
insgesamt 0
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:46 junk.png
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:46 wanted
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:46 wanted\ junk.png
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:46 wanted\njunk.png
lufthans at fs:/tmp/fred$ find . -name \*.png -exec rm {} \;
lufthans at fs:/tmp/fred$ ls -lb
insgesamt 0
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:46 wanted


lufthans at fs:/tmp/fred$ touch wanted
lufthans at fs:/tmp/fred$ touch junk.png
lufthans at fs:/tmp/fred$ touch 'wanted junk.png'
lufthans at fs:/tmp/fred$ touch 'wanted
junk.png'
lufthans at fs:/tmp/fred$ ls -lb
insgesamt 0
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:48 junk.png
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:48 wanted
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:48 wanted\ junk.png
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:49 wanted\njunk.png
lufthans at fs:/tmp/fred$ find . -name w\*junk.png -exec rm {} \;
lufthans at fs:/tmp/fred$ ls -lb
insgesamt 0
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:48 junk.png
-rw-r--r--    1 lufthans lufthans        0 2004-02-24 01:48 wanted

Am I overlooking anything?

ciao,

der.hans
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