2001.10_Command Line Tools-Locate Find.pdf

PROGRAMMING

COMMAND

Locate and Find

COMMAND

COLIN MURPHY

There are many

branches in a UNIX-

type file system, so it

will come as no

surprise to you when

you realise that you

have forgotten on

which twiglet you have

left a now desperately

sought after file.

Even if you have an infallible memory you may

still have to deal with an unfamiliar landscape,

different distributions have different file layouts,

which will only frustrate you when you are trying to

find a system file – the XF86Config file is a good

example of this. Thankfully, there are a number of

tools and utilities that can help you find the files

you need.

Most Linux distributions will come with the locate

utility, which will give you the location of any files

that have the text you are looking for in their

filenames. So the command:

based on other criteria like file size or by the date

the file was last modified. This is a feature-rich

and powerful command made obvious because

the manpage is so big. The basic thing to

remember when calling ‘find’ is that you need to

provide the search criteria as well as the search

pattern, so the command:

[root@localhost /]$ find /var/log/ -name U

‘*.log’

will give me

colin@localhost colin]$ locate XF86Config

/var/log/security.log

/var/log/auth.log

/var.log/user.log

will give me

/etc/X11/XF86Config

/etc/X11/XF86Config.old

/etc/X11/XF86Config.test

/usr/X11R6/lib/X11/XF86Config-4.eg

/usr/X11R6/man/man5/XF86Config.5x.bz2

amongst many other files. Breaking this down – we

will only look in the /var/log directory and any

directories below it. We are basing our search

criteria on the names of files only and that we only

want to know about filenames that end in “.log”.

There are many search criteria other than -name ,

all of which are listed in the manpages, here are

just some:

Crond

showing me all the files that have the text

‘XF86Config’ in the filename, some of which I

really should get around to deleting the next time

I do some tidying up! If you have some idea of

the filename then locate will help you track down

its location.

locate relies upon its own database, which, to be

of any use, needs to be updated regularly. If you are

in the habit of leaving your machine on overnight

then this usually will happen automatically when

the nightly crond jobs are run. If your machine is

never on late enough for these jobs to run then you

will need to run the updatedb command yourself at

some point – maybe as you log out, something

which could be automated by adding the command

to your ~/.bash_logout file in your home directory.

The advantage of having locate use a database

means queries will be answered very quickly, the

disadvantage is the database will be out of date,

especially if you have been creating or copying a lot

of files in one session, even this can be solved by

running updatedb from the command line, leaving

you with time to go get a coffee.

find is another command line tool that will help

you find files, but this time you can search for files

Crond is the batch daemon

which starts other processes

at predetermined times,

which are described in the

control file etc/crontab.

-mmin -n allows you to look for files that were

modified no less that n minutes ago – useful if

you wanted to see which log files had just been

written to. +n would allow you to look for files

that are older than n minutes.

-size +n will look for files that are bigger than n in

512 byte sized blocks. Put a “c” after the value

to search for byte counts or a “k” to search for

kilobyte counts,

-user name will allow you to look for files that

only belong to the named user.

Bash logout

The search criteria can by combined to make for a

more powerful search, so

#/.bash_logout is one of the

bash shell command files, this

one being run when you exit

from a bash shell session,

usually when you are shutting

the machine down to turn it off.

[root@localhost /]$ find -mmin -30 -user colin

will only tell me about files that have been

modified in the last half an hour and only belong to

the user colin.

53 LINUX MAGAZINE 13 · 2001

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