Shell Programming and Scripting

Well, yes. As Perderabo said, for a large number of files, the 'find | xargs' won't work - definitely not for your 47GB of files. Use mahendramahendr's perl script to do the job for you.

Code:

#! /usr/bin/ksh

touch -t $(($(date "+%Y") + 1))$(date "+%m%d%H%M") notfound
OLDEST=notfound
find . -type f | while read f ; do
        [[ $f -ot $OLDEST ]] && OLDEST=$f
done
echo oldest file is $OLDEST
rm notfound
exit 0

Hi,

I found the perl script helpful, thanks for posting it. However, I think there is one small bug in it.

I think it should be
($mn,$hr,$day,$mnth,$year)=...

$ perldoc -f localtime
localtime EXPR
localtime
Converts a time as returned by the time function to a 9-element
list with the time analyzed for the local time zone. Typically
used as follows:

# 0 1 2 3 4 5 6 7 8
($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
localtime(time);
[...]

in all the subdirectories...

find . -type f -printf "%T@ %p \n" | sort -n -k 1,1 | awk '{print $2}'

Tim

Here is a perl script that I wrote for some commercial radio stations that want to delete the oldest archive file out of subdirectories from a root directory...

Code:

#!/usr/bin/perl

# This will sort all the files in various subdirectories by creation date.
# find . -type f -printf "%T@ %p \n" | sort -n -k 1,1 | awk '{print $2}'

$ls = "/usr/bin/find";
$df = "/bin/df -k";
$grep = "/bin/grep";
$lookfor = "*.mp3";
$dir = "/usr/local/public/archive/";
$percent = 95;

$fullfile = $dir . $lookfor;

open(LS_T, "$ls $dir -type f -printf '%T@ %p \n' | /usr/bin/sort -n -k 1,1 | /usr/bin/awk '{print \$2}'|") or die "Can't do $ls";
$i=0;
while(<LS_T>){
        chop;
        $filename = $_;
        $result=`$df $dir | $grep -v Filesystem`;
        chop $result;
        $_ = $result;
        tr/ / /s;
        ($fs,$kbytes,$used,$avail,$percentused,$mountedon) = split / /;
        chop $percentused;
        if ($percentused >= $percent){
                print "deleting \'$filename\'\n";
                `rm "$filename"`;
                $i++;
        } else {
                exit;
        }
}

Ok... Found a bug soon as I posted this. In the previous example the "awk" will only print out the string after the number up to the end of the line or another space. Not good if you have files or directories with spaces. This would work better.

Code:

find . -type f -printf "%T@ %p \n" | sort -n -k 1,1 | sed 's/^[0-9]* //'

I would use the following command (assuming I had GNU find available):

find $DIR -printf "%T@ %p\n" | sort -n | head -1

The %T is modification time in a custom format; @ is the format specifier for for "seconds since the epoch. The rest should be pretty self-evident. %C would be used if you cared about the "ctime" (the time at which the file's inode was changed in any way, including modifications to the file contents (as with mtime) but also changes to ownership, permissions, link count? etc.

A couple of heuristics for scripting in general:

Any time you're trying to find files with specific characteristics other than matching a simple glob pattern and any of the simple test features like -d (directory) or -r (readable), etc, you almost always want to use the find command. Most of the switches and arguments to find control what find will consider returning (to things like -print, -exec, or -ls).

Any time you're going to compare or manipulate timestamps under UNIX you probably want to use "seconds since the epoch" (this allows simple numeric operations such as sorting or arithmetic adjustment).

So it seems obvious to just traverse the tree printing all the timestamps in a usable form; sort numerically and discard all but the first line. (You could also sort -nr, reversed, and take the last line with tail -1; but then your tail process has to read the entire pipe. In this example the head command can exit and break the pipe to kill to output from the sort command; which is marginally more efficient. Of course all of the expense in this is in the sort command ... it will take most of the CPU time and memory. Meanwhile, of course the find command will expend I/O -- that's inherent in traversing a filesystem tree).

P.S. If you need to convert a "seconds since the epoch" timestamp into a form you can read you can use an expression like:

date --date "$(( $(date +%s) - $TIMESTAMP )) seconds ago"

.. and naturally you can also specify any format you like for that output as you would with any other date


JimD (former Linux Gazette AnswerGuy)