This document is the source code for the logrotate utility. It summarizes the logrotate program as rotating log files by compressing or removing old log files based on options in a configuration file. Key sections of code handle parsing command line arguments, reading options from a configuration file, and implementing the core rotation logic on individual log files.

1. #!/bin/bash
# logrotate - rotate log files
# Copyright 2001, Chris F.A. Johnson
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2, or (at your option)
# any later version.
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details:
# http://www.gnu.org/copyleft/gpl.html
usage()
{
if [ -n "$1" ]
then
echo " $progname: $*"
else
echo " $progname - rotate log files"
fi
if [ $verbose -eq 1 ]
then
echo "
LogRotate is a log rotation script. Run this from cron on a
periodic basis (daily, weekly, monthly) etc.
"
fi
echo " USAGE: $progname [OPTIONS] [log-control-file]
OPTIONS:
-c ZIP - use ZIP (gzip or bzip2) to compress rotated files
-d DIR - place rotated files in directory DIR
-f FILE - rotate FILE; do not use a control file
-k N - keep last N lines of the logfile
-n N - keep N log files (default 5)
The above options do not override options in a control file unless:
-o - override control file options"
if [ $verbose -eq 0 ]
then
echo "
-h - help: print this message
-H - help: print more detailed message"
else
echo "
-h - help: print shorter message
-H - help: print this message"
fi
echo " -v - verbose:
-V - print version information
"
if [ $verbose -eq 1 ]
then

2. echo " If no control file is given, $progname looks for
./.logrotate.conf then $HOME/.logrotate.conf then
/etc/logrotate.conf, and uses the first one it finds.
The log-control-file is a text file containing a list of log files
to rotate, wherein each entry is on a separate line and each entry
contains the name (absolute or relative path: see NOTE) of the log file that
needs to be rotated.
Each line may also contain options, separated by tabs:
dir=D - put rotated files in directory D.
The name of the logfile is expanded to the full path
and the slashes are changed to dashes.
files=N - keep N log files
keep=N - keep the last N lines in the file
(This leaves them in the rotated file as well;
I may change the behaviour to remove them from
the rotated file, or add an option to do that.)
gzip
bzip2 - compress the log files with gzip or bzip2
size=N - do not rotate if the file is less than N bytes or lines
N is an integer optionally ending with a letter:
B - bytes (default)
K - append 000 to the number
M - append 000000 to the number
G - append 000000000 to the number
L - refer to number of lines rather than bytes
# --- sample .logrotate.conf ---
# Filename = /var/log/foo
# Compress with gzip
# Maximum number of rotated files = 5
# Keep the last 25 lines of the log file
# Don't rotate if the log file contains fewer than 15,000 lines
/var/log/foo gzip files=5 keep=25 size=15000L
# Filename = ./mylog
# All the defaults are used
mylog
# ---- end .logrotate.conf ----
NOTE: Files in $HOME/.logrotate.conf and /etc/logrotate.conf
should be absolute paths, since the working directory
could be anywhere (unless a file of a certain name should
be rotated wherever it is found)."
fi
echo "
Copyright 2001, Chris F.A. Johnson
Please send corrections, improvements, bugs reports, suggestions,
etc., to cfaj@freeshell.org
Logrotate is derived from a script by javadesigner@yahoo.com
with modifications by Heiner Steven, but there is very
little of the original code left.

3. This script may be copied under the terms of the
GNU General Public License"
}
fullpath()
{
filename=${1##*/}
dirname=${1%/*}
( cd "$dirname" && echo "`pwd`/$filename" )
}
die()
{
echo "$progname: $*" >&2
exit 1
}
rotateOneFile()
{
logfile=$1
if [ -n "$savedir" ]
then
savelog="$savedir/`fullpath $logfile | tr '/' '-'`"
else
savelog=$logfile
fi
i=${maxno:-$default_maxno}
while [ $i -ge 1 ]
do
newname="$savelog.$i$suffix"
i=$(( $i - 1 ))
oldlogfile=$savelog.$i$suffix
if [ -r "$oldlogfile" ]
then
mv -f "$oldlogfile" "$newname" || die "Could not move "$oldlogfile"
to "$newname""
if [ $verbose -ge 1 ]
then
echo ""$oldlogfile" --> "$newname""
fi
fi
done
newlogfile="$savelog.0"
mv "$logfile" "$newlogfile" || die "Could not move "$logfile"
to "$newlogfile""
if [ $verbose -ge 1 ]
then
echo ""$logfile" --> "$newlogfile""
fi
if [ $keep -gt 0 ]
then
tail -$keep "$newlogfile" > "$logfile"
else
> $logfile
fi
if [ "$compress" ]
then
rm -f "$newlogfile$suffix"
$compress $OPT "$newlogfile"

4. fi
return 0
}
version()
{
echo $version
}
verbose=0
longusage=0
version="0.5"
copyright=2001
author="Chris F.A. Johnson"
progname=${0##*/}
TAB=`printf "t"`
default_maxno=5
override=0
keep=0
suffix=
compress=
filename=
savedir=
while getopts :vVhHf:n:c:k:od: var
do
case "$var" in
c) compress=$OPTARG ;;
d) savedir=$OPTARG ;;
f) logfile=$OPTARG ;;
k) keep=$OPTARG ;;
n) maxno=$OPTARG ;;
o) override=1 ;;
h) usage; exit ;;
H) verbose=$(( verbose + 1 )); usage; exit ;;
v) verbose=$(( verbose + 1 )) ## allow levels of verbosity
OPT="-v"
;;
V) version; exit ;;
*) usage "Illegal option -- $OPTARG" >&2
exit 1
;;
esac
done
shift $(( $OPTIND - 1 ))
if [ $verbose -eq 3 ]
then
set -x
fi
RETURN=0
if [ -n "$filename" ]
then
if [ -r "$filename" ]
then
rotateOneFile "$filename"
elif [ -f "$filename" ]
then
echo "$progname: "$filename" is not readable" >&2

5. RETURN=1
else
echo "$progname: "$filename" not found" >&2
RETURN=1
fi
exit $RETURN
fi
if [ $# -eq 0 ]
then
if [ -r ./.logrotate.conf ]
then
controlfile=./.logrotate.conf
elif [ -r $HOME/.logrotate.conf ]
then
controlfile=HOME/.logrotate.conf
elif [ -r /etc/logrotate.conf ]
then
controlfile=/etc/logrotate.conf
else
echo "$progname: could not find a control file" >&2
exit 1
fi
fi
if [ $verbose -ge 1 ]
then
echo "Using ${controlfile}"
fi
IFS=$TAB
while read filename options
do
case "$filename" in
[^/a-zA-Z0-9]#*|#*|"") continue ;; ## skip comments & empty lines
esac
if [ $verbose -ge 1 ]
then
echo "FILE: $filename"
if [ $verbose -ge 2 ]
then
echo "OPTIONS: $options"
fi
fi
[ -f "$filename" ] || { # ignore non-existent files
if [ $verbose -ge 1 ]
then
echo "$filename not found" >&2
fi
continue
}
if [ $override -eq 0 ]
then
suffix=
compress=
units=
savedir=
size=0
filesize=0
keep=0
maxno=$default_maxno

6. for opt in $options
do
if [ $verbose -ge 1 ]
then
echo $opt
fi
case $opt in
files=*) maxno=${opt#*=}
;;
keep=*) keep=${opt#*=}
;;
gzip) compress=gzip
suffix=".gz"
;;
bzip2) compress=bzip2
suffix=".bz2"
;;
dir=*) savedir=${opt#*=}
;;
size=*) size="${opt#*=}"
units=bytes
if [ "`uname`" = "SunOS" ]
then
SUN="-g"
else
SUN=""
fi
filesize=`ls -l $SUN $filename | {
IFS=" "
read a b c d size f
echo $size
}`
case $size in
[0-9]*B) size="${size%B}" ;;
[0-9]*K) size="${size%K}000" ;;
[0-9]*M) size="${size%M}000000" ;;
[0-9]*G) size="${size%G}000000000" ;;
[0-9]*L) size="${size%L}"
filesize=$(( `wc -l < $filename` + 0 ))
units=lines
;;
esac
if [ $filesize -lt $size ]
then
if [ $verbose -ge 1 ]
then
echo "Skipping $filename ($filesize < ${size%[A-Za-z]})"
fi
continue 2
else
if [ $verbose -ge 1 ]
then
echo "$filename ( ${filesize#[ ]} >= $size
$units )"
fi
fi
;;
esac
done
fi
if [ $verbose -ge 1 ]
then

7. if [ -n "$compress" ]
then
echo "Compression enabled, using $compress"
fi
fi
rotateOneFile "$filename"
done < "$controlfile"