tail

Output appended data as the file grows:

tail -f /etc/httpd/logs/error_log

Compress

From View compressed .gz files without uncompressing using Z commands

To view compressed log files:

# -f compressed and uncompressed
zcat -f dmesg | more

# no need for -f
zless dmesg.1.gz
zmore dmesg.1.gz

# -i case insensitive
zgrep -i usb dmesg.1.gz | more

# diff
zcmp dmesg.1.gz dmesg.2.gz
zdiff dmesg.1.gz dmesg.2.gz | more

Last x Lines

Last 30 lines of catalina.out:

tail -n30 /opt/tomcat5/logs/catalina.out

Long Lines

Tail a log file with long lines truncated:

tail -f logfile.log | cut -b 1-80

Also useful for looking at different parts of the line, e.g. cut -b 50-100 shows columns 50 through 100.

Or even smarter, use tput cols to tell you the width of the terminal:

tail -f logfile.log | cut -b -$(tput cols)