sed []

sed can be used to substitute
eg. substitute : with nothing, and do for every occurrence (represented by g)

sed 's/://g'

s/X/Y/
replaces X with Y
/ represents nothing
g represents every occurance

Below removed [ and ]

sed 's/[][]//g'

below removes , 7 and l

sed 's/[,7l]//g'

sed 's/.*[/]//'

For example, if you are trying to get the log format for apache (centos):

grep ^ErrorLog /etc/httpd/conf/httpd.conf | awk '{print $2}' | sed 's/.*[/]//'

Returns

error_log

Sometimes format is error.log