UNIX for Dummies Questions & Answers

#!/bin/ksh
IAm=${0##*/}
if [ $# -ne 1 ]
then    printf "Usage: %s starting_HH:MM\n" "$IAm" >&2
        exit 1 
fi
# Verification that $1 is in proper format is left as an excercise for the user
HH=${1%:*}                                              # Get Hour from $1
MM=${1#*:}                                              # Get Minute from $1
HH=${HH#0}                                              # Strip HH leading 0
MM=${MM#0}                                              # Strip MM leading 0
M1=$(( (MM + 1) % 60))                                  # Calculate MM+1
M2=$(( (MM + 2) % 60))                                  # Calculate MM+2
H1=$(( (HH + (M1 < MM)) % 24))                          # Calc HH for MM+1
H2=$(( (HH + (M2 < MM)) % 24))                          # Calc HH for MM+2
HM=$(printf "%02d:%02d" "$HH" "$MM")                    # Format HH:MM
HM1=$(printf "%02d:%02d" "$H1" "$M1")                   # Format HH:MM for MM+1
HM2=$(printf "%02d:%02d" "$H2" "$M2")                   # Format HH:MM for MM+2
T0ERE=$(printf "%s:0[1-9]|%s:[1-5][0-9]" "$HM" "$HM")   # ERE for MM
T12ERE=$(printf "(%s|%s):[0-5][0-9]" "$HM1" "$HM2")     # ERE for MM+1 and MM+2
TERE=$(printf "(%s|%s)" "$T0ERE" "$T12ERE")             # ERE for MM to MM+2
# final ERE for color before or after desired timestamps
ERE=$(printf "(yellow.*%s|%s.*yellow)" "$TERE" "$TERE")
grep -E "$ERE" out.log

yellow team won at 00:23:59 on monday
red team won at 00:00:43 on monday
yellow team won at 00:01:07 on monday
yellow team won at 00:02:55 on monday
yellow team won at 23:59:23 on monday

at 00:23:59 on monday, yellow team won
at 00:00:43 on monday, red team won
at 00:01:07 on monday, yellow team won
at 00:02:55 on monday, yellow team won
at 23:59:23 on monday, yellow team won

./script_name 23:59

yellow team won at 00:01:07 on monday
yellow team won at 23:59:23 on monday
at 00:01:07 on monday, yellow team won
at 23:59:23 on monday, yellow team won