Sed command - help me understand

Shell Programming and Scripting
1

Hello,
can someone please explain me what the following commands do.. i know the output but i would like to understand the break down of what they do step by step.

1) sed -n "/ $(date +\%R -d "-1 min")/,$"p req.txt| wc -l

2)
awk '/19:00/,/22:00/' app.log |grep "mytesturl"|grep ',900,'|awk -F, '{print $1, $6, $10}' | awk '{print $2}'|sed -r 's/:[0-9][0-9]\.[0-9]{3}//g' |sort |uniq -c

i really appreciate the help..

2
  1. This will give the current time minus 1 min in the form of hh:mm
date +%R -d "-1 min"

This will print the lines begining (line that matches the above hh:mm time) till the end of the line for the file req.txt

sed -n "/ $(date +\%R -d "-1 min")/,$"p req.txt

This will count the no of lines returned

 wc -l

so

sed -n "/ $(date +\%R -d "-1 min")/,$"p req.txt| wc -l

will o/p no of lines.

  1. This will print lines between the lines that matches 19:00 and till 22:00
awk '/19:00/,/22:00/' app.log

From the above lines, it will filter only the lines that contain the string mytesturl

awk '/19:00/,/22:00/' app.log |grep "mytesturl"

From the returned lines, this will print field no 1,6 and 10 only which are comma seperated

awk '/19:00/,/22:00/' app.log |grep "mytesturl"|grep ',900,'|awk -F, '{print $1, $6, $10}'

This will print only field 2 from the above lines

awk '/19:00/,/22:00/' app.log |grep "mytesturl"|grep ',900,'|awk -F, '{print $1, $6, $10}' | awk '{print $2}'

The sed command and sort and uniq:
sed will look for string like :hh.mmm and replace with nothing and its o/p is sorted and then count on the uniq values

3

this was a very good explanation...