UNIX for Dummies Questions & Answers

I have a data file called "statistics.dat"

The first three lines are headers and the rest of the lines contain client id number followed by their statistical data.


For example,
line 1: 1 Header
line 2: 2 Header
line 3: 3 Header
line 4: 0801 9 10 2 1
line 5: 0802 7 11 4 6
.
line 18: 0890 2 6 9 12
.
.
line 30: 0930 14 8 4 9

I want to write a command string that will only display the first 3 lines and line 18.

This is what I have tried so far and it doesn't work:

head -3 statistics.dat | grep '0890'

I've also tried:

cat statistics.dat | head -3 | grep '0890'

I have tried lots of variations on the commands listed above but nothing seems to work. Can someone help me with this?

Am I using the right commands or are their other commands that I should be using?

When you do:
head -3 statistics.dat | grep '0890'
this selects the first 3 lines and does not display them, but instead forwards them (pipes) into the next command for processing, and of course the grep will not find that string in that set of lines.

If those header lines were very easy to identify, a single grep command with two search arguments could do it, such as:

grep -e Header -e "^0890" statistics.dat

If not, do two separate commands:

head -3 statistics.dat
grep "^0890" statistics.dat

The carat is anchoring its search to the very beginning of each line (which I think is correct for your data) so that it will not accidentally find the search string somewhere else in the line. Here is a script that you can execute with a parameter:

Code:

#!/bin/sh
client=${1?Need one parameter - the client ID}
head -3 statistics.dat
grep "^$client" statistics.dat
exit 0

Thanks Jimbo! for your help I now understand what the pipe "|" does. I was thinking that it was just used to separate the commands on the same line.I have to learn that there is more than just one way to write a command string that does the same thing.
I just got to carried away with that head command.

Thanks,

JJ

Great! unix probably just got a lot more fun for you. Speaking of separators, the semicolon separates multiple commands on the same line. And || and && are command separators like semicolon, but conditional. The former means do 2nd command only if the 1st has an error, and the latter means do 2nd command only if the 1st has no error. They are not pipes - output is not forwarded to the 2nd command.

Code:

badcommand || echo 'not a good command'
pwd && echo 'is where I currently am'