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Help with these unix commands!


 
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# 1  
Old 03-02-2007
Help with these unix commands!

Hi to all,

I have just started to learn Unix, and am having problems trying to understand the following two unix commands. if any1 could help i would greatly appreciate it.

1) ls -s | sort -nr | head -3

2) man -k c | grep -i ' c* ' | grep 1

i understand that for 1) the command will locate the file and not the contents of the file. for 2) i understand that the command is to do with the unix manual.

as you can see i am a beginner.

thanks in advance
vish
# 2  
Old 03-02-2007
The best shot will be to check the man pages for "man, head, ls, grep, sort" and their respective parameters. Also, you can execute the commands in your shell, this will answer your questions best.
# 3  
Old 03-02-2007
man -k "KEYWORD" #List all man pages that is same as that of of KEYWORD

Probably the commands that you posted might beprinting all all man "KEYWORD" pages in man section (1).
# 4  
Old 03-04-2007
Quote:
Originally Posted by Vn3050
Hi to all,

I have just started to learn Unix, and am having problems trying to understand the following two unix commands. if any1 could help i would greatly appreciate it.

1) ls -s | sort -nr | head -3
Code:
ls -s  |  ## print the filenames in the current directory preceded by the size in blocks
sort -nr |  ## sort the output numerically in reverse order
head -3  ## print the first three lines

In other words, show the sizes and filenames of the 3 largest files in the current directory.

Quote:
2) man -k c | grep -i ' c* ' | grep 1
Code:
man -k c |  ## print the commands whose names and descriptions contain the letter c
grep -i ' c* ' | ## search for output lines which contina an upper or lowercase "c"
grep 1 ## print only lines found by the previous grep which contain the number 1


Quote:
i understand that for 1) the command will locate the file and not the contents of the file. for 2) i understand that the command is to do with the unix manual.

as you can see i am a beginner.

thanks in advance
vish
# 5  
Old 03-04-2007
Quote:
Code:
grep -i ' c* ' | ## search for output lines which contains an upper or lowercase "c"

Actually that is not correct, as written here and in the original post it will match any lines in which the input contains two spaces, the 'c' is rendered pointless by the use of *. This is a typical example of an 'excessively greedy' regular expression.

Last edited by reborg; 03-05-2007 at 07:59 PM.. Reason: correct an inaccuracy, two spaces, not one.
# 6  
Old 03-05-2007
Quote:
Originally Posted by reborg
Code:
grep -i ' c* ' | ## search for output lines which contains an upper or lowercase "c"

Actually that is not correct, as written here and in the original post it will match any lines in which the input contains a space, the 'c' is rendered pointless by the use of *. This is a typical example of an 'excessively greedy' regular expression.
Quite right. It actually matches any line which contains two spaces separated by zero or more upper or lower case Cs.
# 7  
Old 03-05-2007
thanks for all your help!

i am also stuck on the following question, but after learning a bit more unix. i have written an answer to it. Can anyone check to see if it is correct and what improvements need to be made?

Question:

Write a pipeline that updates the content of a file (a file of your choice) by replacing all matches of the word ‘and' with the symbol ‘&' and by replacing the end of each line with the user login name. If the command completes successfully it should print ‘YES', otherwise it should print ‘NO'.

Answer:

cat text.txt | sed -e s/and/$USER/g -e s/$/”&”/g | cat -> text.txt
&& echo yes || echo no

thanks
 

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