Shell Programming and Scripting

Hello Guys !

i'm new to shell so please if anyone could explain the following things in detail

1> F"[,.?\! ]" why we used it? and what all these sign (,.?\!) means here can we add more?
2> what are the two for loops used for and how they work?
3> what is NF and END?

thank you guys

BR,
Ewa

---------- Post updated at 01:32 PM ---------- Previous update was at 07:23 AM ----------

Hello Guys !

i'm new to shell so please if anyone could explain the following things in detail

1> F"[,.?\! ]" why we used it? and what all these sign (,.?\!) means here can we add more?
2> what are the two for loops used for and how they work?
3> what is NF and END?

thank you guys

BR,
Ewa

Please don't bump.

-F tells awk what to use as a separator -- where fields stop and start. It's a regular expression. Any single , . ? \ ! will stop the current record and start the next.

The first for-loop:

Code:

for (i=1;i<=NF;i++) {arr[$i]++}

loops through i=1, i=2, i=3, ..., i=NF, incrementing arr[$i] each time.

Note the red $, it's important: if i is 1, $i becomes field 1.

So if you had fields A B C D E, it'd do arr["A"]++, then arr["B"]++, then arr["C"]++, and so forth.

NF is a special awk variable for "number of fields". Fields go from 1 to NF inclusive. You can use $NF to mean "the contents of the last field".

Another useful special variable is NR, the 'number of records'. Usually this'd be the line number, but awk can be used to operate on larger blocks than lines, so they consider each thing a 'record' instead.

Already explained NF.

I'll explain about awk codeblocks in general.

The usual {} global code block gets run once for every line, with updated values of NF, NR, $1,$2,... and so forth each time.

You're allowed to have more than one of them.

Code:

echo asdf | awk '{ print }
{ print }'

will print 'asdf' twice.

You can put statements before the block which control when they are run, and statements after the blocks which control when they print. The entire line is printed when you print that way. 'echo asdf | awk '{} 1' will print 'asdf' since the expression '1' is considered always true. You could put 'NR=5' in it instead so it'd only print the fifth line.

END {} tells a code block to run once, after all input has been processed. Useful for printing out things that've been stored but not printed earlier.

BEGIN {} tells a code block to run before any input has been processed. Useful for setting up variables.

/regex/ {} tells a code block to only run when the current line matches the given regular expression.


You can mix and match them however you like, i.e.

Code:

# Only run the code block if NR is 1.
# Only print the line if it matches /sd/.
echo asdf | awk 'NR==1 {} /sd/'

Hi Corona !

thanks dear you explained it in a very detailed level, help appreciated... i'm working with a similar problem from two days if i couldn't solve, i'll need help of you guys can i post it here because it is very simple in nature

---------- Post updated at 08:44 AM ---------- Previous update was at 03:56 AM ----------

Hi Guys !

i couldn't made it so here is my question

i am only interested in the first column of each line and it should check how many times string or numerical value is repeated in the first column in the whole file

for example

he is a good boy
he goes to school
2 is less then 3
he is very hard working
she is from NY
she lives with her parents
they all are playing
he is from NJ
2 and 2 makes four
2 is greater than 1

produce an output in asceding order regarding with such format as given below

Subject - Repeated
he - 4
2 - 3
she - 2
they - 1


is it possible using nawk or awk?


Thanks in advance

BR

Ewa

That's just a simplified version of what you already did...

Code:

awk '{ C[$1]++; }
END { for(K in C) print K, C[K]; }'

Hi Corona !

Thanks... your help is appreciated your solution worked

cheers!

BR

Ewa

hi,
I know you've already got a solution but just to say there is another way which gives you pretty much the same output you wanted:

Code:

grep -o '^\<[[:alnum:]]*\>' yourtextfile  | sort | uniq -c | sort -nr

* grep -o '^\<[[:alnum:]]*\>' finds the first alphanumeric word (using \< and \>, see the grep manpage for an explanation) on the line. If you remove the "^" it will give you word frequency for every word in the file.
* the option -o means only print the matched pattern, which is often extremely useful
So you've already now extracted all the first words from your file, you just have to count the frequency of them, which you can do with uniq -c after they're ordered so duplicates are adjacent. The final sort -r (reverse order) puts them in the ordered you wanted.