UNIX for Dummies Questions & Answers

I am really lost I don't know what this line does. Please help I'm very lost. Thanks in advance.

cat CPROGRAMS.c
|sed 's/[^a-z(_]/ /g'|tr ' ' '\012'
|grep '[a-z]'
|sed 's/^[(]*/ /'
|grep '($'|sort -u|tr -d "("`

If you really want to know, run each part one-by-one and see how it changes the output...

For example, run:
cat CPROGRAMS.c | sed 's/[^a-z(_]/ /g'
(replaces with blanks anything that is not a parenthesis, underscore, or small letter)

then run:
cat CPROGRAMS.c | sed 's/[^a-z(_]/ /g' | tr ' ' '\012'
(takes it a step further by turning those blank spaces into return lines)

and so on... at first glance, there's probably a much shorter way to do what you're trying to do. What are you trying to do btw?

I read a bunch of C programs and put them in a file.

Now I want to extract all the funtions that start with _

I'm a little confused with the concept of SED and GREP and how to use Regular Expressions and Search Patterns with theses commands.

Thanks once again...

oreilly has a great book on regular expressions.
REGEX's are an essential to anyone scripting or programming.

as far as the pipe. just as was said in various other posts asking about the pipe. it takes the output from one command and feeds it into another command.

also if you are confused about what the line does the first place to start is by reading the man pages for each command used.

this should clear it up enuff so you can fill in the gaps and get a grasp on it.

Oh well, I think you really should read more books, but I was bored and stepped through that line piece by piece, so...

1) sed 's/[^a-z(_]/ /g'

Replace anything that's not a small letter, left parenthesis or underscore with a blank space

2) tr ' ' '\012'

Replaces every blank space with a return character

3) grep '[a-z]'

Only display the lines containing a small letter in them

4) sed 's/^[(]*/ /'

Inserts a blank space at the beginning of every line, erasing the left parenthesis from the beginning of any lines that might have one

5) grep '($'

Display only lines that end with a left parenthesis

6) sort -u

Sort the result of the last command and if one entry is displayed multiple times

7) tr -d "("

Remove the left parenthesis from the end of the lines that were just sorted

------------------------

If all you're trying to do is display the name of the functions, then you can do something like:

grep '^_.*(.*)' CPROGRAMS.c | awk -F"(" '{print $1}' | sort -u

There's probably an even shorter way, but this is an improvement.