hello!

I'm learning "grep" and "sed" command; So I don't no exactly what the command line below, does :

command line: grep Shell /usr/share/doc/ | sed '/README\./d' | grep README | wc -l

thank you for answering

Your other thread about grep should tell you what grep does. Sed is a stream editor. Type in "man grep" and "man sed" for explanations as to what the commands do.

So read out the line: You're looking for the word Shell in /usr/share/doc, then sending it through sed, where it deletes all lines that contain an upper-case "README." Then it pipes it into grep for README, then to word count.

As it stands there, it makes no sense, since all the lines with README are getting deleted before they're counted.

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I'm no sed-spert but wonder if that is true; is it not only the lines with 'README.' that are deleted? The pipeline seems designed to count the number of occurrences of README that are not at the end of a sentence. Could turn out to be very popular, like sliced bread or hot cakes

Two sed links:
http://www.grymoire.com/Unix/Sed.html
http://sed.sourceforge.net/sedfaq.html

grep Shell /usr/share/doc/ | sed '/README\./d' | grep README | wc -l
The bold part searches for "Shell" in /usr/share/doc/. However, /usr/share/doc/ specifies a directory, not a file, therefore grep will not return any result. You should do grep Shell /usr/share/doc/some_file (assuming you're trying to search within a file).

grep Shell /usr/share/doc/ | sed '/README\./d' | grep README | wc -l
Pretending your first grep worked and returned "README.", the bold part, | sed '/README\./d', searches for "README." in the grep return and deletes it. For example:

$ echo -e "README.\nREADME\nREADME."
README.
README
README.
$ echo -e "README.\nREADME\nREADME." | sed '/README\./d'
README
$

grep Shell /usr/share/doc/ | sed '/README\./d' | grep README | wc -l
The bold part searches the result AFTER the first grep and sed commands for "README". Of which there is one in the result.

$ echo -e "README.\nREADME\nREADME."
README.
README
README.
$ echo -e "README.\nREADME\nREADME." | sed '/README\./d' | grep README
README
$

grep Shell /usr/share/doc/ | sed '/README\./d' | grep README | wc -l
The bold part then counts how many lines there are in after the first grep, sed, and second grep. The result would be one.

$ echo -e "README.\nREADME\nREADME." | sed '/README\./d' | grep README | wc -l
1
$

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the above can be done with just one awk command.

therefore, learn awk instead

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