Searching and deleting using Sed

gregarion · 01-07-2010, 02:13 PM

Hey guys ,im working on a mini project which basically use a simple database(Database.txt) which displays its information in this format :

apple
chiku
banana

Code:

#!/bin/bash
Title=
echo -n "Fruit to delete: "
read Fruit to delete

cat Database.txt | \
sed -e / $title /d > Database.txt

I tried typing out this coding bout for some reason , it gives me a error message saying

Code:

sed: -e expression #1, char 1: unterminated address regex

And instead of deleting the title i type in, for example , "apple", it deletes the whole text inside. How do i solve this problem?

Another problem which i am having is , when a database is displayed like this :
Fruit : Price : Quantity
apple : 20 : 30
banana : 30 : 40

how do i go about in making sure the whole row is deleted. For example, if i key in "apple" , to be deleted , all the information about apple should be gone. How do i do this?

slacker_et · 01-07-2010, 02:18 PM

"title" doesn't appeare to be defined.

--ET

jschiwal · 01-07-2010, 02:22 PM

Quote:

Originally Posted by gregarion

Hey guys ,im working on a mini project which basically use a simple database(Database.txt) which displays its information in this format :

apple
chiku
banana

Code:

#!/bin/bash
Title=
echo -n "Fruit to delete: "
read Fruit to delete

cat Database.txt | \
sed -e / $title /d > Database.txt

I tried typing out this coding bout for some reason , it gives me a error message saying

Code:

sed: -e expression #1, char 1: unterminated address regex

And instead of deleting the title i type in, for example , "apple", it deletes the whole text inside. How do i solve this problem?

Another problem which i am having is , when a database is displayed like this :
Fruit : Price : Quantity
apple : 20 : 30
banana : 30 : 40

how do i go about in making sure the whole row is deleted. For example, if i key in "apple" , to be deleted , all the information about apple should be gone. How do i do this?

You need to put the sed command in quotes.
sed '/'"$title"'/d' Databasefile.txt >NewDatabasefile.txt

Code:

Inserting extra spaces to make the sed part more readable:
sed ' / '  "$title"   ' /d '

You need to check your "read" command as well. It is still pseudocode.
For the highly structured text data you are using, it would be worthwhile
to learn about AWK as well. Your problem is better suited for awk.

* Don't use commands that read a file and write to the same file on same command line. The "> Database.txt" part is executed first, creating a new file and deleting the file you want to use for your input. This is a general rule and not just for sed. (note: You can use the -i option is sed for en-situ editing ).

* You don't need to cat the input file. The general form is
sed 'command(s)' inputfile >outputfile

Good Luck!

tuxdev · 01-07-2010, 02:28 PM

Code:

read title -p "Fruit to delete: "
sed -i -e "/$title/d" database

gregarion · 01-07-2010, 11:15 PM

Hey. Jshiwal, thanks for the help. I need to clarify with you. If I were to use awk, how would the coding be like? I read up on it but I can't seem to get it. How would It be able to retrieve the information I want. For example , if I were to search for apple, how will it pull out the information such as price and quantity.

jschiwal · 01-08-2010, 03:23 PM

This prints third record if the line contains "apple" and prints the second field.

Code:

echo 'apple : 20 : 30' | awk -F: '/apple/{print $3}'

This checks the first field for the apple pattern and prints the second and third field:

Code:

echo 'apple : 20 : 30' | awk -F: '$0 ~ /apple/{print $2,$3}'

Each field is assigned to a variable. $0 is the entire line. $1 is the first field, $2 the second and $3 is the third.
Since the "$" is used, enclose awk commands in single quotes so the shell doesn't expand them first as positional characters.
If you need a bash variable, the do the same thing as I showed you in my first post in this thread: awk -F: "/$fruit/"'{print $3}'
Use single quotes around awk variables and double around bash variables.

The info manual "GAWK: Effective Awk Programming" is very good. there are tutorials on the web as well.

gregarion · 01-09-2010, 11:24 AM

thank for the tip. do you happen to know any websites or links which have good tutorials and examples of different commands? those which i found normally just have tutorials on the basic commands and not much examples of how it can be used.

jschiwal · 01-10-2010, 02:42 AM

I bought the O'Reilly "Sed & Awk" book. The 2nd edition is in the stores. They may have the first edition available on the web.

Here is the "GAWK: Effective Awk Programming" book. http://books.google.com/books?id=D_u...age&q=&f=false

If you install the gawk package source code and run "./configure" and "make pdf" you can generate this book yourself.

drstupid · 01-10-2010, 03:53 AM

Good awk tips:

http://adminlinux.blogspot.com/2009/...rocessing.html

pixellany · 01-10-2010, 07:51 AM

http://www.grymoire.com/Unix/

Some of the best tutorials I have seen