Unix bash cutting and grep - bash

Question

I have a text file called db.txt.
Some sample lines from the file goes as such:
Harry Potter and the Sorcerer's Stone:J.K. Rowling:21.95:100:200
Harry Potter and the Chamber of Secrets:J.K. Rowling:21.95:150:300
Lord of the Rings, The Fellowship of the Ring:J.R.R. Tolkien:32.00:500:500
A Game of Thrones:George R.R. Martin:44.50:300:250
Then in my script, I have the following lines:
echo "Enter title:"
read TITLE
cut -d ":" -f 1 db.txt | grep -iw "$TITLE" | while read LINE
do
STRING="`echo $LINE | cut -d ":" -f 1`,"
STRING="$STRING `echo $LINE | cut -d ":" -f 2`, "
STRING=" \$$STRING`echo $LINE | cut -d ":" -f 3`,"
STRING=" $STRING`echo $LINE | cut -d ":" -f 4`,"
STRING=" $STRING`echo $LINE | cut -d ":" -f 5`"
done
Is there a way to grep a specific field from cut and then pass in the full line into the while loop?
For example, if I entered "Harry Potter",
it should display:
Harry Potter and the Sorcerer's Stone, J.K. Rowling, $21.95, 100, 200
Harry Potter and the Chamber of Secrets, J.K. Rowling, $21.95, 150, 300

Answer 1

You can do this without cut, and without grep if you're ok with bash's regular expression matching (or can use shell pattern matching instead).
The idea would be to read the file line by line, then split the line into an array.
Once you've got that, do the comparisons and output you want.
Here's a demo of the technique:
#! /bin/bash
echo "Title:"
read title
# shopt -s nocasematch # if you want case-insensitive matching
while read line ; do # this read takes data from input.txt, see
# end of loop
IFS=: read -a parts <<< "$line" # this splits the line on ":" into
# an array called parts
if [[ ${parts[0]} =~ $title ]] ; then # regex matching
printf "%s -- %s\n" "${parts[1]}" "${parts[2]}"
fi
done < input.txt

Answer 2

The next step up from grep and cut is awk. Unless you must do this using bash (is this homework?), then awk would make things considerably easier:
awk -F: '/harry potter/ { sub(/^/,"$",$(NF-2)); print }' IGNORECASE=1 OFS=", " db.txt
Test input:
Harry Potter and the Sorcerer's Stone:J.K. Rowling:21.95:100:200
Harry Potter and the Chamber of Secrets:J.K. Rowling:21.95:150:300
Lord of the Rings, The Fellowship of the Ring:J.R.R. Tolkien:32.00:500:500
A Game of Thrones:George R.R. Martin:44.50:300:250
Test output:
Harry Potter and the Sorcerer's Stone, J.K. Rowling, $21.95, 100, 200
Harry Potter and the Chamber of Secrets, J.K. Rowling, $21.95, 150, 300

Answer 3

read -p "Enter title: " TITLE
while IFS=: read title author price x y; do
if [[ ${title,,} == *${TITLE,,}* ]]; then
printf "%s, %s, $%s, %s, %s\n" "$title" "$author" "$price" "$x" "$y"
fi
done < db.txt
The test in the if command does a simple glob-match but case insensitively, so it will match if the user enters "potter".
Or, use sed to change the separators:
read -p "Enter title: " TITLE
sed '/'"$TITLE"'/I!d; s/:/, /g' db.txt
which means delete all lines that do not match the TITLE, then transform the separator.

Answer 4

The easiest method of doing this is to look over the grep results
#!/bin/bash
read -p "Enter title: " TITLE
FILENAME="db.txt"
IFS=$'\n'
for LINE in `grep -iw "Harry Potter" "$FILENAME"`; do
echo $LINE | awk 'BEGIN { FS = ":" } ; { print $1, $2, $3, $4, $5 }'
done
The IFS change changes the delimiter to a new line rather than a space and the FS in the awk command changes the delimiter to the : to allow access to the fields

Answer 5

I know you didn't specify it, but awk is probably the best tool to use for this task. It combines cut, sed, and grep into one convenient and easy to use tool. Well, convenient tool...
To understand awk, you have to understand a few things:
Awk is a programming language. It has built in logic and variables.
Awk assumes a read loop reading each and every line.
Awk programs must be surrounded by curly braces.
Not only curly braces, but Awk parsing variables start with dollar signs. Therefore, you need to put your Awk programs surrounded by single quotes to keep the shell out of it.
Awk automatically parses each line based upon the field separator. The default field separator is a while space, but you can change that via the -f parameter.
Each field gets a special variable. THe first field is $1, the next field is $2, etc. The entire line is $0.
Here's your Awk statement:
awk -F: '{
title = $1
author = $2
price = $3
pages_read_until_i_got_bored=$4
pages = $5
print "I read " pages_read_until_i_gob_bored "pages out of " $pages " pages of " $title " by " $author "."
}' $file
Of course, the whole thing could be a single line too:
awk -F: '{ print "I read " $4 " pages " out of " $5 " of " $1 " by " $2 "." }' $file
Just wanted to emphasize the programability of Awk and how it can be used to do this type of parsing.
If your question is how to enter this information and put it into environment variables, Glenn Jackman's answer is the best.

Answer 6

If you can use sed this would be a solution
read -p "Enter title: " TITLE
sed -n -e 's/^\([^:]\+:\)\{2\}/\0$/' -e 's/:/, /g' -e "/^$TITLE/Ip" db.txt
Short explanation what it does
-n tells sed not to print any lines
-e 's/^\([^:]\+:\)\{2\}/\0$/' matches for the 2nd : and adds a $ after it
-e 's/:/, /g' replaces all : with , and a following whitespace
-e "/^$TITLE/Ip" tells sed to print all lines which start with $TITLE (that's the p) and I tells sed to match case-insensitive