Using awk in a wrong approach - bash

Question

I am told I used awk in a wrong approach in the below code, but I am dumbfounded as to how to improve my code so that it is more simpler to read.
read -r bookName
read -r authorName
if grep -iqx "$bookName:$authorName" cutText.txt
then
lineNum=`awk -v bookName="$bookName" -v authorName="$authorName" '$0 ~ bookName ":" authorName {print NR} BEGIN{IGNORECASE=1}' BookDB.txt`
echo "Enter a new title"
read -r newTitle
awk -F":" -v bookName="$bookName" -v newTitle="$newTitle" -v lineNum="$lineNum" 'NR==lineNum{gsub(bookName, newTitle)}1' cutText.txt > temp2.txt
mv -f temp2.txt cutText.txt
else
echo "Error"
fi
My cutText.txt contains content as shown below:
Hairy Potter:Rihanna
MARY IS A LITTLE LAMB:Kenny
Sing along:May
This program basically update a new title in cutText.txt. If a user wants to change MARY IS A LITTLE LAMB to Mary is not a lamb, he will enter the new title and cutText.txt will replace the original title with Mary is not a lamb.
A problem arises now that if a user enter "Mary is a little lamb" for $newTitle, this code of works just doesn't work, because it does take the case into account.
It will only work is user types "MARY IS A LITTLE LAMB". I came to be aware that BEGIN{IGNORECASE=1} is gawk-sepcific, therefore it cannot be used in awk.
How can I script this better so I can ignore case in user input? Thank you!

Answer 1

This uses exact string matching and so cannot fail on partial matches or if your old title contains : or regexp metacharacters or if the new title contains backreferences (e.g. &) or if a backslash (\) appears in any field or any of the other situations that your other scripts to date will fail on:
$ cat tst.sh
read -r oldTitle
read -r authorName
echo "Enter a new title"
read -r newTitle
awk '
BEGIN {
ot=ARGV[1]; nt=ARGV[2]; an=ARGV[3]
ARGV[1] = ARGV[2] = ARGV[3] = ""
}
tolower($0) == tolower(ot":"an) {
$0 = nt":"an
found = 1
}
{ print }
END {
if ( !found ) {
print "Error" | "cat>&2"
}
}
' "$oldTitle" "$newTitle" "$authorName" cutText.txt > temp2.txt &&
mv -f temp2.txt cutText.txt
.
$ cat cutText.txt
Hairy Potter:Rihanna
MARY IS A LITTLE LAMB:Kenny
Sing along:May
$ ./tst.sh
mary is a little lamb
kenny
Enter a new title
Mary is not a lamb
$ cat cutText.txt
Hairy Potter:Rihanna
Mary is not a lamb:kenny
Sing along:May
I'm populating the awk variables from ARGV[] because if I populated them using -v var=val or var=val in the arg list then any backslashes would be interpreted and so \t, for example, would become a literal tab character. See the shell FAQ article I wrote about that a long time ago - http://cfajohnson.com/shell/cus-faq-2.html#Q24.
I changed bookName to oldTitle, btw just because that seems to make more sense in relation to newTitle. No functional difference.
When doing any text manipulation it's extremely important to understand the differences between strings and the various regexp flavors (BREs/EREs/PCREs) and between partial and full matches.
grep operates on BREs by default, on EREs given the -E arg, on PCREs given the -P arg, and on strings given the -F arg.
sed operates on BREs by default, on EREs given the -E arg. sed does not support PCREs. sed also cannot operate on strings and to make your regexps behave as if they were strings is painful, see is-it-possible-to-escape-regex-metacharacters-reliably-with-sed.
awk operates on both EREs and strings by default. You just use EREs with regexp operators and strings with string operators (see https://www.gnu.org/software/gawk/manual/gawk.html#String-Functions).
So if, as in your case, you need all characters in your text treated literally then that is a string, not a regexp, so you should not be using sed on it, and if you want to quickly find a string in a file and are happy with a partial match, you should use grep, but if you want to do anything beyond that such as change a string in a file or do an exact match then you should use awk.

Answer 2

To get you started. Create files
r.awk
function asplit(str, arr, sep, temp, i, n) { # make an assoc array from str
n = split(str, temp, sep)
for (i = 1; i <= n; i++)
arr[temp[i]]++
return n
}
function regexpify(s, back, quote, rest, all, meta, n, c, u, l, ans) {
back = "\\"; quote = "\"";
rest = "^$.[]|()*+?"
all = back quote rest
asplit(all, meta, "")
n = length(s)
for (i=1; i<=n; i++) {
c = substr(s, i, 1)
if (c in meta)
ans = ans back c
else if ((u = toupper(c)) != (l = tolower(c)))
ans = ans "[" l u "]"
else
ans = ans c
}
return ans
}
BEGIN {
old = regexpify(old)
sep = ":"; m = length(sep)
}
NR == n {
i = index($0, sep)
fst = substr($0, 1, i-m)
scn = substr($0, i+m )
gsub(old, new, fst)
print fst sep scn
next
}
{
print
}
cutText.txt
Hairy Potter:Rihanna
MARY IS A LITTLE LAMB:Kenny
Sing along:May
Usage:
awk -v n=2 -v old="MArY iS A LIttLE lAmb" -v new="Mary is not a lamb" -f r.awk cutText.txt
Expected output:
Hairy Potter:Rihanna
Mary is not a lamb:Kenny
Sing along:May

Answer 3

OK GUYS I JUST REALISED I AM DUMB AS ****
I was tearing my hair out for the whole day and all I had to do was to do this.
lineNum=`grep -in "$bookName:$authorName" BookDB.txt | cut -f1 -d":"`
sed -i "${lineNum}s/$bookName/$newTitle/I" BookDB.txt cutText.txt
Omg I feel like killing myself.