bash: store/update text data [closed] - arrays

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so for reading the list of file, I use this code here below:
IFS=$'\n' read -d '' -r -a data < ./somefolder/mytext.txt
for i in {0..9} #i know that i have 10 items, thats why i use 0..9
do
echo "${data[$i]}"
done
lets say i have 1-10 in the txt file, so it should print like below:
1
2
3
4
5
6
7
8
9
10
Questions:
is there any simpler way to read/write the text list than this?
how to save/update/overwrite data of mytext.txt? lets say change 4 to 88 for example.
Full example:
#!bin/bash
IFS=$'\n' read -d '' -r -a data < ./somefolder/mytext.txt
for i in {0..9} #i know that i have 10 items, thats why i use 0..9
do
echo "${data[$i]}"
done
echo "change 4 to anything"
read any
update(){
for n in {0..9}
do
if [[ n == 3 ]]; then
echo any
else
echo "${data[$n]}"
fi
done
}
update > ./somefolder/mytext.txt
#i dont know what i should do, it throws some errors saying syntax error
echo "saved"
exit 0

Answer 1

This is the code and output of the code, it is not the same as you describe in the comments.
printf '%s\n' {a..z} > file.txt
cat file.txt
a
b
c
d
e
f
g
h
i
j
k
l
m
n
o
p
q
r
s
t
u
v
w
x
y
z
A quick way of showing line numbers by using grep
grep -n . file.txt
A function to loop through an array.
func() {
n=1
for f; do
if (( n == 3 )); then
printf '%d %s\n' "$n" foo
else
printf '%d %s\n' "$n" "$f"
fi
((n++))
done
}
mapfile -t array < file.txt
func "${array[#]}"
Output
1 a
2 b
3 foo
4 d
5 e
6 f
7 g
8 h
9 i
10 j
11 k
12 l
13 m
14 n
15 o
16 p
17 q
18 r
19 s
20 t
21 u
22 v
23 w
24 x
25 y
26 z
On the other hand if you just want to replace everything with anything at a certain line and and ed is acceptable/available.
#!/usr/bin/env bash
printf '%s\n' ,n | ed -s file.txt
read -rp 'Change 4 to anything: ' input
printf '%s\n' "4c" "$input" . ,n w | ed -s file.txt
A more flexible version of the previous script.
#!/usr/bin/env bash
total=$(printf '%s\n' '$=' | ed -s file.txt)
printf '%s\n' ,n | ed -s file.txt
read -rp 'Enter the line number you want to change: ' int
if [[ $int == *[!0-9]* ]]; then
printf >&2 '%s is not an int\n' "$int"
exit 1
elif (( int > total )); then
printf >&2 '%s is out of range!' "$int"
exit 1
fi
read -rp "Enter the replacement at line $int: " input
printf '%s\n' "${int}c" "$input" . ,n w | ed -s file.txt
Caveat The file.txt name and path is still hard coded to the script, just add an additional read for the the file.