Extract String before bracket and create new line - bash

Question

I have data in below format
ABC-ERW 12344 ZYX 12345
FFANKN 2345 QW [123457, 89053]
FAFDJ-ER 1234 MNO [6532, 789, 234578]
I want to create the data in below format using sed or awk.
ABC-ERW 12344 ZYX 12345
FFANKN 2345 QW 123457
FFANKN 2345 QW 89053
FAFDJ-ER 1234 MNO 6532
FAFDJ-ER 1234 MNO 789
FAFDJ-ER 1234 MNO 234578
I can extract the data before bracket but I don't know how to concatenate the same with data from bracket repeatedly.
My Effort :--
# !/bin/bash
while IFS= read -r line
do
echo "$line"
cnt=`echo $line | grep -o "\[" | wc -l`
if [ $cnt -gt 0 ]
then
startstr=`echo $line | awk -F[ '{print $1}'`
echo $startstr
intrstr=`echo $line | cut -d "[" -f2 | cut -d "]" -f1`
echo $intrstr
else
echo "$line" >> newfile.txt
fi
done < 1.txt
I am able to get the first part and also keep the rows not having "[" in new file but I dont know how to get the values in "[" and pass it at end as number of variables in "[" keep changing randomly.
Regards

Answer 1

With your shown samples, please try following awkcode.
awk '
match($0,/\[[^]]*\]$/){
num=split(substr($0,RSTART+1,RLENGTH-2),arr,", ")
for(i=1;i<=num;i++){
print substr($0,1,RSTART-1) arr[i]
}
next
}
1
' Input_file
Explanation: Adding detailed explanation for above code.
awk ' ##Starting awk program from here.
match($0,/\[[^]]*\]$/){ ##Using match function to match from [ till ] at the end of line.
num=split(substr($0,RSTART+1,RLENGTH-2),arr,", ") ##Splitting matched values by regex above and passing into array named arr with delimiters comma and space.
for(i=1;i<=num;i++){ ##Running for loop till value of num.
print substr($0,1,RSTART-1) arr[i] ##printing sub string before matched along with element of arr with index of i.
}
next ##next will skip all further statements from here.
}
1 ##1 will print current line.
' Input_file ##Mentioning Input_file name here.

Answer 2

Suggesting simple awk script:
awk 'NR==1{print}{for (i=2;i<NF;i++)print $1, $i}' FS="( \\\[)|(, )|(\\\]$)" input.1.txt
Explanation:
FS="( \\\[)|(, )|(\\\]$)" Set awk field seperator to be either [ , ]EOL
This will make the interesting fields $2 ---> $FN to be appended to $1
NR==1{print} print first line only as it is.
{for (i=2;i<NF;i++)print $1, $i} for 2nd line on, print: field $1 appended by current field.

Answer 3

This might work for you (GNU sed):
sed -E '/(.*)\[([^,]*), /{s//\1\2\n\1[/;P;D};s/[][]//g' file
Match the string up to the opening square bracket and also the string after before the comma and space.
Replace the entire match by the leading and trailing matching strings, followed be a newline and the leading matching string.
Print/delete the first line and repeat.
The last line of any repeat above will fail because there is not trailing comma space, in which case the opening and closing square brackets should also be removed.
Alternative:
sed -E ':a;s/([^\n]*)\[([^,]*), /\1\2\n\1[/;ta;s/[][]//g' file