Extract value for a key in a key/pair string - bash

Question

I have key value pairs in a string like this:
key1 = "value1"
key2 = "value2"
key3 = "value3"
In a bash script, I need to extract the value of one of the keys like for key2, I should get value2, not in quote.
My bash script needs to work in both Redhat and Ubuntu Linux hosts.
What would be the easiest and most reliable way of doing this?
I tried something like this simplified script:
pattern='key2\s*=\s*\"(.*?)\".*$'
if [[ "$content" =~ $pattern ]]
then
key2="${BASH_REMATCH[1]}"
echo "key2: $key2"
else
echo 'not found'
fi
But it does not work consistently.
Any better/easier/more reliable way of doing this?

Answer 1

To separate the key and value from your $content variable, you can use:
[[ $content =~ (^[^ ]+)[[:blank:]]*=[[:blank:]]*[[:punct:]](.*)[[:punct:]]$ ]]
That will properly populate the BASH_REMATCH array with both values where your key is in BASH_REMATCH[1] and the value in BASH_REMATCH[2].
Explanation
In bash the [[...]] treats what appears on the right side of =~ as an extended regular expression and matched according to man 3 regex. See man 1 bash under the section heading for [[ expression ]] (4th paragraph). Sub-expressions in parenthesis (..) are saved in the array variable BASH_REMATCH with BASH_REMATCH[0] containing the entire portion of the string (your $content) and each remaining elements containing the sub-expressions enclosed in (..) in the order the parenthesis appear in the regex.
The Regular Expression (^[^ ]+)[[:blank:]]*=[[:blank:]]*[[:punct:]](.*)[[:punct:]]$ is explained as:
(^[^ ]+) - '^' anchored at the beginning of the line, [^ ]+ match one or more characters that are not a space. Since this sub-expression is enclosed in (..) it will be saved as BASH_REMATCH[1], followed by;
[[:blank:]]* - zero or more whitespace characters, followed by;
= - an equal sign, followed by;
[[:blank:]]* - zero or more whitespace characters, followed by;
[[:punct:]] - a punctuation character (matching the '"', which avoids caveats associated with using quotes within the regex), followed by the sub-expression;
(.*) - zero or more characters (the rest of the characters), and since it is a sub-expression in (..) it the characters will be stored in BASH_REMATCH[2], followed by;
[[:punct:]] - a punctuation character (matching the '"' ... ditto), at the;
$ - end of line anchor.
So if you match what your key and value input lines separated by an = sign, it will separate the key and value into the array BASH_REMATCH as you wanted.

Answer 2

Bash supports BRE only and you cannot use \s and .*?.
As an alternative, please try:
while IFS= read -r content; do
# pattern='key2\s*=\s*\"(.*)\".*$'
pattern='key2[[:blank:]]*=[[:blank:]]*"([^"]*)"'
if [[ $content =~ $pattern ]]
then
key2="${BASH_REMATCH[1]}"
echo "key2: $key2"
(( found++ ))
fi
done < input-file.txt
if (( found == 0 )); then
echo "not found"
fi

Answer 3

What you start talking about key-value pairs, it is best to use an associative array:
declare -A map
Now looking at your lines, they look like key = "value" where we assume that:
value is always encapsulated by double quotes, but also could contain a quote
an unknown number of white spaces is before and/or after the equal sign.
So assuming we have a variable line which contains key = "value", the following operations will extract that value:
key="${line%%=*}"; key="${key// /}"
value="${line#*=}"; value="${value#*\042}"; value="${value%\042*}"
IFS=" \t=" read -r value _ <<<"$line"
This allows us now to have something like:
declare -A map
while read -r line; do
key="${line%%=*}"; key="${key// /}"
value="${line#*=}"; value="${value#*\042}"; value="${value%\042*}"
map["$key"]="$value"
done <inputfile

Answer 4

With awk:
awk -v key="key2" '$1 == key { gsub("\"","",$3);print $3 }' <<< "$string"
Reading the output of the variable called string, pass the required key in as a variable called key and then if the first space delimited field is equal to the key, remove the quotes from the third field with the gsub function and print.

Answer 5

Ok, after spending so many hours, this is how I solved the problem:
If you don't know where your script will run and what type of file (win/mac/linux) are you reading:
Try to avoid non-greedy macth in linux bash instead of tweaking diffrent switches.
don't trus end of line match $ when you might get data from windows or mac
This post solved my problem: Non greedy text matching and extrapolating in bash
This pattern works for me in may linux environments and all type of end of lines:
pattern='key2\s*=\s*"([^"]*)"'
The value is in BASH_REMATCH[1]