How to do string separation using using keyword? - bash

Question

I have the STRING as given below. There is no specific separator between each key. The only way is to identify the keys is using the keyword "key_1" or "key_2" etc..
All keys begin with "key_" and can never appear in the value of another:
STRING="key_1=mislanious_string1 key_2=miscellaneous_string2"
I want the output as below.
echo $STRING1 should print:
key_1=mislanious_string1
echo $STRING2 should print:
key_2=mislanious_string2
e.g:
If STRING="key_1=foobarzkey_2=bash" , then the output should look like , STRING1=key_1=foobarz and STRING2=key_2=bash.
There may be more keys like key_1 , key_2 , key_3 etc. Each key starts with "key_" and can never appear in the value of another:
How to this in UNIX bash shell?

Answer 1

Using grep -P (PCRE) to support multiple key-value pairs in input:
STRING="key_1=mislanious_string1key_2=miscellaneous_string2key_3=fookey_4=BASH"
grep -oP 'key_[^=]+=.*?(?=key_|$)' <<< "$STRING"
key_1=mislanious_string1
key_2=miscellaneous_string2
key_3=foo
key_4=BASH
To store them into BASH array you can use:
read -d '' -ra arr < <(grep -oP 'key_[^=]+=.*?(?=key_|$)' <<< "$STRING")
printf "%s\n" "${arr[#]}"
key_1=mislanious_string1
key_2=miscellaneous_string2
key_3=foo
key_4=BASH
declare -p arr
declare -a arr='([0]="key_1=mislanious_string1" [1]="key_2=miscellaneous_string2" [2]="key_3=foo" [3]="key_4=BASH")'
UPDATE:: Here is a pure BASH (non-gnu) way of splitting these strings. We first insert an invisible character before every occurrence of key_ string and then use that for splitting the string:
STRING="key_1=mislanious_string1key_2=miscellaneous_string2key_3=fookey_4=BASH"
c=$'\x06'
s="${STRING//key_/${c}key_}"
arr=()
while [[ "$s" =~ ${c}(key_[^=]+=[^${c}]+)(.*) ]]; do
arr+=( "${BASH_REMATCH[1]}" )
s="${BASH_REMATCH[2]}"
done
Then to test:
printf "<%s>\n" "${arr[#]}"
<key_1=mislanious_string1>
<key_2=miscellaneous_string2>
<key_3=foo>
<key_4=BASH>

Answer 2

I like anubhava's grep -oP solution best. Here's an awk solution:
STRING="key_15=foobarzkey_3=bash"
awk -v RS="key_" 'NR>1{split($0, a, /=/); print "STRING" a[1] "=" RS $0}' <<< "$STRING"
STRING15=key_15=foobarz
STRING3=key_3=bash
So, to create that output as shell variables
eval $(awk -v RS="key_" 'NR>1{split($0, a, /=/); print "STRING" a[1] "=" RS $0}' <<< "$STRING")
echo $STRING3 # => key_3=bash
echo $STRING15 # => key_15=foobarz

Answer 3

This answer originally didn't recognize keys not preceded by whitespace. This has been fixed. In its current form this answer provides value as a portable solution. If you disagree, please let me know.
The answers provided by Glenn Jackman and anubhava are helpful, but use GNU extensions not available on all platforms (grep -P, awk with a multi-char. RS value).
Here's a POSIX-compliant sed solution that should work on most platforms, using either bash, ksh, or zsh as the shell:
str='key_1=mislanious_string1 key_2=miscellaneous_string2key_3=last'
while read -r varDef; do
[[ -n $varDef ]] && typeset "$varDef"
done < <(sed 's/\(key_\([0-9]\{1,\}\)=\)/\'$'\n''string\2=\1/g' <<<"$str")
#'# Print the variables created ($string1, $string2, $string3).
typeset -p ${!string#}
Note that lowercase variable names (string1, ...) are used so as to prevent potential conflicts with environment variables.
sed is used to split the string into key-value tokens each on their own line, preceded by the desired target variable name and =, effectively outputting shell variable assignments; e.g., for key_1, the sed command passes out:
string1=key_1=mislanious_string1 
The while loop then reads each output line and uses typeset to declare and assign the variable (note that typeset was chosen for ksh compatibility - while typeset also works in bash and zsh you'd typically use declare there); [[ -n $varDef ]] ignores the empty line that the sed output starts with.
Note: This solution trims trailing whitespace from values, consistent with the example in the question. This trimming happens due to use of read with the default $IFS value (internal field separators) - to preserve trailing whitespace, simply use IFS= read instead of just read.
Also note that use of process substitution to provide input (while ... <(sed ...)) (as opposed to a pipeline (sed ... | while ...) is required to ensure that the variables are defined in the current shell (rather than in a subshell, which would result in variables not visible to the current shell).
Some background info on what makes the above sed command POSIX-compliant:
POSIX only mandates basic regular expressions for sed, which takes away many features (e.g., quantifiers ? and +, alternation (|)) and makes escaping more cumbersome (e.g., ( and ) must be \-escaped).
POSIX sed also doesn't support escape sequences such as \n in replacement strings passed to s, so ANSI-C quoting is used to splice an \-escaped actual newline into the replacement string using $'\n'.
As an example of how useful the non-POSIX GNU sed extensions are, here's an equivalent command taking full advantage of GNU sed's features (extended regular expressions, support for \n), resulting in a shorter and more readable command:
sed -r 's/(key_([0-9]+)=)/\nstring\2=\1/g' <<<"$str"

Answer 4

Sometimes the simplest solution can be overlooked:
STRING="key_1=mislanious_string1key_2=miscellaneous_string2"
read STRING1 STRING2<<<${STRING//key_/ key_}
echo $STRING1
echo $STRING2