Get string from variable lists in Bash

Trying your code

I tried your command and get this as output :

$kw_var1
$kw_var2

$kw_var3



$kw_var4


$kw_var5

You had the wrong output because you chose the first field when you used cut instead of the second.

Fixing cut command

for param in $(cat test.txt | grep "kw\_"); do echo $(echo '$'$param | cut -s -d '=' -f2); done

Returns :

'string1'
'string
'this


'does

'maybe'

Fixing IFS

You used a for in loop but it does not iterate over newlines, it iterates over spaces. You need to change the IFS (Internal Field Separator) variable first :

IFS=$'\n'; for param in $(cat <file> | grep "kw\_"); do echo $(echo $param | cut -s -d '=' -f2); done

Output :

'string1'
'string 2'
'this is string 3'
'does not matter'
'maybe'

Using printf

To get the output on one line, you can use printf instead of echo :

for param in $(cat <file> | grep "kw\_"); do printf "$(echo $param | cut -s -d '=' -f2) "; done; printf "\n"

Output :

'string1' 'string 2' 'this is string 3' 'does not matter' 'maybe' 

Using while

You could simplify the command and use a while read statement that iterates directly over lines :

cat <file> | grep "kw\_" | cut -d"=" -f2 | while read line; do printf "${line} "; done; printf "\n"

Using awk

Last but not least, you can use awk which radically simplifies your code:

awk -F"=" '/kw_/{printf "%s ", $2}END{print ""}' <file>

Output :

'string1' 'string 2' 'this is string 3' 'does not matter' 'maybe'

If the extra space at the end of the line is annoying, you can do this :

awk -F"=" '/kw_/{printf "%s%s", delim, $2; delim=" "}END{print ""}' <file>

Awk explained :

# Using = as delimiter
awk -F"=" '
    # If line contains kw_
    /kw_/{
        # Prints second field
        printf "%s%s", delim, $2;
        delim=" "
    }
    END{
        # Prints newline
        print ""
    }' <file>

Final code

list_of_values=$(awk -F"=" '/kw_/{printf "%s%s", delim, $2; delim=" "}END{print ""}' $file.env)

Make two arrays of your bunch of variables, then you can easily iterate over them like this

#!/bin/bash

kw=(
'string1'
'string 2'
'this is string 3'
'does not matter'
'maybe'
)

w=(
'qwert_1'
'qwert_2'
'qwert_3'
'qwert_4'
)

for i in {1..5}
do
    echo -n "\"${kw[$i]}\" "
done

echo

for i in {1..4}
do
    echo -n "\"${w[$i]}\" "
done

echo

I used dynamic references.

$: out="$( . file.env; for r in ${!kw_*}; do printf "'%s' " "${!r}"; done; echo )"
$: echo "$out"

'string1' 'string 2' 'this is string 3' 'does not matter' 'maybe'

Your attempt uses a few practices that aren't recommended, and contains a few syntax errors:

• You use $file.env, but it should be just file.env
• Don't use for to read lines from a file (see this article)
• echo $(cmd) is the same as just cmd plus globbing and word splitting, which often isn't what you want
• echo -e '$'$param is going to print a literal $ sign
• cut -f1 is selecting the first field, but you want the second one

This is a solution "in the spirit" of what you tried, but using just Bash:

list=$(
    while IFS='=' read -r key val; do
        [[ $key == kw_* ]] && printf '%s ' "$val"
    done < file.env
)
list=${list% }   # Remove trailing blank

If you deal with strings containing spaces, though, it's generally advisable to use an array instead. Since file.env is valid Bash, we can source the lines we're interested in and then build an array with the values of all the kw_ variables:

source <(grep '^kw_' file.env)
declare -n var
for var in "${!kw_@}"; do list+=("$var"); done

The array now contains one string per element, without the literal single quotes:

$ printf '%s\n' "${list[@]}"
string1
string 2
this is string 3
does not matter
maybe

declare -n sets var to a nameref: it is treated as if it actually were the variable whose name it holds. This requires Bash 4.3 or newer.