Bash regexp to find part of string

This should help you

grep setSuperValue myfile.txt | grep -o "'. *'"  | tr -d "'" 

The grep -o will return all text that start with a single ' and ends with another ', including both quotes. Then use tr to get rid of the quotes.

You could also use cut:

 grep setSuperValue myfile.txt | cut -d"'" -f2

Or awk:

 grep setSuperValue myfile.txt | awk -F "'" '{print $2}'

This will split the line where the single quotes are and return the second value, that is what you are looking for.

Generally, to locate a string in multiple lines of data, external utilities will be much faster than looping over lines in Bash.

In your specific case, a single sed command will do what you want:

sed -n -r "s/^.*setSuperValue\('([^']+)'\).*$/\1/p" file

• Extended (-r) regular expression ^.*setSuperValue\('([^']+)'\).*$ matches any line containing setSuperValue('...') as a whole, captures whatever ... is in capture group \1, replaces the input line with that, and prints p the result.
  • Due to option -n, nothing else is printed.
  • Move the opening and closing ' inside (...) to include them in the captured value.

Note: If the input file contains multiple setSuperValue('...') lines, the command will print every match; either way, the command will process all lines.
To only print the 1st match and stop processing immediately after, modify the command as follows:

sed -n -r "/^.*setSuperValue\('([^']+)'\).*$/ {s//\1/;p;q}" file

• /.../ only matches lines containing setSuperValue('...'), causing the following {...} to be executed only for matching lines.
  • s// - i.e., not specifying a regex - implicitly performs substitution based on the same regex that matched the line at hand; p prints the result, and q quits processing altogether, meaning that processing stops once the fist match was found.

If you have already located a line of interest through other methods and are looking for a pure Bash method of extracting a substring based on a regex, use =~, Bash's regex-matching operator, which supports extended regular expressions and capture groups through the special ${BASH_REMATCH[@]} array variable:

$ sampleLine="... setSuperValue('sdfsdfd') ..."
$ [[ $sampleLine =~ "setSuperValue('"([^\']+)"')" ]] && echo "${BASH_REMATCH[1]}"
sdfsdfd

Note the careful quoting of the parts of the regex that should be taken literally, and how ${BASH_REMATCH[1]} refers to the first (and only) captured group.

You can parse the value from the line, using parameter expansion/substring removal without relying on any external tools:

#!/bin/bash

while read -r line; do
    value=$(expr "$line" : ".*setSuperValue('\(.*\)')")
    if [ "x$value" != "x" ]; then
        printf "value : %s\n" "$value"
    fi
done <"$1"

Test Input

$ cat dat/supervalue.txt
setSuperValue('sdfsdfd')
something else
setSuperValue('sdfsdfd')
something else
setSuperValue('sdfsdfd')
something else

Example Output

$  bash parsevalue.sh dat/supervalue.txt
value : sdfsdfd
value : sdfsdfd
value : sdfsdfd