I want to
(1) replace multiple numbers in a line for different values. For example, in the string "uncertainty = { 0.01 , 0.01 }" it should substitute for
string "uncertainty = { 0.2 , 0.2 }".
The problem is that
(2) these lines appear in hundreds of files with different quantities of numbers inside the brackets.
It could be
"uncertainty = { 0.1 , 0.1, 0.1 }", for "uncertainty = { 0.3 , 0.3, 0.3 }" or
"uncertainty = { 0.1 , 0.1, 0.1 , 0.1, 0.1, 0.1}", for
"uncertainty = { 0.3 , 0.3, 0.3 , 0.3, 0.3, 0.3}
and so on, and I have to substitute all of them.

I could not see how sed could be used to do that.

Use regular expressions. Convert one item inside the curly brackets into a regular expression such as:

[0-9].[0-9]1

What this expression means is "a number, a period, a number, a one". If the format is consistent through-and-through, this will only replace instances of "0.01" when put through sed.

There are other tools that would meet these needs as well, such as awk and tr, but you would still use regular expressions for them as well. To replace numbers such as this in bulk, you could replace that "1" with another [0-9] or a [1-3] to specify numbers in the range of 1-3.

For more info on Regular Expressions see Rexegg. They greatly expand the usefulness of virtually all text manipulation utilities.

Again thanks a lot!! Your hint helped me find a solution.

I read about awk and it turned out to help half of my questions: to go through substrings of a string that matches a given string. Because awk have some limitations, I used sed
to clean up the mess, like this in which v1 and v2 are passed via a shell script that call this code

The awk part
{
found = match($0,"uncertainty")
i = 4
if (found) {
while ( i < NF){
if ($i = v1) {
$i = v2
}
i = i + 2
}
print " " $0
}
else
{
print $0
}
}

The shell part

!/bin/bash

Check if directory already exists,

!/bin/bash

Check if directory already exists,

bitSizeDir="$1"
value1="$2"
value2="$3"

_mydir="$(pwd)"
find $bitSizeDir/ -type f > Files;
while read line; do
folder=dirname "$line"
file=basename "$line"
if [ "$file" = "input.c" ] ; then
awk -v v1=$value1 -v v2=$value2 -f changeValues.awk $line > input.new
mv input.new $folder
cd $folder
rm $file
mv input.new input.c
sed -i '' "s/$3 , }/ } /g" input.c
cd $_mydir
fi
done < Files
rm Files