Sed: replace particular one/two digit(s)

Question

I have data in a table. And in one column I need to replace some indices (numbers from 1 to 23) to 3-4 digits sample numbers like: 2347,3856 etc.

So the original column looks like:

SF=1,2
SF=12,7
SF=17,4

And the output should be:

SF=2347,3856
SF=8553,9539
...

The problem is: if I do it for one sample (1->2720) it's fine; but then replacing 2 with something will create a mess etc., and I don't see how can I specify that the number should be replaced if only it's a single(two) digit for example? There could be more than 2 numbers in a row.

Sorry if it sounds confusing. I'm a beginner.

Update. Thanks fo mgjk I succeeded partially. But for some reason the new line is created after the first replacement in a row and then the next number is not replaced obviously. So what I get is:

SF=2347

,2

SF=8553

,7

And here is the code:

'sed "s/=${index},/=${sample},/g; s/,${index} /,${sample} /g; s/,${index},/,${sample},/g" samples.txt'

Why does it happen?

Answer 1

I think, you're trying to do something like this:

$ sed 's/=1,/=2347,/g; s/=12,/=3856,/g' sedtest.txt
SF=2347,2
SF=3856,15
SF=17,4

Including the literal '=' and ',' in your pattern and replacement string would let you distinguish between a "=1," and an "=12,"

---

Update:

To replace both variables, in sed, you can use a $ to match the end of the line.

$ sed 's/=1,/=2347,/g; s/=12,/=3856,/g; s/,2$/,2342/g; s/,15$/,234325/g' sedtest.txt
SF=2347,2342
SF=3856,234325
SF=17,4

It's going to look weird when you have bash variables like ${var} mixed in, but it should work, provided you use double-quotes:

e.g.,

$ a=42
$ sed "s/=1,/=2347,/g; s/=12,/=${a},/g; s/,2$/,2342/g; s/,15$/,234325/g" sedtest.txt
SF=2347,2342
SF=42,234325
SF=17,4

As an aside, if your replacements are huge, you can clean all this up using files in sed. E.g,

$ cat ./datascript.sed 
# Sed script to do stuff
s/=1,/=2347,/g
s/=12,/=2342,/g
s/,2$/,2342/g
s/,15$/,234325/g

Then run the file against the data

$ sed -f datascript.sed sedtest.txt
SF=2347,2342
SF=2342,234325
SF=17,4

The downside to the files is that I don't know any way to use variables in them.