how to modify matches to a regular expression with sed or another tool?

Question

I need to manipulate text that's in a file. I need to append a right parenthesis – ) – after every number that's preceded by a comma – , – e.g.,

• ,4   ➜ ,4)
• ,15 ➜ ,15)

I am struggling to find the proper way to do this with sed. I tried the following, which works for 1 digit but can't seem to be extended to 2 digits (so it's fine for first line above but not the second):

sudo sed 's/,\([0-9]\)/,\1)/g' filename

So then I tried the following for 2 digits:

sudo sed 's/,\([0-9]([0-9]?\)/,\1)/g' filename

This didn't do anything - the file remained unchanged, though I did not receive an error message. What is the proper way to search for one required digit and a second optional digit and then move them both into the replacement text? I still need to accomplish this:

• ,15 ➜ ,15)

Any advice would be greatly appreciated.

Answer 1

You were almost there, try this:

sudo sed 's/,\([0-9]\{1,2\}\)/,\1\)/g' filename

Here in addition to your command i have just added \{1,2\} which matches the previous regex between one to two times i.e. from a minimum of one time to a maximum of two times.

\([0-9]\{1,2\}\) explained:

• [0-9] will match a single digit between 0 to 9
• {1,2} will match the previous regex from one to a maximum of two times. So, one match is a must and the second is optional (as you want)
• () will make a regex group so that we can reference it later.

• Also note that we have used '\' in front of all extended regex syntax so that they they don't get treated literally. We could have used the -r switch (extended regex) with gnu sed, in that case we could just write:

  sudo sed -r 's/,([0-9]{1,2})/,\1\)/g' filename
  

EDIT: If you want to match any number of digits (minimum one) after comma you can do:

sudo sed 's/,\([0-9]\{1,\}\)/,\1\)/g' filename

or more simply:

sudo sed 's/,\([0-9]\+\)/,\1\)/g' filename