Why regular expression doesn't match input with sed command

Question

I'd like to cut extra spaces from "ps aux" output and replace them with one space. What I do is:

ps axu | sed 's/[ ]+/ /g'

But output seems to be unchanged, I still get too much spaces between tokens.

username    4876 ... <the rest of columns ommitted>

Why this regular expression doesn't match empty space between username and pid?

score 2 · Accepted Answer · answered Dec 18 '17 at 13:21

2

Because sed uses basic regular expressions (BRE), and + isn't part of them. Use s/ */ / (two spaces in the pattern part), or -E for extended regular expressions in GNU or BSD sed: sed -E 's/ +/ /g'

answered Dec 18 '17 at 13:21

ilkkachu

138,973

Or use \{1,\}, the standard BRE equivalent of ERE +. – Stéphane Chazelas Dec 18 '17 at 14:51

Why regular expression doesn't match input with sed command

1 Answers1