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How can I match whitespace in sed? In my data I want to match all of 3+ subsequent whitespace characters (tab space) and replace them by 2 spaces. How can this be done?

218

The character class \s will match the whitespace characters <tab> and <space>.

For example:

$ sed -e "s/\s\{3,\}/  /g" inputFile

will substitute every sequence of at least 3 whitespaces with two spaces.


REMARK: For POSIX compliance, use the character class [[:space:]] instead of \s, since the latter is a GNU sed extension. See the POSIX specifications for sed and BREs

  • 4
    aha! It was the missing -e switch that got me. – sequoia mcdowell Sep 12 '11 at 14:44
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    I also had to add '-r' switch which enables extended regex's to make sed recognize '\s' as space. – HUB May 16 '12 at 15:12
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    With Apple's sed I had to use [[:space:]] because \s did not work for me. Perhaps \s is a GNU sed extension? – Jared Beck Jun 17 '13 at 23:24
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    @JaredBeck thanks, was running out of ideas why my simple regex wasnt working.. This is lame, I thought \s was standard extended regex.. Also -r doesnt work and -E did squat – Karthik T Sep 11 '13 at 4:58
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    Instead of [[:space:] one could use [[:blank:]] which does match horizontal tabs and spaces only (but no newlines, vertical tabs etc.). – stefanct Oct 13 '17 at 13:10
63

This works on MacOS 10.8:

sed -E "s/[[:space:]]+/ /g"
  • 2
    do you know if this works on all Linux distros ? – amphibient Feb 6 '14 at 17:26
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    Not generally, GNU sed won't have -E. From the BSD sed man page: "The -E, -a and -i options are non-standard FreeBSD extensions and may not be available on other operating systems." – Brad Koch Mar 18 '14 at 21:19
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    Why do you need the -E flag, for the + operator? Most expressions would probably be fine with * instead, then this would work on other platforms. – Samuel Mar 21 '15 at 0:05
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    @Samuel If you use *, the regex will match zero or more spaces, and you will get a space between every character, and a space at each end of each line. If you don't have the -E flag, then you want sed "s/[[:space:]]\+/ /g" to match one or more spaces. – jbo5112 Jan 20 '16 at 20:49
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    FWIW, NetBSD's sed supports the -E flag as well. – mcandre Dec 29 '17 at 21:53
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Some older versions of sed may not recognize \s as a white space matching token. In that case you can match a sequence of one or more spaces and tabs with '[XZ][XZ]*' where X is a space and Z is a tab.

  • 1
    So for the particular need here, with an older sed, you could do: $ sed 's/[XZ][XZ][XZ][XZ]*/ /g' inputfile where X is a tab and Z is a space. – Marnix A. van Ammers Apr 12 '10 at 15:08
10
sed 's/[ \t]*/"space or tab"/'
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    Is this guaranteed to work on any version of sed on any system? If not it might be worth mentioning where this does work in a similar fashion as the other answers, just so we know the limitations and where this might not have the intended result. – Mokubai Jul 22 '14 at 20:34
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    This RE is what I use to match whitespace. It is simpler than character classes just to match tab or space. It uses only the most basic conventions of regular expressions, so it should work anywhere with a functional implementation of regular expressions. – Nate Oct 18 '14 at 4:50
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    On Mac 10.9.5 this matches for spaces and 't'. I used Michael Douma's above to match whitespace chars (it also works with -e). – Alien Life Form Jul 31 '15 at 18:32
  • Doesn't work sensibly on my SUSE system. It matches the first place on the line where there is zero or more spaces, which is before the first character. I doubt that is the intended function, and certainly wasn't the requested use case. I believe you want to change the '*' for '\+' (or '\{3,\}' per the question) and maybe put a g at the end of the sed command to match all occurrences of the pattern. Replacing [ \t] with [[:space:]] may also be desirable as well, in case there is something else for whitespace in the line. – jbo5112 Jan 20 '16 at 20:59

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