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If I had a string like 45mb ./aaaa/bbbb/cccc/dddd and I use a regex like [^\/]*\/ it will match 45mb ./aaaa/bbbb/cccc/

I only want it to match ./aaaa/bbbb/cccc/ but I can't figure out how to do it.

I want to specifically match/find all occurrences of "everything before a forward slash up to and including the slash" as I want to use sed to substitute the matches like in the below sed command but not losing the file size bit at the start.

sed -e 's/[^\/]*\//--/g

Hopefully that makes some sense. I tried look ahead/behinds but I don't know if that's the correct regex solution for this.

  • Is the format always filesize {space} filename? Maybe awk would suffice? |awk '{print $1}' – Tim Jul 26 '13 at 18:06
  • If you just want to exclude spaces add that: [^\/ ]. What is your ultimate goal? It sounds like you are doing some tricky filename parsing / formatting, and usually that's never a clean and easy task. – jw013 Jul 26 '13 at 18:51
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Since you clarified what you wanted in a comment to Gnouc's answer, here's a solution:

sed 's|[^ /]*/|--|g'

$ echo '45mb ./aaaa/bbbb/cccc/dddd' | sed 's|[^ /]*/|--|g'
45mb --------dddd

This will break if you have a trailing slash, or if the filepath you're passing to it contains any spaces. It would be pretty easy to script something a little more watertight, but it would involve more than a single line.


Here's one solution using capture groups:

sed -e 's|\([^ ]* \).*/\(.*\)|\1\2|'

I'm using |s as the separators because then I don't have to bother escaping the forward-slashes (but I would have to escape any |s in the pattern). AFAIK sed can have pretty much any character as a separator.

The first capture group \([^ ]* \) matches 'any number of any character except a blank space, followed by a blank space'. The .*/ matches 'any number of any characters, followed by a forward-slash', and the second group \(.*\) captures 'any number of any characters'.

Sed's regular expressions (and most regular expressions) are greedy by default, so .*/ will match the longest string that matches its pattern.

$ echo '45mb ./aaaa/bbbb/cccc/dddd' | sed 's|\([^ ]* \).*/\(.*\)|\1\2|'
45mb dddd

However, this will break if there is a trailing slash:

$ echo '45mb ./aaaa/bbbb/cccc/dddd/' | sed 's|\([^ ]* \).*/\(.*\)|\1\2|'
45mb 

This version will work even with a trailing slash, but will break if you have more than one:

sed -e 's|\([^ ]* \).*/\(.\)|\1\2|'

$ echo '45mb ./aaaa/bbbb/cccc/dddd/' | sed 's|\([^ ]* \).*/\(.\)|\1\2|'
45mb dddd/
$ echo '45mb ./aaaa/bbbb/cccc/dddd//' | sed 's|\([^ ]* \).*/\(.\)|\1\2|'
45mb /
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Here is solution using regex with perl:

$ echo '45mb ./aaaa/bbbb/cccc/dddd' | perl -ne 'print $1 if /(\.\/.*\/)/'
./aaaa/bbbb/cccc/    

And substitution:

$ echo '45mb ./aaaa/bbbb/cccc/dddd' | perl -ple 's/(\.\/.*\/)/--/'
45mb --dddd
  • Thank you for the answers but i dont think i explained the end goal well enough. I want to run find ./ -maxdepth 1 -type d -print0 | xargs -0 du -h --max-depth 1 | sed -e 's/[^\/]*\//--/g;' to print a dir hierarchy with depth represented by -- for every sub-folder and at the start i want the dir size. At the moment the find and du will print what i want, and the sed will replace the dirs with -- but it also chops off the dir size from the start which i want left intact. – Flo Woo Jul 27 '13 at 1:36
  • .. turns out sed doesn't support regex lookarounds so thats why i couldnt get it working. Accepting answer from Gnouc for perl example. The end solution was perl -ple 's/(?<=\/)[^\/]+\//--/g' thanks again – Flo Woo Jul 27 '13 at 10:47

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