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Altered behavior of 'cut' command
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leifbk
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Location: Bærum, Norway

PostPosted: Tue Apr 15, 2008 8:24 pm    Post subject: Altered behavior of 'cut' command Reply with quote

I just noticed that the 'cut' command in the new coreutils versions has a subtly altered behavior. I've got a couple of scripts that used to read the file size like this:

Code:
$SIZE=`ls -l $ARCHIVE | cut -f5 -d' '`


Now I find that this command, instead of the file size, shows the group, in this case 'users'. An ls -l of the file shows that there are two spaces between the file attributes and the next field:

Code:
-rw-r--r--  1 leif users 2272635 apr 15 18:08 archive.sql.gz


From a little googling on the phenomenon, it seems like this was the way cut was intended to work. If you're using ' ' as delimiter, then it is a space, not just any whitespace. I've now changed my byte-extracting snippet to use awk instead of cut, as awk uses actual whitespace for field separators:

Code:
SIZE=`ls -l $ARCHIVE | awk '{print $5}'`


Hope that this may help someone.
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Earthwings
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PostPosted: Tue Apr 15, 2008 9:12 pm    Post subject: Reply with quote

While you're at fixing, replace $ARCHIVE with "$ARCHIVE" to ensure that it works with filenames containing e.g. spaces. Even better:
Code:
SIZE="$(test -e "${ARCHIVE}" && stat -c %s "${ARCHIVE}" || echo 0)"

This one uses stat instead of parsing ls and returns 0 if ARCHIVE isn't set properly.

Moved from Portage & Programming to Documentation, Tips & Tricks.
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leifbk
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PostPosted: Wed Apr 16, 2008 12:22 pm    Post subject: Reply with quote

Thanks for the tip, Earthwings. It's maybe a bit over the top for my humble personal database backup and restore scripts, but there are a couple of interesting points that I'll add to my toolbox. I've been working with *nix since 1992, and I'm still learning new things. Funny thing is that whatever weird and twisted command line snippet you'll post online, someone will come up with an even weirder -- and more elegant -- one. Where in the world did you pick up that "stat" thingy? 8O

I just discovered that it's actually the output of ls -l that has changed. On a Gentoo computer that still hasn't been updated with the new coreutils, I notice that there's only one space after the file attributes.
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steveL
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PostPosted: Thu Apr 17, 2008 12:14 pm    Post subject: Reply with quote

"Since the previous stable release, 6.9, there have been .. almost 500 change sets in coreutils proper.
That doesn't include the 1100+ change sets in gnulib." http://lists.gnu.org/archive/html/coreutils-announce/2008-01/msg00001.html

Ouch! This has hit other production users so it'd be good to quantify the changes that are messing people up, not that I have any light to shed right now.

btw Earthwings, I'd recommend using [[ -e $ARCHIVE ]] as [[ is easier to deal with same as $(..) and significantly more powerful. I appreciate it might have been to enforce the quoting thing, but ime it's better to get people to use [[ from the beginning.
http://wooledge.org:8000/BashFAQ/031 is useful to show people a hint of what they can do with [[ as opposed to [ or test.

Regards,
steveL.
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