Date: Fri, 18 Dec 2009 19:01:45 +0100 From: ocean <ocean_ieee@yahoo.it> To: Anton Shterenlikht <mexas@bristol.ac.uk> Cc: glarkin@freebsd.org, perryh@pluto.rain.com, freebsd-questions@freebsd.org Subject: Re: editing a binary file Message-ID: <4B2BC389.7040106@yahoo.it> In-Reply-To: <20091218165627.GB89667@mech-cluster241.men.bris.ac.uk> References: <alpine.BSF.2.00.0912180904180.11293@lightning.wonkity.com> <20091218165627.GB89667@mech-cluster241.men.bris.ac.uk>
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Anton Shterenlikht wrote: > On Fri, Dec 18, 2009 at 09:33:49AM -0700, Warren Block wrote: >> perryh@pluto.rain.com wrote: >>> Greg Larkin <glarkin@freebsd.org> wrote: >>>> ... >>>>> truncate -4 myfile should get rid of the last four bytes. Maybe >>>>> there's a similar efficient way to truncate the start of a file. >>>> This should do it: >>>> >>>> dd if=oldfile of=newfile bs=1 skip=4 >>> Or, perhaps marginally more efficient: >>> >>> dd if=oldfile of=newfile bs=4 skip=1 >> It would be nice to avoid the file copy, but maybe there's no way to do >> that. The small buffer size for dd will probably make copies of >> multi-gig files slow. This might be faster: >> >> tail -c +5 myfile > outfile >> truncate -4 outfile >> >> (Has anyone mentioned that you can edit binary files interactively with >> vi yet? No? Well, it's horrific and surely has interesting failure >> modes. And there are probably disadvantages also.) > > Vim, yes. I tried, but failed. At the moment dd/truncate combination > seems the most appealing. But I'll look at C/perl/python proposed > solutions as well. > > many thanks >
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