July 2010 - Roundtable

another shell thing I've forgotten...
by Adam Thompson 02 Aug '10

02 Aug '10

Inside a shell script, I want to start a persistent mysql client process and feed it commands one by one. I’d like to use a named pipe, but the only way I’ve found to do it so far is with a subshell, by putting 99% of the script inside the subshell and piping the subsell’s entire output to mysql. While this more-or-less works, it’s very much not ideal. If I use a named pipe, every time I echo something to that pipe (e.g. “echo INSERT INTO… > /tmp/mypipe”), mysql immediately exits upon reaching EOF, so only the very first command gets executed. I recall posting a way to accomplish this with psql & inetd a year or two ago, but I don’t want to use inetd – this *must* be entirely self-contained within a single shell script. Also I can’t figure out a way to tell mysql to ignore EOF on STDIN and to immediately reopen it. Anyone have any better ideas? Thanks, -Adam

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mount by label, a cautionary tail
by John Lange 21 Jul '10

21 Jul '10

I was migrating some data to some new disks and since the drive letters would be changing once the old disks were removed, I partitioned them and gave them label names. The original disks had labels like: boot srv tmp On the new disk I thought good names would be: /boot /srv /tmp (I think Redhat actually names things this way by default?) Anyhow, to make a long story short, mount by label ignores the leading slash. When the system rebooted, as predicted the drives came up in a different order so a "mount LABEL=srv" will actually mount the first disk named either "/srv" or "srv" which is obviously not good. I don't know if this is just a bug or intentional. -- John Lange http://www.johnlange.ca

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Request confirmation...
by Mike Pfaiffer 14 Jul '10

14 Jul '10

Someone we all know phoned me last night with some disturbing news. Unfortunately it doesn't pass the D.I.M.S. test (Does It Make Sense). He wanted some confirmation before "flying off the handle". He said he had a couple of clients phone up saying MTS was threatening Linux users with disconnection unless they switched to an all M$ environment. I said I'd pass along the request and see what people say. My suspicion is MTS is saying the same thing to Linux users as they are saying to Windows 2000 users. Namely a) Direct connections will no longer be supported with the next generation of MTS software (older software may still work). b) Tech support will be cancelled for that particular operating system. c) Although the problem with connection will be fixed with a router, the router MUST be purchased from MTS for maximum compatibility. d) They will not sell their routers to people running unsupported operating systems. e) Install techs will not be trained or permitted to connect machines with unsupported operating systems. OTOH, it could be a hoax. Time will tell... Later Mike

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script for file copy
by VE4ER / Andy 07 Jul '10

07 Jul '10

Can anybody suggest a script to copy files from one directory structure to another changing the filename in the process to include the original folder names, but only if an actual file with extension exists in the bottom child folder : Go from : Master Folder ------> Sub Folder1 -----> Sub Sub Folder1 ---> filename.example ------> Sub Folder2 -----> Sub Sub Folder1 ---> filename.example ------> Sub Folder2 -----> Sub Sub Folder2 ---> filename.example To: /Var/MainFolder/Master_Sub1_SubSub1_filename.example /Var/MainFolder/Master_Sub2_SubSub1_filename.example /Var/MainFolder/Master_Sub2_SubSub2_filename.example ....etc Thanks Andy

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Re: [RndTbl] script for file copy
by Adam Thompson 07 Jul '10

07 Jul '10

Umm... I think I misunderstood the original question. You want to flatten a directory structure into a single directory while preserving a record of the original path encoded in the filename. I think this would do what you want: find "${SRC}" -type f -print | while read F1; do F2=$( echo "${F1}" | tr '/' '_' ) mv "${F1}" "${F2}" done -Adam > -----Original Message----- > From: Adam Thompson [mailto:athompso@athompso.net] > Sent: Wednesday, July 07, 2010 2:09 PM > To: 'Continuation of Round Table discussion' > Subject: RE: [RndTbl] script for file copy > > I've had to do this before... there are some tools that'll do it for you, > essentially you want the UNIX version of MS-DOS's "UPDATE" command. > I would look at "rsync", used in local mode, use something like > > $ rsync -a --existing SRCDIR DSTDIR > > It is of course possible to do this in a shell script, but it's tricky to handle > the recursion correctly unless you use an iterative find/grep series, which > gets very expensive in terms of CPU time. > > The best non-recursive technique I can think of would be something like: > #!/bin/sh > SRC="$1" > DST="$2" > T1=$(mktemp) > T2=$(mktemp) > find "${SRC}" -type f -print | sed -e "s/^${SRC}//" | sort > "${T1}" > find "${DST}" -type f -print | sed -e "s/^${DST}//" | sort > "${T1}" > comm -12 "$T1" "$T2" | while read F ; do > cp "${SRCDIR}${F}" "${DSTDIR}${F}" > done > > -Adam > > > -----Original Message----- > > From: roundtable-bounces(a)muug.mb.ca [mailto:roundtable- > > bounces(a)muug.mb.ca] On Behalf Of VE4ER / Andy > > Sent: Wednesday, July 07, 2010 12:10 PM > > To: MUUG Roundtable > > Subject: [RndTbl] script for file copy > > > > Can anybody suggest a script to copy files from one directory > > structure to another changing the filename in the process to include > > the original folder names, but only if an actual file with extension > > exists in the bottom child folder : > > > > Go from : > > > > Master Folder ------> Sub Folder1 -----> Sub Sub Folder1 ---> > > filename.example > > ------> Sub Folder2 -----> Sub Sub Folder1 > > ---> filename.example > > ------> Sub Folder2 -----> Sub Sub Folder2 > > ---> filename.example > > > > > > To: > > > > /Var/MainFolder/Master_Sub1_SubSub1_filename.example > > /Var/MainFolder/Master_Sub2_SubSub1_filename.example > > /Var/MainFolder/Master_Sub2_SubSub2_filename.example > ....etc > > > > > > Thanks > > Andy > > > > _______________________________________________ > > Roundtable mailing list > > Roundtable(a)muug.mb.ca > > http://www.muug.mb.ca/mailman/listinfo/roundtable

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bash expansion question
by Adam Thompson 07 Jul '10

07 Jul '10

I can't find what I'm looking for in the bash(1) manpage, hoping there's an easy answer... I want to use a construct like for i in ~/path/*; do something $i && rm $i; done which works great as long as there are files in ~/path/. However, when the directory is empty, I get: rm: cannot remove `/home/athompso/path/*': No such file or directory which isn't quite what I want. The quick fix in this case is to use for i in ~/path/*; do [ -f $i ] && something $i && rm $i; done but once again, that strikes me as inelegant and I can't remember OR find the better way to do it. Anyone? Thanks, -Adam

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high-power 802.11g router recommendations?
by Adam Thompson 02 Jul '10

02 Jul '10

Looking for recommendations for a wireless router than has better-than-usual range. I’ve used the Buffalo WHR-HP-G54 with good results, but they’re basically impossible to find locally. I’ve also now experienced the D-Link DIR-825’s pathetic range, not sure I want to trust D-Link’s RangeBooster line without first-hand recommendations. Any suggestions? Thanks, -Adam

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Encrypt files/info/whatever easily.
by Sean Cody 01 Jul '10

01 Jul '10

So yeah this is normally something I would reserve for the newsletter but the inspiration hit me and I'll forget by September. :P So say someone wants to tell you something secret or you need to write down a secret in a file but don't want it in plaintext. Well using the shell & openssl [installed by default on OS X and probably on Linux [I know it's default on *BSD]]... Assuming your shell is SH derrivitive.. #cat << EOL | openssl aes-256-cbc -a -salt -out secret.txt OMG I haz a secretz! EOL (password will be requested here) # Notice I'm using what is referred to as a HEREDOC and piping it to openssl chosing the aes-256-cbc cipher. The -a parameter just says the input is in base64. -salt is well salting the cipher. So how do you get that back? #openssl aes-256-cbc -d -a -in secret.txt (password will be requested here) OMG I haz a secretz! # In this case -d is well... decrypt. You can replace the cat pipeline with -in somefile.txt if you want to do files themselves but this way no plaintext hits the disk (unless you shell swaps... which you have other issues then. :P). This is awesome because you don't have to install something special (ie. truecrypt) for a quick encrypt and you can store the data set anywhere and pull it (say via wget with pipelining) from random places with openssl installed to decrypt. Not really suggested for super secret stuff but it can be pretty handy... especially when passing around messages in a MacGyver sneaker net style situation. -- Sean

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