Shell Tricks

A repository for useful bits and bobs I’ve found good at the shell prompt. Mostly in bash (Giffle:bash-shell).

Unpacking an RPM without installing it

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As I don’t have admin privileges at work, it’s handy to be able to unpack a binary RPM so I can use recent software without properly installing it. I was wanting to use wxPython, so I downloaded the RPMs and unpacked them in my home space:

rpm2cpio wxPython-common-gtk2-ansi-2.6.3.3-fc2_py2.3.i386.rpm > \
   wxPython-common-gtk2-ansi-2.6.3.3-fc2_py2.3.i386.cpio
cpio -idv < wxPython-common-gtk2-ansi-2.6.3.3-fc2_py2.3.i386.cpio 
rpm2cpio wxPython2.6-gtk2-ansi-2.6.3.3-fc2_py2.3.i386.rpm > \
   wxPython2.6-gtk2-ansi-2.6.3.3-fc2_py2.3.i386.cpio
cpio -idv < wxPython2.6-gtk2-ansi-2.6.3.3-fc2_py2.3.i386.cpio 

I could then twiddle with my PYTHONPATH and LD_LIBRARY_PATH so that python would see these new libraries, and so can now run wxPython apps at work. (Something like this, although I may has mis-remembered the paths). export PYTHONPATH=$HOME/usr/local/lib/python2.3/site-packages export LD_LIBRARY_PATH=$HOME/usr/local/lib

Gunzip and unTar over a pipe

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gzip -dc <filename>.tar.gz | tar -xvf -

Shell-script for acting on multiple files

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To execute a shell command on every file in a directory, as separate execs, we can use #!/bin/bash

for file in \`ls $1\`
do
echo eins;
cat header $1$file > /tmp/temp
cat /tmp/temp > $1$file
done
exit 0;

OR find ./ -name “*.ext” -exec chmod a+r {} ; but this works recursively.

Another quite nice thing, used for updating CVS/Root files on a Zaurus: find . -name Root | xargs cp newRoot Just copies the contents of newRoot into every Root file. I think this works too: find . -name Root | xargs ’echo [email protected]:/dir/root >' as long as the quote are used to avoid the initial interpretation of the >.

Slicing

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These pieces of randomness will look for all .sh files in PWD and print the 41st line of each - don’t ask me why I wanted to know. Thanks to Brian R for these. for f in *.sh; do sed -n ‘41p’ $f; done or ls *.sh | xargs -l sed -n ‘41p’

Perl One-Liners

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I’m always forgetting how these work, so here goes… To perform a regex replace on a set of files, I do stuff like this: perl -pi -e’s/ukqcd2/trumpton/’ find ./ -name Root perl -pi -e’s/@SHELL@/sh/’ find ./ -name Makefile

Just found a better way to do perl one-liners. You tend to get a command-line buffer overflow using the previous technique on some OSs. This works better: find . -name Makefile -exec perl -pi -e “s/e/f/g” {} ; find . -type d -exec chmod 755 {} ; The ; at the end must be escaped with a backslash.