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

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

 gzip -dc .tar.gz | tar -xvf -

Shell-script for acting on multiple files

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 user@machine.dom:/dir/root >'

as long as the quote are used to avoid the initial interpretation of the >.

Slicing

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

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.

 for i in *.wma ; do mplayer.exe -vo null -vc dummy -af resample=44100 -ao pcm -waveheader "$i"; mv audiodump.wav "`basename "$i" .wma`.wav";done