Managing environment variables with modules

When dealing with different versions of a program (e.g. uclibc or glibc based cross compilers), you sometimes want to easily switch between them. In the past I used small env.sh files which contained the necessary additions to PATH and other environment settings. Because settings were never undone, this sometimes led to difficult to find problems.

When a former colleague showed me modules, these problems became a thing of the past: whenever I come to a situation were I previously wrote an env.sh or changed my .bashrc, I now write a modulefile. It’s a pity this software isn’t packaged inside debian (or I must have overlooked it). Therefore a quick installation guide:

wget http://heanet.dl.sourceforge.net/sourceforge/modules/modules-3.2.6.tar.bz2
tar xjvf modules-3.2.6.tar.bz2
cd modules-3.2.6
./configure
make
sudo make install


And add the following to your ~/.bashrc

. /usr/local/Modules/3.2.6/init/bash
module use ~/modules/


~/modules is the directory where I keep my modulefiles. For the codesourcery crosscompilers I currently have 2 files:

• cross-gcc/arm-2007q3-53-arm-none-eabi-i686-pc-linux-gnu
  
#%Module1.0
setenv ARCH arm
setenv CROSS_COMPILE arm-none-eabi-
prepend-path PATH /home/jan/no_backup/tools/arm-2007q3-53-arm-none-eabi-i686-pc-linux-gnu/arm-2007q3/bin/

• cross-gcc/arm-2007q3-51-arm-uclinuxeabi
  
#%Module1.0
setenv ARCH arm
setenv CROSS_COMPILE arm-uclinuxeabi-
prepend-path PATH /home/jan/no_backup/tools/arm-2007q3-51-arm-uclinuxeabi-i686-pc-linux-gnu/arm-2007q3/bin


Now I can use:

module avail
module load cross-gcc/arm-2007q3-51-arm-uclinuxeabi
module list
module unload cross-gcc


having fun with sed

I wanted to convert a whole bunch of scripts from a c-like syntax into python scripts. Along came sed…

cat > /tmp/convert.sed <<EOF
# Remove ; at end of line
s/;$//g

# Remove white space in front of lines (python indentation)
s/^[[:space:]]*//g

# Convert // styled comments to #
s+//+#+g

# Comment out /* styled comments */
\/\*/,/\*\// {
  s/^/# /g
}

# if else statements
# Not all statements work correctly yet, e.g.
# statements with "else" inside them (something_else();)
/^[^#]*else/,/}/ {
   s/ *else/else:/
   s/{//
   /else/! { s/}// }
   /else/! { s/^/   / }
}

/^ *if/,/}/ {
  s/if *(\(.*\))/if \1:/
  s/{//
  /if/! { /}/! { s/^/   / } }
  s/}//
}

# pythonify for loops
/^ *for/,/}/ {
   s/for *( *int *\(..*\) *= *\(.*\) *; *\1 *< *\(..*\) *; *\1++ *)/for \1 in range(\2,\3):/
   s/}//
   s/{//
   /for/! {
     s/^/   /
   }
}
EOF

cat > /tmp/example.c <<EOF
// Let's start with something simple
  some_line_with_space_before();

/*
 * here we do something different
 */
if(foo()) {
not_wel_indented_here();
} else {
foo();
}

for(int i = 0; i < 10; i++) {
  more_stuff(i);
}
EOF

sed -f /tmp/convert.sed < /tmp/example.c

It was the first time I needed block statements. It sure is a powerful language.

smiley in bash prompt

After the geekdinner of last Tuesday, I couldn’t resist creating my own blog.

As an appetizer, I’ll start with some code snippets I’ve found very usefull. For example the part of my .bashrc which configures the prompt:

smiley() {
    ret_val=$?
    if [ "$ret_val" = "0" ]
    then
        echo ":)"
    else
        echo ":( ($ret_val)"
    fi
}
Green="\033[0;32m"
Yellow="\033[1;33m"
Normal="\033[0m"
PS1="\[$Yellow\]\u@\h\[$Normal\]:\[$Green\]\w \$(smiley) \[$Normal\]"

I always use this because:

• the coloring makes it easy to see where my previous command started
• the smiley quickly shows me if and how the previous program exited