I always feared shell scripts when I was in college. Always knew that it is very powerful if I use it properly, I never did.

Two days back, in I was trying to help one of my college junior to setup Qt4 and the environment to run it. I told him to follow this page. But Pradeepto said the idea of having another user is not so good. and he said:

Apr 30 00:48:21 pradeepto: you can even do make sure that as you changedirectories,

the env-vars are set automagically.

So, I tried to something like that, asked few questions on #bash about how to write a function with same name of a shell command and then call the actual shell command. So, got the shell-builtin-command 'builtin' which executes other shell builtins. Also asked lots of questions to Jace about shell programming :p

My target was, as I change my directory to any directory named 'pyqt4' or sub-directories under it all environment variables should change accordingly to run Qt4 or PyQt4 codes and in other directories the normal environment should stay to run Qt3 :)

The result in my .bashrc :

export tQTDIR="$QTDIR"

export tPATH="$PATH"

export tMANPATH="$MANPATH"

export tLD_LIBRARY_PATH="$LD_LIBRARY_PATH"

export tPKG_CONFIG_PATH="$PKG_CONFIG_PATH"

export tQTINC="$QTINC"

export tQTLIB="$QTLIB"

export eFlag=0changePath()

changePath()

{QTDIR="$tQTDIR"

PATH="$tPATH"

MANPATH="$tMANPATH"

LD_LIBRARY_PATH="$tLD_LIBRARY_PATH"

PKG_CONFIG_PATH="$tPKG_CONFIG_PATH"

QTLIB="$tQTLIB"

QTINC="$tQTINC"

export QTDIR PATH MANPATH LD_LIBRARY_PATH PKG_CONFIG_PATH QTINC QTLIB

}

cd ()

{

if [ "$#" -eq "0" ]

then

if [ "$eFlag" -eq "1" ]

then

changePath

export eFlag=0

fi

builtin cd

else

bname=`echo "$1"|grep pyqt4 `

if [ "${bname}" = "$1" ]

then

QTDIR=/home/kdedev/src/kde/qt-copy

PATH=$QTDIR/bin:$PATH

MANPATH=$QTDIR/doc/man:$MANPATH

LD_LIBRARY_PATH=$QTDIR/lib:$LD_LIBRARY_PATH

PKG_CONFIG_PATH=$QTDIR/lib/pkgconfig:$PKG_CONFIG_PATH

QTINC=$QTDIR/include

QTLIB=$QTDIR/lib

export QTDIR PATH MANPATH LD_LIBRARY_PATH PKG_CONFIG_PATH QTINC QTLIB

export eFlag=1

builtin cd "$1"

else

if [ "$1" = ".." ]

then

builtin cd "$1"

dname=`pwd`

bname=`echo "$dname"|grep pyqt4 `

if [ "$bname" != "$dname" ]

then

if [ "$eFlag" -eq "1" ]

then

changePath

export eFlag=0

fi

fi

else

if [ "$eFlag" -eq "1" ]

then

changePath

export eFlag=0

fi

builtin cd "$1"

fi

fi

fi

}

I think the code is not so much readable in my blog :)

Update: Pradeepto asked me to upload the code as a file, so here it is. Just copy paste the contents of this file into your $HOME/.bashrc .