junjizhi

NUM=$1

#equel to for (int i=1; i<num; i++) in c/c++, java
for i in $(seq 1 $NUM);
do 
  echo $i
done

junjizhi

if [ -e $DIR1 ] && [ -e $DIR2 ] || [ -e $DIR3 ] 
then 
  echo "do sth"
fi

junjizhi

#delete files or dirs whose name does not end with '.sh' in the current path
ls | grep -v '\.sh$' | xargs rm -r

#However, this way does not solve the problem that the path names that have spaces, for example, "cmp\ output"

#more robust version
#from http://stackoverflow.com/questions/4702577/need-a-shell-script-that-deletes-all-files-except-pdf
find . -maxdepth 1 -type f ! -iname '*.pdf' -delete

#if we need to delete the directories, too, then remove '-type f'

junjizhi

prepare1:
        if [ ! -e $(LINUX_TAR_NAME) ] ; \
        then \
                wget $(LINUX_TAR_SITE) ; \
        fi;
        tar -xf $(LINUX_TAR_NAME) && \