Shell script

Variable

NAME=$ID					# Will parse variables ID
NAME=AcTarjan				#$NAME=AcTarjan
NAME=hello world			# Will make mistakes , No spaces 
NAME="$ID world"			# Variables are parsed 
NAME="hello world"			# Spaces are allowed 
NAME='$ID world'			# Variables will not be resolved ,$ID Original output 
NAME=`pwd`					# The variable is equal to the result of the command execution output 

Regular expressions

Common operations

• Determine whether the directory exists

if [ ! -d $INSTALL_DIR ]; then
    echo "$INSTALL_DIR doesn't exist"
    exit
fi

• Judge whether the file exists

if [ -f "/data/filename" ];then
  echo " File exists "
else
  echo " file does not exist "
fi

• string matching

# regular expression 
if [[ $FILENAME =~ ^test.*zip$ ]];then
    echo "matched $FILENAME"
else
    echo "mismatched $FILENAME"
fi

• Traverse the directory

for file in `ls`
do
	echo $file
done