1.Shell determines whether the file exists
#!/bin/sh myPath="/var/log/httpd/" myFile="/var /log/httpd/access.log" # The -x parameter here determines whether $myPath exists and whether it has executable permissions if [ ! -x "$myPath" ]; then mkdir "$myPath" be # The -d parameter here determines whether $myPath exists if [ ! -d "$myPath" ]; then mkdir "$myPath" be # The -f parameter here determines whether $myFile exists if [ ! -f "$myFile" ]; then touch "$myFile" be # Other parameters include -n, -n is to determine whether a variable has a value if [ ! -n "$myVar" ]; then echo "$myVar is empty" exit 0 be # Check if two variables are equal if [ "$var1" = "$var2" ]; then echo '$var1 eq $var2' else echo '$var1 not eq $var2' be Difference between -f and -e Conditional Logic on Files -a file exists. -b file exists and is a block special file. -c file exists and is a character special file. -d file exists and is a directory. -e file exists (just the same as -a). -f file exists and is a regular file. -g file exists and has its setgid(2) bit set. -G file exists and has the same group ID as this process. -k file exists and has its sticky bit set. -L file exists and is a symbolic link. -n string length is not zero. -o Named option is set on. -O file exists and is owned by the user ID of this process. -p file exists and is a first in, first out (FIFO) special file or named pipe. -r file exists and is readable by the current process. -s file exists and has a size greater than zero. -S file exists and is a socket. -t file descriptor number fildes is open and associated with a terminal device. -u file exists and has its setuid(2) bit set. -w file exists and is writable by the current process. -x file exists and is executable by the current process. -z string length is zero. Whether you use -s or -f makes a big difference!
2.Shell arithmetic operations
$[1+2] #value:3
`expr 1 + 2` #value:3
$((1 + 2)) #value:3
3. Traverse each line of data in the file
while read lines
do
echo $lines
done<filename#filename is the file name
4. Extract row data
Awk syntax: awk /pattern/{action} filename
Simple usage of awk
Get the data of the first, column of the file:
awk '{print $1}' filename
5. The display date format is yyyyMMdd
date +%Y%m%d
6. A simple example of Map sorting by key value
HashMap<String, String> map = new HashMap<String, String>();
map.put("2012-07-04", "2012-07-04");
map.put("2012-07-03", "2012-07-03");
map.put("2012-07-07", "2012-07-07");
map.put("2012-07-01", "2012-07-01");
Object[] key = map.keySet().toArray();
Arrays.sort(key);
for (int i = 0; i < key.length; i++) {
System.out.println(map.get(key[i]));
}