ouyi

$ sudo keytool -storepass changeit -import -file /tmp/root.crt -noprompt -alias my-trusted-ca -keystore /Library/Java//JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/security/cacerts
Password:
Certificate was added to keystore

// changeit is the Java default keystore password

$ keytool -storepass changeit -list -keystore /Library/Java//JavaVirtualMachines/jdk1.8.0_92.jdk/Contents/Home/jre/lib/security/cacerts | grep my-trusted-ca
my-trusted-ca, Apr 11, 2018, trustedCertEntry,

ouyi

import java.lang.management.ManagementFactory;
import java.lang.management.RuntimeMXBean;
import java.util.List;

public class PrintJvmOptions {
    public static void main(String[] args) {
        RuntimeMXBean runtimeMxBean = ManagementFactory.getRuntimeMXBean();
        List<String> options = runtimeMxBean.getInputArguments();
        for(String o : options) {
            System.out.println(o);

ouyi

go to file begin/end:
fn + cmd + <-/->

file structure popup:
fn + cmd + F12

search everywhere:
shift shift

search for classes:

ouyi

image_id="$1"
for i in $(docker images -q); do 
    docker history $i | grep -q "$image_id" && echo $i; 
done | sort -u

ouyi

top # list processes, shift+p to sort processes by CPU usage
top -H -p <pid> # list threads, shift+p to sort threads by CPU usages
printf "%x\n" <tid> # convert tid to hexadecimal, called nid
jstack -l <pid> | grep -i <nid> -A 15 # get stack trace of the thread

ouyi

cat >> input.txt
hello
world
world
<ctrl+D>

wget https://raw.githubusercontent.com/ouyi/tez-demo/master/src/test/resources/input.txt
hadoop fs -copyFromLocal input.txt /tmp/

ouyi

# Remove trailing whitespaces using sed 
sed -i 's/[ \t]*$//' input_file

# Append line after pattern matching
sed -i "/mypattern.*/a 'my new stuff'" input_file

# Print the 2nd line
sed -n '2p' input_file

# Remove the last line

ouyi

# Update commit comments before the push
git commit -m "Fix an issue"
git commit -m "Fix an important issue" --amend

# Throw away all changes on local master and to have it exactly the same as origin/master:
git checkout master
git reset --hard origin/master

# Force origin/master to be the same as local master (dangerous!!!):

ouyi

# --- Join strings ---
function join_by { local IFS="$1"; shift; echo "$*"; }
# join_by ',' foo bar baz
# https://serverfault.com/questions/311856/portable-unix-way-to-join-strings-with-separator

echo -e "a\nb\nc" | tr '\n' ',' | sed 's/,$//g' # a,b,c

# --- Misc ---

# Retrieve the directory where the current script is in

ouyi

// java 8 test whether a nullable String is empty or not

if (Optional.ofNullable(s).orElse("").isEmpty()) {
    // s is null or empty
}