Answer:

To do so, use the command:

#jps -mlvV

Answer:

To trap your script before exit, you can use the trap in bash, e.g.

#!/bin/bash

set -eu

function bye {
  echo "Good bye"
}

trap bye EXIT
sleep 1000 
# Quit the script by pressing Ctrl+C

Answer:

You should always start your bash shell script with the line set -eu

The meaning is:

1. -e: cause the script to exit if an error
2. -u: cause the script to exit if any variable is not set

Answer:

If you know Perl well, there is no need to use awk to do string processing such as string splitting, it is easy with Perl also, e.g.

# echo "foo,bar,k3"  | perl -F',' -lane 'print $F[1]'
bar

Answer:

In Python, if you want to assign a raw string without any character escape, you can use the following:

s = r'\\foo\\\bar'
print s

Answer:

Assume you have a CSV file like the following (only contain number)

1,2,3
2,3,4
3,4,5
...

How do you sum the nth column of this file? It is easy with the use of awk

e.g. Assume you want to sum the 2nd column:

# awk -F "," '{ sum += $2 } END { print sum }' test.txt

Answer:

It is not uncommon that people have abused the command `cat` for many purpose, e.g. file I/O redirection

cat data.txt | sed 's/foo/bar/s'

You can avoid the cat command by the following commands:

data.txt < sed 's/foo/bar/s'
sed 's/foo/bar/s' < data.txt

Both directions are okay.

In fact, when you better understand the usage of some commands, you might find out that redirection is completely not needed.

e.g.

sed 's/foo/bar/s' data.txt

Answer:

To echo single quote (using single quote only), you can try

# echo foo
foo
# echo \'''foo
'foo

Answer:

In Ruby, a class constant has a name starting with an uppercase character, e.g.

Foo = 'bar'
puts Foo

Where you try to re-define the constant, a warning message will be shown, e.g.

Foo = 'bar'
Foo = '123'

(irb):18: warning: already initialized constant Foo

Answer:

In Ruby, global variable has a name beginning with $, e.g.

$foo = 'bar'
puts $foo

In contrast, local variable has a name start with a lower case letter or an underscore character, e.g.

foo = 'bar'
puts foo