on 07-Feb-2019 (Thu)

ulimit -a

^^ note the use of the ulimit built-in shell command

^^^ note the -a flag to list all the resource limits, you can also look at individual ones with other flags

unset x

^^ note that unset is a shell built-in command

set -u

^^ use the set built-in command, at top of script.

^^^ note the u stands for unset (i.e. you are enabling guarding against unset variables)

In linux, in shell scripts, conditions for if statement can be checked using the test command, as below

if test 4 -gt 2; then
   echo "4 is bigger than 2"
fi

But there is a more syntatically elegent/common way to write the above, what is it? And think of the real point behind this buboflash question!

if [ 4 -gt 2 ]; then
   echo "4 is bigger than 2"
fi

^^ really what this question is demonstrating is that the if statement has as its condition, just some command that either returns success (0) or fail (non-zero) error code and that determines whether the if clause is executed! And the "[ ]" syntax is just a better looking replacement for the test command!

diff -r test1 test2

^^ note the -r for doing recursive check of all files in all subdirectories.

How to get bar out of cagingIt using destructuring?

let cagingIt = {
  foo: {
    bar: 'Nick Cage'
  }
};

let { foo: {bar: name} } = cagingIt;

console.log(name); // "Nick Cage"

In this example, foo is referring to the property name "foo". Following the colon, we then use barwhich refers to the property "bar". Finally, name acts as the variable storing the value.

Consider that destructuring is not null-safe so it is risky to use this way.

How to get the counts out of cagingIt as ct1, ct2, ct3 using destructuring in javascript?

let cagingIt = {
      foo: {
        bar: 'Nick Cage',
        counts: [1, 2, 3]
      }
    };

let { foo: {counts: [ ct1, ct2, ct3 ]} } = cagingIt;
console.log(ct2); // prints 2

In this example, foo is referring to the property name "foo".
Following the colon, we then use counts which refers to the property "counts".

Then use array destructuring and store those values as well.

Consider that destructuring is not null-safe so it is risky to use this way.

With Verdaccio, you can:

• Use private packages
• Cache npmjs.org registry
• Override public packages

find . -name '*.py'

^^ note the use of -name flag

^^^ note the use the shell pattern *.py (note this is globbing not regex syntax).

^^^^ note the pattern is provided within single quotes, if it was full name of file, then you don't need the quotes but for patterns you do

It takes strings from stdin (mostly via pipe, where another commands output is xargs' stdin), and it seperates the strings by whitespace (mostly linebreaks), and then gives those strings, one by one as command line arguments to another command (for example to find, rm, touch, etc).

e.g. find . -name '*.py' | xargs touch
^^ above will change the update timestamp of all python files in all subdirectories below current one, to current timestamp

In linux, complete the following command that finds all python files in current directory (and subdirectories below) and deletes them:

find . -name '*.py' [...]

find . -name '*.py' | xargs rm

^^ note the use of xargs (i.e. how xargs takes all the output from find, seperates it by whitespace/newline, and feeds it to the rm command, one by one, as command line args)

find . -name '*.py' | xargs grep 'username'

^^ note the user of find to locate all the python files, and how the glob pattern *.py is within single quotes

^^^ note the use of xargs (i.e. how xargs takes all the output from find, seperates it by whitespace/newline, and feeds it to the grep command, one by one, as command line args)

^^^^ note that output will have name of file, along with the line that has the 'username' regex pattern

In linux, if you want to use the awk command (which is the interpreter for the GAWK/AWK language), you use the following format (be very specific with the syntax):

awk [...] [...] <-- looking for two different occulsions

awk 'program' file(s)

^^ note that the program is in single quotes!!!

^^^ note that the file could be stdin (mostly supplied via pipe, e.g. ls -l | awk '{print $9}'

In linux, awk usually uses whitespace for delimitar by default, when processing a file, how can you change the delimitar? For example, if procssing /etc/passwd, that uses : as delimiter:

awk [...] '{print $1}' /etc/passwd

-F :

^^ note that the F here is short for FS (field seperator)

In linux, use awk to just display the file name, followed by space followed by file size of file in current directory. Note the output of running "ls -lh":

-rw-rw-r-- 1 kevin kevin 8.8K Nov 16 11:28 java_versions_all_instances.xlsx
-rw-r--r-- 1 kevin kevin 6.3K Nov  9 17:24 java_versions_detailed.xlsx

ls -lh | awk '{print $9 " " $5}'

^^ note the program given to the awk interpretor is wrapped in single quotes

^^^ note that the program block is wrapped in brace brackets

^^^ for the print method of AWK, note that concatenation is done via white-space seperated strings

bc

^^ note bc stands for basic calculator