JavaScript snippets

bash_snippets.md

Bash useful and neat snippets

Ensure a process exist

# incomplete
ps -o pid -C ssh-agent|sed -n '2p'

Append to a file

echo 'zend_extension=xdebug.so' | tee -a /etc/php7/conf.d/xdebug.ini

or take commented content from a file, and paste it uncommented

cat /etc/php7/conf.d/xdebug.ini | sed 's/^;zend_extension/zend_extension/g' >> /etc/php7/conf.d/Z99_dev.ini

Ensure a command exist

command -v foobar >/dev/null 2>&1 || { echo >&2 "Required binary foobar not found. This script will not work. Aborting."; exit 1; }

Extract value from JSON API output

ETCD_VERSION=$(curl -s -L http://127.0.0.1:2379/version | python -c "import sys, json; print(json.load(sys.stdin)['etcdserver'])")

Ensure a script runs only as root

if test "$(id -g)" -ne "0"; then
  (>&2 echo "You must run this as root."; exit 1)
fi

Send to Standard Error Output

function stderr { printf "$@\n" >&2; }

Validate if number

function is_number(){
  is_number='^[0-9]+$'
  if [[ ! $1 =~ $is_number ]]; then
    return 1
  else
    return 0
  fi
}

Do the same complex command with incremental numbers

Imagine you want to get the IPv4 address of a number of machines. You know the names will be in sequence (e.g. 0..n) and you want to create a zone format.

seq 0 4 | awk '{printf "+short @192.168.0.3 node%d.local\n", $1}' | xargs -L1 dig 

Loop commands from array

declare -a IMAGES=(\
                  ubuntu:14.04 \
                  ubuntu:16.04 \
                   )

for image in "${IMAGES[@]}"; do
    docker pull $image
done

Create a file

With contents that contains variables

(cat <<- _EOF_
iface eth0:1 inet static
  address ${IPV4_INTERNAL}
_EOF_
) >> /etc/network/interfaces.d/eth0

As an iteration

use-case; you want to format an hosts file (or DNS zone file) based on a list of nodes where we assign a name and internal IP incrementally.

Desired output would be like this.

##########
192.168.0.10	node0	# cluster_member
127.0.1.1	node1	# cluster_member  self
192.168.0.12	node2	# cluster_member
192.168.0.13	node3	# cluster_member
192.168.0.14	node4	# cluster_member
192.168.0.15	node5	# cluster_member
192.168.0.16	node6	# cluster_member
192.168.0.17	node7	# cluster_member
192.168.0.18	node8	# cluster_member
192.168.0.19	node9	# cluster_member
192.168.0.20	node10	# cluster_member
##########

Here it is

# e.g. this hosts file would be for node1
NODE_NUMBER=1
# e.g. our cluster would have node names starting by this
NODE_NAME_PREFIX=node
# e.g. our cluster would have a maximum of 10 nodes... node0 to node9
NODE_COUNT_MAX=10
# e.g. this hosts file would list IP addresses in sequences starting by this
IPV4_INTERNAL_PREFIX="192.168.0."

LIST=""
for i in `seq 0 $NODE_COUNT_MAX`; do
  if [[ ! "${NODE_NUMBER}" = "${i}" ]]; then
    NODE_POS=$(printf %d $((${i} + 10)))
    IP="${IPV4_INTERNAL_PREFIX}${NODE_POS}"
    APPEND_CLUSTER_MEMBER=""
  else
    IP="127.0.1.1"
    APPEND_CLUSTER_MEMBER=" self"
  fi
  LIST+="${IP}\t${NODE_NAME_PREFIX}${i}\t# cluster_member ${APPEND_CLUSTER_MEMBER}\n"
done

# Append conditionnally to /etc/hosts only if last node is not found in the file
grep -q -e "${NODE_NAME_PREFIX}${i}" /etc/hosts || printf $"\n##########\n${LIST}##########\n" >> /etc/hosts

Rename many files

Add increment number, replace part of name

Input is a list of files with pattern similar to this

02.09.09_Something photo.jpg
02.09.10_Something else - a note.jpg
02.09.11_Another one.jpg

... (a few hundreds like this)

And we want out

001 Something photo.jpg
002 Something else - a note.jpg
003 Another one.jpg
...

Could be done like this

ls | cat -n | while read n f; do i=`printf '%03d' "$n"`; fn=`echo $f|sed -E 's/^[0-9\.]+_//g'`; mv "$f" "$i $fn"; done

Awk

Filter file with path names, truncate last parts

1. Have file with similar contents

File: example.txt

/foo/bar/bazz/buzz/bizz.jpg
/foo/bar1/bazz1/buzz1/bizz1.jpg
/foo/bar2/bazz2/buzz2/bizz2.jpg
/foo/bar3/bazz3/buzz3/bizz3.jpg

2. What we want out

/foo/bar/bazz
/foo/bar1/bazz1
/foo/bar2/bazz2
/foo/bar3/bazz3

3. Create path.awk with following contents

NOTICE the truncate=2, so we want to take the two last path parts off.

File: path.awk

BEGIN { truncate=2; print "Path Muncher\n" }
function join(array, start, end, result, i) {
  result = array[start]
  for (i = start + 1; i <= end; i++)
      result = result"/"array[i]
  return result
}
{
    split($0, arr, "/");
    end = length(arr) - truncate;
    print join(arr, 0, end, "/")
}
END { print "\n" }

4. Use

cat example.txt | awk -f path.awk
Path Muncher

/foo/bar/bazz
/foo/bar1/bazz1
/foo/bar2/bazz2
/foo/bar3/bazz3

More

• Getting data about files

mixing_bash_python.sh

#!/bin/bash

## UNFINISHED shell script
## Illustrate how to mix Python and Bash
## Hat tip to http://bhfsteve.blogspot.ca/2014/07/embedding-python-in-bash-scripts.html

ENDPOINT=https://api.enlightns.com
NAME=example.enlightns.info

set -e

command -v http >/dev/null 2>&1 || { echo >&2 "HTTPie Python CLI is required for this script to work. Aborting."; exit 1; }
command -v python >/dev/null 2>&1 || { echo >&2 "Python is required for this script to work. Aborting."; exit 1; }

if [[ -z ${EMAIL} ]]; then
  (>&2 echo "Missing EMAIL shell environment variable"; exit 1)
fi



function extract_data_from_json() {
    PYTHON_WHAT=$1 PYTHON_INPUT=$2 python - <<END
import sys, json, os;
selector = os.environ['PYTHON_WHAT']
json_data = json.loads(os.environ['PYTHON_INPUT'])
print(json_data[selector])
END
}



if [[ -z ${ENLIGHTNS_AUTHORIZATION_TOKEN} ]]; then

  if [[ -z ${ENLIGHTNS_PASSWORD} ]]; then
    read -p "EnlightNS account password for ${EMAIL}? " ENLIGHTNS_PASSWORD
  fi

  AUTH_REQUEST_CREDS="{\"email\": \"${EMAIL}\", \"password\": \"${ENLIGHTNS_PASSWORD}\"}"

## See enlightns docs
## http://enlightns-docs.readthedocs.io/en/latest/
##
## Get Authentication token
##
## echo '{"email": "[email protected]", "password": "foobar"}' |  http --verbose POST https://api.enlightns.com/api-token-auth/ Content-Type:application/json
##
## Expected outcome
##
## {"token": "JWT 0000.REDACTED.REDACTED-AGAIN"}
##

AUTH_REQUEST_TOKEN=$(echo $AUTH_REQUEST_CREDS|http -b POST ${ENDPOINT}/api-token-auth/ Content-Type:application/json)
TOKEN=$(extract_data_from_json "token" "${AUTH_REQUEST_TOKEN}")

(cat <<- STATUS
---------------------------------------------------------------
Authentication to ${ENDPOINT} successful
subsequent requests will be made with the following HTTP header

    Authorization: ${TOKEN}

To prefent re-authenticating, use ENLIGHTNS_AUTHORIZATION_TOKEN
shell environment variable.
---------------------------------------------------------------
STATUS
)
ENLIGHTNS_AUTHORIZATION_TOKEN=$TOKEN
fi

## UNFINISHED here.
http --verbose GET ${ENDPOINT}/user/record/ Content-Type:application/json "Authorization: ${ENLIGHTNS_AUTHORIZATION_TOKEN}"

##
## Output would look like
##
#HTTP/1.1 200 OK
#Allow: GET, HEAD, OPTIONS
#Connection: keep-alive
#Content-Language: en
#Content-Type: application/json
#Date: Thu, 27 Apr 2017 17:36:21 GMT
#Server: nginx
#Transfer-Encoding: chunked
#Vary: Accept, Accept-Language, Cookie
#X-Frame-Options: DENY
#
#[
#    {
#        "active": true,
#        "auth": null,
#        "content": "0.0.0.0",
#        "id": 11,
#        "is_free": false,
#        "name": "example.enlightns.info",
#        "owner": "[email protected]",
#        "ttl": 300,
#        "type": "A"
#    }
#]

snippets.js

// Get All Style tags in one string
var stylesheetsElementsString = ''; [...document.head.childNodes].filter(a => a.rel == 'stylesheet').forEach(a => stylesheetsElementsString += a.outerHTML);

// Remove all Stylesheet tags from head
[...document.head.childNodes].forEach(e => {if(e.rel === "stylesheet"){e.remove();}});

// Get All Script src in one string
var scriptTags = [...document.head.childNodes].filter(a => a.localName === 'script' && !!a.src).map(a => a.src).join("\n");


/**
 * toCamelCase('foo-bar') === 'fooBar'
 */
function toCamelCase(str) {
    var regex = /-([a-z])/g;
    if (str.match(regex).length < 1) {
        throw new Error('Invalid input "'+str+'", is not in kebab-case-format, as per '+regex.toString());
    }
    return str.replace(regex, function (g) { return g[1].toUpperCase(); });
}


/**
 * toKebabCase('fooBar') === 'foo-bar'
 */
function toKebabCase(str) {
    var regex = /[A-Z\\d]/g;
    if (str.match(regex).length < 1) {
        throw new Error('Invalid input "'+str+'", is not in camelCaseSeparator, as per '+regex.toString());
    }
    return str.replace(regex, function (g) { return '-'+g[0].toLowerCase(); });
}

var tests = {cases:[], subjects: {toCamelCase: toCamelCase, toKebabCase: toKebabCase}};
tests.cases.push(['toCamelCase', 'foo-bar-baz', 'fooBarBaz']);
tests.cases.push(['toCamelCase', 'bar-baz', 'barBaz']);
tests.cases.push(['toKebabCase', 'fooBarBaz', 'foo-bar-baz']);
tests.cases.push(['toKebabCase', 'bazBarBuzzBizzz', 'baz-bar-buzz-bizzz']);
tests.cases.forEach(function poorManTests(cur) {
    var methodName = cur[0],
        testClosure = tests.subjects[methodName] || null,
        input = cur[1],
        expected = cur[2];
    if (testClosure !== null) {
        var testRun = testClosure.call(null, input);
        if (testRun !== expected) {
            console.log('FAIL: Function call '+methodName+'("'+input+'"), we expected "'+expected+'", we got "'+testRun+'".');
        }
    }
});


/**
 * We want to make sure someInput object has at least the following keys
 */
var SomeConstructorClass = function SomeConstructorClassConstructor(someInput){
    var requiredArguments = ['foo', 'bar', 'baz'];
    for (var property in someInput) {
        if (someInput.hasOwnProperty(property)) {
            // Do other things
            requiredArguments.splice(requiredArguments.indexOf(property), 1);
        }
    }
    if (requiredArguments.length > 0) {
        throw new Error('SomeConstructorClass error, we have missing arguments: ' + requiredArguments.join(', '));
    }
};