Databases, Systems & Networks

At the command line, environmental variables are defined for the current shell and become inherited by any running command or process. They can determine anything from the default shell, the PATH, the users home directory, to the terminal emulation type, current working directory, where a history file is located, language and localization settings, and going further to include shell variables, which include everything from customizations to the bash prompt, colorized ls output, and changes to terminal appearance, to aliases, and much more.

Let’s walk through how to list environment and shell variables, and then how to set and add new environment variables at the command line of Mac OS X.

Displaying Current Environment & Shell Variables in Mac OS X

To quickly get a list of environmental variables, you can use the following command:

printenv

If you want to see a complete list of shell variables, the ‘set’ command can be issued as well:

set

The output of these commands can be lengthy so you may wish to pipe the output through the less or more commands.
Lire la suite…

Want to share your terminal over the web for demo, learning or collaboration purpose? Try these two applications to share your terminal as a web application.

Please note that accepting input from remote clients is dangerous for most commands. When you need interaction with the TTY for some reasons, consider starting following tools with tmux or GNU Screen and run your command on it. Use following tools with trusted parties or inside VM. Let us see how to install and use gotty and ttyd on a Unix-like system.

1. gotty

GoTTY is a simple command line tool that turns your CLI tools into web applications. It is written in go programming language.

Installation

You can install gotty on macOS using the brew command:
$ brew install yudai/gotty/gotty

Sample outputs:

Updating Homebrew...
==> Tapping yudai/gotty Cloning into '/usr/local/Homebrew/Library/Taps/yudai/homebrew-gotty'...
remote: Counting objects: 5, done.
remote: Compressing objects: 100% (5/5), done.
remote: Total 5 (delta 1), reused 2 (delta 0), pack-reused 0
Unpacking objects: 100% (5/5), done.
Tapped 1 formula (30 files, 22.7KB)
==> Installing gotty from yudai/gotty
==> Downloading https://github.com/yudai/gotty/releases/download/v1.0.1/gotty_darwin_amd64.tar.gz
==> Downloading from https://github-production-release-asset-2e65be.s3.amazonaws.com/40808571/c401bd34-7bd9-11e7-8
######################################################################## 100.0%
==> Caveats GoTTY! ==> Summary
? /usr/local/Cellar/gotty/v1.0.1: 3 files, 8.2MB, built in 1 minute

Another option for Linux or Unix like system is to type the following command if you have a go language dev setup installed:

$ go get github.com/yudai/gotty

Usage

The syntax is:

gotty command
$ gotty htop

Sample outputs:

2017/09/23 22:31:19 Server is starting with command: htop
2017/09/23 22:31:19 URL: http://127.0.0.1:8080/
2017/09/23 22:31:19 URL: http://[::1]:8080/
2017/09/23 22:31:19 URL: http://[fe80::1]:8080/
2017/09/23 22:31:19 URL: http://[fe80::1c3a:3312:311b:cca4]:8080/
2017/09/23 22:31:19 URL: http://192.168.225.106:8080/
2017/09/23 22:31:19 URL: http://[fe80::6c1b:58ff:fe8a:4e6e]:8080/
2017/09/23 22:31:19 URL: http://[fe80::526a:bad6:960f:369f]:8080/
2017/09/23 22:31:19 URL: http://10.8.0.2:8080/

Fire a browser and type the url:
http://127.0.0.1:8080/
OR from another computer in your LAN/VLAN:
http://192.168.225.106:8080/

Sample outputs:

Gif 01: gotty in action

For more info and documentation see gotty home page.

2. ttyd

ttyd is a simple command-line tool for sharing terminal over the web, inspired by GoTTY. It is built on top of Libwebsockets with C for speed. Works with macOS, Linux, FreeBSD, OpenWrt/LEDE, and MS-Windows oses.

Installation

If you are using macOS, run the following brew command:
$ brew install ttyd
Sample outputs:

Viveks-MacBook-Pro:~ veryv$ brew install ttyd
Updating Homebrew...
==> Auto-updated Homebrew!
Updated 1 tap (homebrew/core).
No changes to formulae.
 
==> Installing dependencies for ttyd: json-c, libwebsockets
==> Installing ttyd dependency: json-c
==> Downloading https://homebrew.bintray.com/bottles/json-c-0.12.1.sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring json-c-0.12.1.sierra.bottle.tar.gz
?  /usr/local/Cellar/json-c/0.12.1: 27 files, 156.2KB
==> Installing ttyd dependency: libwebsockets
==> Downloading https://homebrew.bintray.com/bottles/libwebsockets-2.2.1.sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring libwebsockets-2.2.1.sierra.bottle.tar.gz
?  /usr/local/Cellar/libwebsockets/2.2.1: 29 files, 4.2MB
==> Installing ttyd
==> Downloading https://homebrew.bintray.com/bottles/ttyd-1.3.3.sierra.bottle.tar.gz
######################################################################## 100.0%
==> Pouring ttyd-1.3.3.sierra.bottle.tar.gz
?  /usr/local/Cellar/ttyd/1.3.3: 6 files, 282.6KB

If you are using a Debian/Ubuntu Linux, run:
$ sudo apt-get install -y software-properties-common
$ sudo add-apt-repository ppa:tsl0922/ttyd-dev
$ sudo apt-get update
$ sudo apt-get install ttyd

Usage

The syntax is:
$ ttyd command
$ ttyd bash
Sample outputs:

[2017/09/23 22:57:32:9322] NOTICE: ttyd 1.3.3 (libwebsockets 2.2.0)
[2017/09/23 22:57:32:9323] NOTICE: tty configuration:
[2017/09/23 22:57:32:9323] NOTICE:   start command: bash
[2017/09/23 22:57:32:9323] NOTICE:   reconnect timeout: 10s
[2017/09/23 22:57:32:9323] NOTICE:   close signal: SIGHUP (1)
[2017/09/23 22:57:32:9323] NOTICE: Initial logging level 7
[2017/09/23 22:57:32:9323] NOTICE: Libwebsockets version: 2.2.0 [email protected]
[2017/09/23 22:57:32:9323] NOTICE: IPV6 not compiled in
[2017/09/23 22:57:32:9323] NOTICE: libev support not compiled in
[2017/09/23 22:57:32:9323] NOTICE: libuv support not compiled in
[2017/09/23 22:57:32:9324] NOTICE:  Threads: 1 each 256 fds
[2017/09/23 22:57:32:9325] NOTICE:  mem: platform fd map:  2048 bytes
[2017/09/23 22:57:32:9325] NOTICE:  Compiled with OpenSSL support
[2017/09/23 22:57:32:9325] NOTICE:  SSL disabled: no LWS_SERVER_OPTION_DO_SSL_GLOBAL_INIT
[2017/09/23 22:57:32:9326] NOTICE: Creating Vhost 'default' port 7681, 2 protocols, IPv6 off
[2017/09/23 22:57:32:9337] NOTICE:  Listening on port 7681
[2017/09/23 22:57:32:9338] NOTICE:  mem: per-conn:          568 bytes + protocol rx buf
[2017/09/23 22:57:32:9339] NOTICE:  canonical_hostname = Viveks-MacBook-Pro.local

Fire a web browser and type url:
127.0.0.1:7681
Sample session:

Gif. 02: bash-ttyd demo

For more info and docs see project home page.

An alias is nothing but the shortcut to commands. The alias command allows the user to launch any command or group of commands (including options and filenames) by entering a single word. Use alias command to display a list of all defined aliases. You can add user-defined aliases to ~/.bashrcfile. You can cut down typing time with these aliases, work smartly, and increase productivity at the command prompt.

More about aliases

The general syntax for the alias command for the bash shell is as follows:

Task: List aliases

Type the following command:

alias

Sample outputs:

alias ..='cd ..'
alias amazonbackup='s3backup'
alias apt-get='sudo apt-get'
...

By default alias command shows a list of aliases that are defined for the current user.

Lire la suite…

How to check file size in unix using wc command

The wc command shows the number of lines, words, and bytes contained in file. The syntax is as follows to get the file size:
wc -c /path/to/file
wc -c /etc/passwd
Sample outputs:

5253 /etc/passwd

You can easily extract the first field either using the cut or awk command:
wc -c /etc/passwd | awk '{print $1}'
Sample outputs:

5253

OR assign this size to a bash variable:

myfilesize=$(wc -c "/etc/passwd" | awk '{print $1}')
printf "%d\n" $myfilesize
echo "$myfilesize"

How to get the size of a file in a bash script using stat command

The stat command shows information about the file. The syntax is as follows to get the file size on GNU/Linux stat:
stat -c %s "/etc/passwd"
OR
stat --format=%s "/etc/passwd"
To assign this size to a bash variable:

myfilesize=$(stat --format=%s "/etc/passwd")
echo "$myfilesize"
## or ##
myFileSizeCheck=$(stat -c %s "/etc/resolv.conf")
printf "My file size = %d\n" $myFileSizeCheck

The syntax is as follows to get the file size on BSD/MacOS stat:
stat -f %z "/etc/passwd"
Please note that if the file is symlink you will get size of that link only with the stat command.

du command example

The syntax is

du --apparent-size --block-size=1  "/etc/passwd"
fileName="/etc/hosts"
mfs=$(du --apparent-size --block-size=1  "$fileName" | awk '{ print $1}')
echo "$fileName size = ${mfs}"

Sample outputs from above commands:

Fig.01: How to check size of a file using a bash/ksh/zsh/sh/tcsh shell?

Find command example

The syntax is:

find "/etc/passwd" -printf "%s"
find "/etc/passwd" -printf "%s\n"
fileName="/etc/hosts"
mysize=$(find "$fileName" -printf "%s")
printf "File %s size = %d\n" $fileName $mysize
echo "${fileName} size is ${mysize} bytes."

You can use standard Unix commands such as sed, awk, grep, Perl, Python and more to get domain name from URL. No need to write regex. It is pretty simple.

Let use see various commands and option to grab the domain part from given variable under Linux or Unix-like system.

Get domain name from full URL

Say your url name is stored in a bash shell variable such as $x:
x='https://www.dbsysnet.com/'
You can use the awk as follows:
echo "$x" | awk -F/ '{print $3}'
### OR ###
awk -F/ '{print $3}' <<<$x
Sample outputs:

www.dbsysnet.com

Extract domain name from URL using sed

Here is a sample sed command:
url="https://www.dbsysnet.com"
echo "$url" | sed -e 's|^[^/]*//||' -e 's|/.*$||'

Extract domain name from URL using bash shell parameter substitution

Another option is to use bash shell parameter substitution:

# My shell variable 
f="https://www.cyberciti.biz/faq/copy-command/"
 
## Remove protocol part of url ##
f="${f#http://}"
f="${f#https://}"
f="${f#ftp://}"
f="${f#scp://}"
f="${f#scp://}"
f="${f#sftp://}"
 
## Remove username and/or username:password part of URL ##
f="${f#*:*@}"
f="${f#*@}"
 
## Remove rest of urls ##
f=${f%%/*}
 
## Show domain name only ##
echo "$f"

Shell script example

A shell script to purge urls from Cloudflare by matching domain name part:

#!/bin/bash
zone_id=""
api_key=""
 
urls="$@"
bon=$(tput bold)
boff=$(tput sgr0)
c=1
[ "$urls" == "" ] && { echo "Usage: $0 url"; exit 1; }
 
clear
echo "Purging..."
echo
for u in $urls
do
     echo -n "${bon}${c}${boff}.${u}: "
     ## Get domain name ##
     d="$(echo $u | awk -F/ '{ print $3}')"
     ## Set API_KEY, Email_ID, and ZONE_ID as per domain ##
     case $d in
	     www.cyberciti.biz) zone_id="ID_1"; api_key="MY_KEY_1"; email_id="[email protected]";;
	     theos.in) zone_id="ID_2"; api_key="MY_KEY_2"; email_id="[email protected]";;
	     *) echo "Domain not configured."; continue;;
     esac
     ## Do it ##
     curl -X DELETE "https://api.cloudflare.com/client/v4/zones/${zone_id}/purge_cache" \
     -H "X-Auth-Email: ${email_id}" \
     -H "X-Auth-Key: ${api_key}" \
     -H "Content-Type: application/json" \
     --data "{\"files\":[\"${u}\"]}"
     echo
     (( c++ ))
done
echo