Databases, Systems & Networks

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

I want to find out how many times a word (say foo or an IP address) occurs in a text file using the grep command on Linux or Unix-like system?

You can use the grep command to search strings, words, text, and numbers for a given patterns. You can pass the -coption to grep command. It only shows the number of times that the pattern has been matched for each file.

Show the total number of times that the word foo appears in a file named bar.txt

The syntax is:
grep -c string filename
grep -c foo bar.txt
Sample outputs:

3

To count total number of occurrences of word in a file named /etc/passwd root using grep, run:
grep -c root /etc/passwd
To verify that run:
grep --color root /etc/passwd
Pass the -w option to grep to select only an entire word or phrase that matches the specified pattern:
grep -w root /etc/passwd
OR
grep -c -w root /etc/passwd
In this example only match a word being with root:
grep --color -w '^root' /etc/passwd
grep -c -w '^root' /etc/passwd
To show only the matching part of the lines.
grep -o 'root' /etc/passwd
grep -c -o 'root' /etc/passwd
Sample session:

Fig.01: Counting occurrence of words/strings using grep command

I want to display a countdown before purging cache from CDN network. Is there an existing command to show a conuntdown from 30..1 as 30,29,28,…1 on Linux or Unix bash shell script?

There are various ways to show a countdown in your shell scripts. 

First define your message:
msg="Purging cache please wait..."
Now clear the screen and display the message at row 10 and column 5 using tput:
clear
tput cup 10 5
Next you need to display the message:
echo -n "$msg"
Find out the length of string:
l=${#msg}
Calculate the next column:
l=$(( l+5 ))
Finally use a bash for loop to show countdown:
for i in {30..01}
do
tput cup 10 $l
echo -n "$i"
sleep 1
done
echo
Here is a complete shell script:

#!/bin/bash
# Purpose: Purge urls from Cloudflare Cache
# Author: Vivek Gite {www.cyberciti.biz} under GPL v2.x+
# --------------------------------------------------------
# Set me first #
zone_id="My-ID"
api_key="My_API_KEY"
email_id="My_EMAIL_ID"
row=2
col=2
urls="$@"
countdown() {
        msg="Purging ${1}..."
        clear
        tput cup $row $col
        echo -n "$msg"
        l=${#msg}
        l=$(( l+$col ))
        for i in {30..1}
        do
                tput cup $row $l
                echo -n "$i"
                sleep 1
        done
}
# Do it
for u in $urls
do
     amp_url="${u}amp/"
     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}\",\"${amp_url}\"]}" &>/dev/null &&  countdown "$u"
 
done
echo

You can run it as follows:
./script.sh url1 url2

POSIX shell version

From this post:

countdown()
(
  IFS=:
  set -- $*
  secs=$(( ${1#0} * 3600 + ${2#0} * 60 + ${3#0} ))
  while [ $secs -gt 0 ]
  do
    sleep 1 &
    printf "\r%02d:%02d:%02d" $((secs/3600)) $(( (secs/60)%60)) $((secs%60))
    secs=$(( $secs - 1 ))
    wait
  done
  echo
)

It can be run as follows:
countdown "00:00:10" # 10 sec
countdown "00:00:30" # 30 sec
countdown "00:01:42" # 1 min 42 sec