How many spaces is a tab in Java, Rust, C++, Python, C#, Powershell, Golang, Javascript

How many spaces is a tab in Java, Rust, C++, Python, C#, Powershell, Golang, Javascript

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How many spaces is a tab in Java, Rust, C+,, Python, C#, Powershell, Golang, etc.

A tab is not made out of spaces. It is a tab, whether in Java, Python, Rust, or generic text file editing. It is represented by a single Unicode character, U+0009.

It does not generally mean “insert this many spaces here” either. It means “put the cursor at the next closest tab stop in the line”. What that means exactly depends on the context. On an old typewriter I had, a tab key would advance the roller to the next column that was a multiple of 10

That is pretty much the same function as the tab character does.

Just for reference, modern text editors have their tab stops set to either every 4 or every 8 characters. That doesn’t mean that 1 tab = 4/8 spaces, that means that putting in a tab will align the cursor with the next multiple of 4/8 columns

In mainstream IDEs you can set the tab key to insert a desired number of spaces instead of a tab character.

 The concept of tab independent of space is rarely used these days. In any case, what the character represents is decoupled from what the key does is decoupled from what the screen shows.

In many IDEs, the tab character inserts the required number of spaces to advance to the next tab line. This is often a default.

I imagine it’s a compromise between tab loving extremists and space advocates. The ideal whitespace character is a subject of intense debate among programmers.

Source: Quora

Git Cheat Sheet

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Find Useful Git commands in this Git Cheat Sheet.

  • Clone a project:
    git clone git_repo_url project_name
  • Switch to a branch locally:
    git checkout branch_name
  • Modify a file, then save and push it to remote repo in current branch
    git add path_to_file_modifeid/file_name
    git commit -m “Description of modification”
    git push
  • Get a new version of a file after modifying local version
    git checkout path_to_file_modified/file_modified
  • Get latest version of current branch
    git fetch
    git pull
    if you have local changes, you will be prompted to commit or stash them before pulling.
  • Create a new branch based on current branch and switch to it
    git checkout –b branch_name
  • Switch to master branch
    git checkout master
  • Merge branch_name to master
    git merge branch_name
  • Delete local branch
    git branch -d branch_name
  • Undo a merge or pull
    git reset –hard
  • Undo a commit locally and on the remote branch
    git reset –hard commit_id
    git push –force
  • Get remote url of a local branch
    git remote show origin

Source: https://git-scm.com

Script with hash tables on windows and Linux

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How to declare and write a script with hash tables on windows and linux

  • Hash tables with powershell on windows

    Declaration:
    $states=@{“Alberta” = “Calgary”; “British Columbia” = “Vancouver”; “Ontario” = “Toronto” ; “Quebec” = “Montreal”}

    Name
    _____
    Value
    _______
    Alberta Calgary
    British Columbia Vancouver
    Ontario Toronto
    Quebec Montreal

    Add new key-value in hashtable:
    $states.Add(“Manitoba”,”Winnipeg”)

    Remove key-value in hashtable:
    $states.Remove(“Manitoba”,”Winnipeg”)
    Change value in hashtable:
    $states.Set_Item(“Ontario”,”Ottawa”)
    Retrieve value in hashtable:
    $states.Get_Item(“Alberta”)
    Find key in hashtable:
    $states.ContainsKey(“Alberta”)
    Find Value in hashtable:
    $states.ContainsValue(“Calgary”)
    Count items in hashtable:
    $states.Count
    Sort items by Name in hashtable:
    $states.GetEnumerator() | Sort-Object Name -descending
    Sort items by Value in hashtable:
    $states.GetEnumerator() | Sort-Object Value -descending

  • Hash tables with perl on linux or windows

     
    Declaration:
    my %hash = (); #Initialize a hash
    my $hash_ref = {}; # Initialize a hash reference. ref will return HASH
    Clear (or empty) a hash
    for (keys %hash)
    {
    delete $hash{$_};
    }
    Clear (or empty) a hash reference
    for (keys %$href)
    {
    delete $href->{$_};
    }
    Add a key/value pair to a hash
    $hash{ ‘key’ } = ‘value’; # hash
    $hash{ $key } = $value; # hash, using variables
    Using Hash Reference
    $href->{ ‘key’ } = ‘value’; # hash ref
    $href->{ $key } = $value; # hash ref, using variables
    Add several key/value pairs to a hash
    %hash = ( ‘key1’, ‘value1’, ‘key2’, ‘value2’, ‘key3’, ‘value3’ );
    %hash = (
    key1 => ‘value1’,
    key2 => ‘value2’,
    key3 => ‘value3’,
    );

    Copy a hash
    my %hash_copy = %hash; # copy a hash
    my $href_copy = $href; # copy a hash ref
    Delete a single key/value pair
    delete $hash{$key};
    delete $hash_ref->{$key};

  • Hash tables with python on linux or windows

    Hash tables are called dictionary in python.
    Declaration:
    dict = {‘Name’: ‘Zara’, ‘Age’: 7, ‘Class’: ‘First’}
    Accessing Values
    print “dict[‘Name’]: “, dict[‘Name’]
    print “dict[‘Age’]: “, dict[‘Age’]
    Output:
    dict[‘Name’]: Zara
    dict[‘Age’]: 7
    Updating Dictionary
    dict = {‘Name’: ‘Zara’, ‘Age’: 7, ‘Class’: ‘First’}

    dict[‘Age’] = 8; # update existing entry
    dict[‘School’] = “DPS School”; # Add new entry
    Delete Dictionary Elements
    #!/usr/bin/python

    dict = {‘Name’: ‘Zara’, ‘Age’: 7, ‘Class’: ‘First’}

    del dict[‘Name’]; # remove entry with key ‘Name’
    dict.clear(); # remove all entries in dict
    del dict ; # delete entire dictionary

Source:

  1. https://technet.microsoft.com/en-us/library/ee692803.aspx
  2. http://www.cs.mcgill.ca/~abatko/computers/programming/perl/howto/hash/
  3. http://www.tutorialspoint.com/python/python_dictionary.htm

How to pipe grep on command line on windows and Linux

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Let’s find how to pipe grep or find a specific string after running a command using shell, batch and powershell (windows and Linux)

  • On Linux via shell

    ls -al | grep filename

  • On Windows via powershell

    GetChildItem | Select-Object “filename”
    or
    GetChildItem | where-Object {$_ -match “filename”}

  • On Windows via batch

    Dir | findstr “filename”

reverse a string on Linux and Windows

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How to reverse a string on Linux and Windows

Via shell script on Linux

reverse a string on Linux and Windows

sh-3.2# vi reverse.sh
#### Start Script #####
#!/bin/bash
input_string=”$1″
reverse_string=””

input_string_length=${#input_string}
for (( i=$input_string_length-1; i>=0; i– ))
do
reverse_string=”$reverse_string${input_string:$i:1}”
done

echo “$reverse_string”
##### End Script #####

Let’s run it:

sh-3.2# chmod 775 reverse.sh
sh-3.2# ./reverse.sh Etienne
enneitE

Via powershell script on Windows

#Let’s use the script reverse.ps1 below.
######
$string=”Etienne”
$string_array=$string -split “”
[array]::Reverse($string_array)
$string_array -join ”

#####Output#####
PS C:\Users\etienne_noumen\Documents\Etienne\Scripting> .\reverse.ps1

E t i e n n e

enneitE

Via powershell script on Windows in one line

([regex]::Matches($String,’.’,’RightToLeft’) | ForEach {$_.value}) -join ”

Via batch script on Windows

::Note: ReverseStr also calls StrLen
::and string length is not greater than 80 chars
:: but can be changed.

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@echo off
SetLocal EnableDelayedExpansion
cls
set Str=Etienne
call :StrLen %Str%
echo Length=%Len%
call :ReverseStr %Str%
echo String=%Str%
echo Reverse Str=%Reverse%
exit /b

::—————-
:: Calc Var Length
::—————-
:: %*=Str to Check
:: Returns %Len%
:: —————
:StrLen %*
set Data=%*
for /L %%a in (0,1,80) do (
set Char=!Data:~%%a,1!
if not “!Char!”==”” (
set /a Len=%%a+1
) else (exit /b)
)
exit /b

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::—————
:: Reverse String
::—————
:: %* Str to Reverse
:: Returns %Reverse%
::——————
:ReverseStr %*
set Data=%*
call :StrLen %Data%
for /L %%a in (!Len!,-1,0) do (
set Char=!Data:~%%a,1!
set Reverse=!Reverse!!Char!
)
exit /b

Via perl script on Windows or Linux

Via python script on Windows or Linux

def reverse_string(a_string)
return a_string[::-1]
reverse_string(“etienne”) returns “enneite”
Source:

  1. http://www.computing.net/answers/programming/reverse-a-string-in-dos/26004.html

List only regular file names in a directory

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How to List only regular file names in a directory on Linux and Windows

Listing regular files in a directory without including . and .. files.


  • On Linux

    Solution 1:$ ls -p | grep -v /
    Solution 2: $ ls -F | grep -v ‘[/@=|]’
    Solution 3: $for list in `ls` ; do ls -ld $list | grep -v ^d > /dev/null && echo $list ; done ;
    Solution4:$ for list in `ls` ; do ls -ld $list | grep ^d > /dev/null || echo $list ; done ;
    Solution5 (exclude sym links):$ for list in `ls` ; do ls -ld $list | grep -v ^l > /dev/null && echo $list ; done ;


  • On Windows

    Solution 1: dir /a-d /b >..\File_List.txt

prompt and read input variables from keyboard

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Let’s find how to prompt and read input variables from keyboard while executing a script using shell, perl, python, batch and powershell (windows and Linux)

  • On Linux via shell

    read -p “Enter your name: ” name
    echo “Hi, $name. Let’s be friend!”

  • On Windows via powershell

    $name=read-host “Enter your name:”
    write-host “Hi $name, Let’s be friend!”

  • On Windows via batch

    Set /p Name=”Enter your name:”
    echo “Hi %name%, Let’s be friend!”

  • On Windows or Linux via perl

    print “Enter your name “;
    my $name = ;
    chomp $name; # Get rid of newline character at the end
    print “Hello $name, let’s be friend”;

  • On Windows or Linux via python

    name=input(“Enter your name: “)
    print (“Hello ” + name + ” let’s be friend”)

Replace all instances of a string in a file

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Shell script to replace all instances of a string in a file on Linux & Windows.

  • On Linux via bash script

    sed “s/$stringToReplace/$replaceWith/g” $File_Name > $File_Name

  • On Windows using Powershell

    ( get-content $File_Name ) | % { $_ -replace $stringToReplace, $replaceWith } | set-content $File_Name

  • On Windows using Batch

    set str=teh cat in teh hat
    echo.%str%
    set str=%str:teh=the%
    echo.%str%

    Script Output:
    teh cat in teh hat
    the cat in the hat

  • On Windows or Linux using Perl

    perl -pi.orig -e “s///g;”

  • On Windows or Linux using Python

Source:

  1. http://stackoverflow.com/questions/60034/how-can-you-find-and-replace-text-in-a-file-using-the-windows-command-line-envir

Search all files containing a specific string

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How to search all files containing a specific string on Linux and Windows?

  • On Linux

    grep -rnw ‘directory’ -e “pattern”
    grep –include=\*.{txt,log} -rnw ‘directory’ -e “pattern”
    This will only search for files with .txt or .log extension.
    grep –exclude=*.txt -rnw ‘directory’ -e “pattern”
    This will exclude files with .txt extensions.

  • On Windows

    CD Location
    FINDSTR /L /S /I /N /C:”pattern” *.log

Browse the internet via command line

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How to browse the internet via command line on Linux and Windows?

  • On Linux

    lynx http://google.ca
    If you don’t have lynx on your linux installation, you will have to install it. On Linux Red hat, install it like this:
    yum list lynx (to check the availability of the package)
    yum -y install lynx (to install the package)
    you can also use: curl -0 http://yoursite/index.html to get the source code of a specific file.

  • On Windows

    start /max http://google.ca
    Will open the url using your default browser.

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