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

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

How many spaces is a tab in Java

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

How many spaces is a tab in Java

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.


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Source: Quora

Git Cheat Sheet

Find Useful Git commands in this Git Cheat Sheet.

Here is a basic Git cheat sheet:

git init – Initialize a new git repository

git clone [repository] – Clone an existing repository

git status – Check the status of your repository


git add [file] – Add a file to the repository

git commit -m "[message]" – Commit changes with a message

git push – Push changes to a remote repository


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git pull – Pull changes from a remote repository

git branch – Show the current branch

git branch [branch-name] – Create a new branch

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git checkout [branch-name] – Switch to a different branch

git merge [branch-name] – Merge a branch into the current branch

git log – Show the commit history

git diff – Show changes between commits

git reset --hard [commit] – Reset repository to a specific commit

git stash – Stash changes

git stash apply – Apply stashed changes

Please note that this is a basic cheat sheet and git has many more functionalities and options, it is worth reading the git documentation to learn more.

  • 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

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

A hash table, also known as a hash map, is a data structure that is used to store key-value pairs. It is an efficient way to store data that can be quickly retrieved using a unique key.

Here is an example of how to declare and write a script with a hash table in Python:

# Declare an empty hash table
hash_table = {}

# Add some key-value pairs to the hash table
hash_table[‘key1’] = ‘value1’
hash_table[‘key2’] = ‘value2’
hash_table[‘key3’] = ‘value3’

# Access a value using its key
print(hash_table[‘key2’]) # Output: “value2”


# Modify a value using its key
hash_table[‘key2’] = ‘new value’
print(hash_table[‘key2’]) # Output: “new value”

# Delete a key-value pair using the `del` statement
del hash_table[‘key1’]

# Check if a key is in the hash table using the `in` operator
print(‘key1’ in hash_table) # Output: False


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# Output: False

In this example, we declare an empty hash table using the {} syntax. We then add some key-value pairs to the hash table using the [] syntax. We access a value using its key, modify a value using its key, delete a key-value pair using the del statement, and check if a key is in the hash table using the in operator.

I hope this helps! Let me know if you have any questions.

    • Hash tables with powershell on windows

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

      Name
      _____
      Value
      _______
      AlbertaCalgary
      British ColumbiaVancouver
      OntarioToronto
      QuebecMontreal

      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’}

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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

How to pipe grep on command line on Windows and Linux?

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”

On both Windows and Linux, you can use the grep command in combination with the | (pipe) operator to filter the output of another command. The | operator takes the output of the command on the left and passes it as input to the command on the right.

Here is an example of how to use the grep command with the | operator on both Windows and Linux:

On Linux:

# List all the files in the current directory and filter the output to show only the files that contain the word "example"
ls | grep example

On Windows:


# List all the files in the current directory and filter the output to show only the files that contain the word "example"
dir | findstr example

In this example, the ls (Linux) or dir (Windows) command lists all the files in the current directory, and the grep (Linux) or findstr (Windows) command filters the output to show only the lines that contain the word “example”.

You can use the grep command with the | operator in combination with other command-line utilities to perform various tasks. For example, you can use the grep command to filter the output of the ps command to show only the processes that contain a particular string in their command line arguments.

# Show all the processes that contain the string "python" in their command line arguments
ps -aux | grep python

I hope this helps! Let me know if you have any questions.


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reverse a string on Linux and Windows

How to reverse a string on Linux and Windows

On Linux:

  1. Using the rev command: The rev command is a utility that reverses the lines of a file or the characters in a string. To reverse a string, you can use the echo command to pass the string to rev:
echo "string" | rev
  1. Using the sed command: The sed command is a powerful utility that can perform various text transformations. To reverse a string, you can use the sed command with the -r option and the 's/.*(.)/\1/g' expression:
echo "string" | sed -r 's/.*(.)/\1/g'
  1. Using the awk command: The awk command is a programming language that is used for text processing. To reverse a string, you can use the awk command with the {print} action:
echo "string" | awk '{print $1}'

On Windows:

  1. Using the powershell command: The powershell command is a shell that provides a command-line interface for Windows. To reverse a string, you can use the powershell command with the -C option and the '[System.Text.Encoding]::Unicode.GetString([System.Text.Encoding]::Unicode.GetBytes("string"))' expression:
powershell -C "[System.Text.Encoding]::Unicode.GetString([System.Text.Encoding]::Unicode.GetBytes("string"))"
  1. Using the cmd command: The cmd command is the command-line interpreter for Windows. To reverse a string, you can use the cmd command with the for loop:
cmd /c "for /L %i in (1,1,%len%) do @echo !string:~%len%-%i,1!"

These are some ways to reverse a string on Linux and Windows. There are other ways to achieve this, using different utilities or programming languages.

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:


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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

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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.

@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

::—————
:: 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

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

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

How to Replace all instances of a string in a file?

How to Replace all instances of a string in a file?

  1. Open the file in read mode using the open() function.
  2. Read the contents of the file into a string using the read() method.
  3. Use the replace() method to replace all instances of the target string with the new string.
  4. Open the file in write mode using the open() function.
  5. Write the modified string to the file using the write() method.
  6. Close the file using the close() method.

Here is an example code snippet:

How to Replace all instances of a string in a file?
How to Replace all instances of a string in a file?

This will replace all instances of old_string with new_string in the file file.txt.

# Open the file in read mode
with open(‘file.txt’, ‘r’) as f:
# Read the contents of the file into a string
contents = f.read()

# Replace all instances of the target string
contents = contents.replace(‘old_string’, ‘new_string’)


# Open the file in write mode
with open(‘file.txt’, ‘w’) as f:
# Write the modified string to the file
f.write(contents)

# Close the file
f.close()

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:


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  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

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

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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