Coding Bash vs. Perl vs. Python (by Evan Liu)

Topics about string

String: Create multi-line string 


		  
		  

		  
Tasks:
1.Create a multi-line string
2.Print the string
		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. #1.Create a multi-line string

  2. read -r -d '' mstr <<'EOD'

  3. This is a string with muliple lines

  4. escaple exmaple: "hello\nworld!"

  5. Variable examples: $PS1, $SHELL, $USER, $$

  6. DIR=$(pwd)

  7. list or array examples: @list

  8. hash examples: %map

  9. EOD

  10. 

  11. #2.Print the string

  12. echo "\$mstr=$mstr"

  13. 

  14. 

  15. -------output----------



  1. #1.Create a multi-line string

  2. 

  3. #2.Print the string

  4. $mstr=This is a string with muliple lines

  5. escaple exmaple: "hello\nworld!"

  6. Variable examples: $PS1, $SHELL, $USER, $$

  7. DIR=$(pwd)

  8. list or array examples: @list

  9. hash examples: %map



                
  1. #1.Create a multi-line string

  2. my $mstr = <<'EOD';

  3. This is a string with muliple lines

  4. escaple exmaple: "hello\nworld!"

  5. Variable examples: $PS1, $SHELL, $USER, $$

  6. DIR=$(pwd)

  7. list or array examples: @list

  8. hash examples: %map

  9. EOD

  10. 

  11. #2.Print the string

  12. print "\$mstr=$mstr\n";

  13. 

  14. -------output----------



  1. #1.Create a multi-line string

  2. 

  3. #2.Print the string

  4. $mstr=This is a string with muliple lines

  5. escaple exmaple: "hello\nworld!"

  6. Variable examples: $PS1, $SHELL, $USER, $$

  7. DIR=$(pwd)

  8. list or array examples: @list

  9. hash examples: %map



                
  1. #1.Create a multi-line string

  2. mstr = r'''This is a string with muliple lines

  3. escaple exmaple: "hello\nworld!"

  4. Variable examples: $PS1, $SHELL, $USER, $$

  5. DIR=$(pwd)

  6. list or array examples: @list

  7. hash examples: %map'''

  8. 

  9. #2.Print the string

  10. print "mstr=%s\n"% mstr

  11. 

  12. -------output----------



  1. #1.Create a multi-line string 

  2. 

  3. #2.Print the string 

  4. mstr=This is a string with muliple lines

  5. escaple exmaple: "hello\nworld!"

  6. Variable examples: $PS1, $SHELL, $USER, $$

  7. DIR=$(pwd)

  8. list or array examples: @list

  9. hash examples: %map



              

             
            
 
          

          

		  

        
          

		  
String: Get the length of a string 

		  

		  
		  

		  
Tasks:
1.Assign a string to a variable
2.Get the length of the string
		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. #1.Assign a string to a variable

  2. name="Scarborough Fair"

  3. 

  4. #2.Get the length of the string

  5. echo ${#name}

  6. 

  7. -------output----------



  1. #1.Assign a string to a variable

  2. 

  3. #2.Get the length of the string

  4. 16



                
  1. #1.Assign a string to a variable

  2. $name="Scarborough Fair";

  3. 

  4. #2.Get the length of the string

  5. print length($name)."\n";

  6. 

  7. -------output----------



  1. #1.Assign a string to a variable

  2. 

  3. #2.Get the length of the string

  4. 16



                
  1. #1.Assign a string to a variable

  2. name="Scarborough Fair"

  3. 

  4. #2.Get the length of the string

  5. print len(name)

  6. 

  7. -------output----------



  1. #1.Assign a string to a variable 

  2. 

  3. #2.Get the length of the string 

  4. 16



              

             
            
 
          

          

		  

        
          

		  
String: Get a substring at a given index 

		  

		  
		  

		  
Tasks:
1.Assign a string to a variable.
2.Print 5 chars starting from index 6, the output should be "rough".
		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. #1.Assign a string to a variable.

  2. name="Scarborough Fair"

  3. 

  4. #2.Print 5 chars starting from index 6, the output should be "rough".

  5. echo "substr: ${name:6:5}"

  6. 

  7. -------output----------



  1. #1.Assign a string to a variable.

  2. 

  3. #2.Print 5 chars starting from index 6, the output should be rough.

  4. substr: rough



                
  1. #1.Assign a string to a variable.

  2. $name="Scarborough Fair";

  3. 

  4. #2.Print 5 chars starting from index 6, the output should be "rough".

  5. print "substr: ".substr($name,6,5)."\n";

  6. 

  7. -------output----------



  1. #1.Assign a string to a variable.

  2. 

  3. #2.Print 5 chars starting from index 6, the output should be "rough".

  4. substr: rough



                
  1. #1.Assign a string to a variable.

  2. name="Scarborough Fair"

  3. 

  4. #2.Print 5 chars starting from index 6, the output should be "rough".

  5. print "slicing:", name[6:11]

  6. 

  7. -------output----------



  1. #1.Assign a string to a variable. 

  2. 

  3. #2.Print 5 chars starting from index 6, the output should be "rough". 

  4. slicing: rough



              

             
            
 
          

          

		  

        
          

		  
String: Get index of a substring 

		  

		  
		  

		  
Tasks:
1.test1
2.Assign a string to a variable.
3.Print index of substring "rough".
4.Check if substring "rough" exists or not.
		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. #1.test1

  2. name="Scarborough Fair"

  3. 

  4. #2.Assign a string to a variable.

  5. x=${name%%rough*}

  6. echo -n "The index of 'rough' is: "

  7. [[ $x = $name ]] && echo -1 || echo ${#x}

  8. 

  9. #3.Print index of substring "rough".

  10. padding=`grep -q rough <<<"$name"|| echo not`

  11. echo "'rough' does $padding exist in string \"$name\""

  12. 

  13. -------output----------



  1. #1.test1

  2. 

  3. #2.Assign a string to a variable.

  4. The index of 'rough' is: 6

  5. 

  6. #3.Print index of substring rough.

  7. 'rough' does  exist in string "Scarborough Fair"



                
  1. #1.test1

  2. $name="Scarborough Fair";

  3. 

  4. #2.Assign a string to a variable.

  5. printf "The index of 'rough': %d\n", index($name,'rough');

  6. 

  7. #3.Print index of substring "rough".

  8. printf "'rough' does%s exist in string Scarborough Fair", ( index($name,'rough') == -1 )? " not": "";

  9. 

  10. -------output----------



  1. #1.test1

  2. 

  3. #2.Assign a string to a variable.

  4. The index of 'rough': 6

  5. 

  6. #3.Print index of substring "rough".

  7. 'rough' does exist in string Scarborough Fair



                
  1. #1.test1

  2. name="Scarborough Fair"

  3. 

  4. #2.Assign a string to a variable.

  5. #  get exception if none found with index()

  6. print "The index of 'rough':", name.index('rough') 

  7. print "The index of 'rough':", name.find('rough') 

  8. 

  9. #3.Print index of substring "rough".

  10. print "'rough' does "+ ('' if 'rough' in name else 'not') + "exist in string "+name

  11. 

  12. -------output----------



  1. #1.test1 

  2. 

  3. #2.Assign a string to a variable. 

  4. #  get exception if none found with index() 

  5. The index of 'rough': 6

  6. The index of 'rough': 6

  7. 

  8. #3.Print index of substring "rough". 

  9. 'rough' does exist in string Scarborough Fair



              

             
            
 
          

          

		  

        
          

		  
String: Replace a substring 

		  

		  
		  

		  
Tasks:
1.Assign a string to a variable
2.Replace 'Fair' with 'fair' for one occurrence
3.Replace 'Fair' with 'fair' for all occurrences
		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. #1.Assign a string to a variable

  2. name="Scarborough Fair Fair"

  3. 

  4. #2.Replace 'Fair' with 'fair' for one occurrence

  5. echo ${name/Fair/fair}

  6. 

  7. #3.Replace 'Fair' with 'fair' for all occurrences

  8. echo ${name//Fair/fair}

  9. 

  10. -------output----------



  1. #1.Assign a string to a variable

  2. 

  3. #2.Replace 'Fair' with 'fair' for one occurrence

  4. Scarborough fair Fair

  5. 

  6. #3.Replace 'Fair' with 'fair' for all occurrences

  7. Scarborough fair fair



                
  1. #1.Assign a string to a variable

  2. $name="Scarborough Fair Fair";

  3. 

  4. #2.Replace 'Fair' with 'fair' for one occurrence

  5. $name =~ s/Fair/fair/;

  6. printf $name."\n";

  7. 

  8. #3.Replace 'Fair' with 'fair' for all occurrences

  9. $name="Scarborough Fair Fair";

  10. $name =~ s/Fair/fair/g;

  11. printf $name."\n";

  12. 

  13. -------output----------



  1. #1.Assign a string to a variable

  2. 

  3. #2.Replace 'Fair' with 'fair' for one occurrence

  4. Scarborough fair Fair

  5. 

  6. #3.Replace 'Fair' with 'fair' for all occurrences

  7. Scarborough fair fair



                
  1. #1.Assign a string to a variable

  2. name="Scarborough Fair Fair"

  3. 

  4. #2.Replace 'Fair' with 'fair' for one occurrence

  5. print name.replace('Fair','fair', 1)

  6. 

  7. #3.Replace 'Fair' with 'fair' for all occurrences

  8. print name.replace('Fair','fair')

  9. 

  10. -------output----------



  1. #1.Assign a string to a variable 

  2. 

  3. #2.Replace 'Fair' with 'fair' for one occurrence 

  4. Scarborough fair Fair

  5. 

  6. #3.Replace 'Fair' with 'fair' for all occurrences 

  7. Scarborough fair fair



              

             
            
 
          

          

		  

        
          

		  
String: Capitalize a string 

		  

		  
		  

		  
Tasks:
1.Assign a string to a variable
2.Change the string to Upper case 
		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. #1.Assign a string to a variable

  2. name="Scarborough Fair"

  3. 

  4. #2.Change the string to Upper case 

  5. echo $name | tr '[:lower:]' '[:upper:]'

  6. echo $name | tr '[:upper:]' '[:lower:]'

  7. #  in awk

  8. echo $name | awk '{print toupper($0)}'

  9. echo $name | awk '{print tolower($0)}'

  10. #  in bash 4.0

  11. echo ${name^^}

  12. echo ${name,,}

  13. echo ${name^}

  14. 

  15. -------output----------



  1. #1.Assign a string to a variable

  2. 

  3. #2.Change the string to Upper case 

  4. SCARBOROUGH FAIR

  5. scarborough fair

  6. #  in awk

  7. SCARBOROUGH FAIR

  8. scarborough fair

  9. #  in bash 4.0

  10. SCARBOROUGH FAIR

  11. scarborough fair

  12. Scarborough Fair



                
  1. #1.Assign a string to a variable

  2. $name="Scarborough Fair";

  3. 

  4. #2.Change the string to Upper case 

  5. print uc($name)."\n";

  6. print lc($name)."\n";

  7. print ucfirst($name)."\n";

  8. print lcfirst($name)."\n";

  9. 

  10. 

  11. -------output----------



  1. #1.Assign a string to a variable

  2. 

  3. #2.Change the string to Upper case 

  4. SCARBOROUGH FAIR

  5. scarborough fair

  6. Scarborough Fair

  7. scarborough Fair



                
  1. #1.Assign a string to a variable

  2. name="Scarborough Fair"

  3. 

  4. #2.Change the string to Upper case 

  5. print name.upper()

  6. print name.lower()

  7. print name.capitalize()

  8. print name.title()

  9. 

  10. -------output----------



  1. #1.Assign a string to a variable 

  2. 

  3. #2.Change the string to Upper case  

  4. SCARBOROUGH FAIR

  5. scarborough fair

  6. Scarborough fair

  7. Scarborough Fair



              

             
            
 
          

          

		  

        
          

		  
String: Check if a variable is empty 

		  
In perl
Values are considered false if it equals '', (), [], {}, 0, 0L, 0.0, 0j, False, None

		  
		  

		  
Tasks:
1.Define a function to check if the input is an empty string
2.Call the function with different arguments
		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. #1.Define a function to check if the input is an empty string

  2. func1(){

  3. s=$1

  4. if [ "$s" ]; then e1=" not"; fi

  5. if [ "$s" != "" ]; then e2=" not"; fi

  6. if [ -n "$s" ]; then e3=" not"; fi

  7. if [ ! -z "$s" ]; then e4=" not"; fi

  8. echo "\$1 is$e1 empty"

  9. echo "\$1 is$e2 empty"

  10. echo "\$1 is$e3 empty"

  11. echo "\$1 is$e4 empty"

  12. }

  13. 

  14. #2.Call the function with different arguments

  15. 

  16. #2.Call the function with different arguments

  17. func1

  18. 

  19. #2.Call the function with different arguments

  20. func1 ""

  21. 

  22. #2.Call the function with different arguments

  23. func1 " "

  24. 

  25. -------output----------



  1. #1.Define a function to check if the input is an empty string

  2. 

  3. #2.Call the function with different arguments

  4. 

  5. #2.Call the function with different arguments

  6. $1 is empty

  7. $1 is empty

  8. $1 is empty

  9. $1 is empty

  10. 

  11. #2.Call the function with different arguments

  12. $1 is empty

  13. $1 is empty

  14. $1 is empty

  15. $1 is empty

  16. 

  17. #2.Call the function with different arguments

  18. $1 is not empty

  19. $1 is not empty

  20. $1 is not empty

  21. $1 is not empty



                
  1. #1.Define a function to check if the input is an empty string

  2. sub func1{

  3. $e1=$e2=1; #1 is true

  4. if(not defined $_[0]){ $e1=0 }

  5. if( $_[0] eq ""){ $e2=0 }

  6. print "argument ".(($e1)? "":"not ")."defined\n";

  7. print "argument ".(($e2)? "not ":"")."empty\n";

  8. }

  9. 

  10. #2.Call the function with different arguments

  11. func1();

  12. #  call with func1('')

  13. func1("");

  14. #  call with func1(' ')

  15. func1(" ");

  16. 

  17. 

  18. -------output----------



  1. #1.Define a function to check if the input is an empty string

  2. 

  3. #2.Call the function with different arguments

  4. argument not defined

  5. argument empty

  6. #  call with func1('')

  7. argument defined

  8. argument empty

  9. #  call with func1(' ')

  10. argument defined

  11. argument not empty



                
  1. #1.Define a function to check if the input is an empty string

  2. def func(p1):

  3.   print "It's "+("not " if p1 else "")+"empty"

  4.   print "It's "+("" if not p1 else "not ")+"empty"

  5. 

  6. #2.Call the function with different arguments

  7. #  ERROR: func() takes exactly 1 argument (0 given)

  8. #  func() 

  9. #  call with func('')

  10. func('')

  11. #  call with func(' ')

  12. func(' ')

  13. 

  14. -------output----------



  1. #1.Define a function to check if the input is an empty string 

  2. 

  3. #2.Call the function with different arguments 

  4. #  ERROR: func() takes exactly 1 argument (0 given) 

  5. #  func()  

  6. #  call with func('') 

  7. It's empty

  8. It's empty

  9. #  call with func(' ') 

  10. It's not empty

  11. It's not empty



              

             
            
 
          

          

		  

        
          

		  
String: Remove leading and tailing whitespaces 

		  
Note: Ip perl, chomp() function will remove current value of $/ at the end of a string. $/ defaults to a newline.


		  
		  

		  
Tasks:
1.Define a variable with white spaces in value
2.Remove the whilespaces in the variable
3.output the result
		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. #1.Define a variable with white spaces in value

  2. s=" \t  how to trim a string  \t"

  3. echo -e "'$s'"

  4. 

  5. #2.Remove the whilespaces in the variable

  6. s2=`echo -e "$s" |sed "s/^[[:space:]]*\|[[:space:]]*$//g"`

  7. s3=`echo -e "$s" |sed -e 's/^[[:space:]]*//g' -e 's/[[:space:]]*$//g'`

  8. 

  9. #3.output the result

  10. echo -e "'$s2'"

  11. echo -e "'$s3'"

  12. 

  13. 

  14. -------output----------



  1. #1.Define a variable with white spaces in value

  2. ' 	  how to trim a string  	'

  3. 

  4. #2.Remove the whilespaces in the variable

  5. 

  6. #3.output the result

  7. 'how to trim a string'

  8. 'how to trim a string'



                
  1. #1.Define a variable with white spaces in value

  2. $_=" \t  how to trim a string  \t";

  3. print "'".$_."'\n";

  4. 

  5. #2.Remove the whilespaces in the variable

  6. s/^[[:space:]]*|[[:space:]]*$//g;

  7. 

  8. #3.output the result

  9. print "'".$_."'";

  10. 

  11. -------output----------



  1. #1.Define a variable with white spaces in value

  2. ' 	  how to trim a string  	'

  3. 

  4. #2.Remove the whilespaces in the variable

  5. 

  6. #3.output the result

  7. 'how to trim a string'



                
  1. #1.Define a variable with white spaces in value

  2. s=" \t  how to trim a string  \t"

  3. print "'%s'" %s

  4. 

  5. #2.Remove the whilespaces in the variable

  6. s2=s.strip()

  7. import re

  8. s3=re.sub(r'^\s*|\s*$',r'',s)

  9. 

  10. #3.output the result

  11. print "'%s'" % s2

  12. print "'%s'" % s3

  13. 

  14. -------output----------



  1. #1.Define a variable with white spaces in value 

  2. ' 	  how to trim a string  	'

  3. 

  4. #2.Remove the whilespaces in the variable 

  5. 

  6. #3.output the result 

  7. 'how to trim a string'

  8. 'how to trim a string'



              

             
            
 
          

          

		  

        
          

		  
String: Concatenate two strings 

		  

		  
		  

		  
Tasks:
1.Assign a string to a variable.
2.Catenate two strings and print the result.
		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. #1.Assign a string to a variable.

  2. name="Scarborough Fair"

  3. 

  4. #2.Catenate two strings and print the result.

  5. echo "hello, $name"

  6. printf "hello, %s\n" "$name"

  7. 

  8. -------output----------



  1. #1.Assign a string to a variable.

  2. 

  3. #2.Catenate two strings and print the result.

  4. hello, Scarborough Fair

  5. hello, Scarborough Fair



                
  1. #1.Assign a string to a variable.

  2. $name="Scarborough Fair";

  3. 

  4. #2.Catenate two strings and print the result.

  5. print "hello, $name\n";

  6. #  using dot operator

  7. print "hello, ".$name."\n";

  8. #  using join function

  9. print join(" ","hello",$name);

  10. printf "hello, %s\n", "$name";

  11. 

  12. -------output----------



  1. #1.Assign a string to a variable.

  2. 

  3. #2.Catenate two strings and print the result.

  4. hello, Scarborough Fair

  5. #  using dot operator

  6. hello, Scarborough Fair

  7. #  using join function

  8. hello Scarborough Fairhello, Scarborough Fair



                
  1. #1.Assign a string to a variable.

  2. name="Scarborough Fair"

  3. 

  4. #2.Catenate two strings and print the result.

  5. print "hello, "+name

  6. print "hello,", name

  7. print "hello, %s" % (name)

  8. 

  9. -------output----------



  1. #1.Assign a string to a variable. 

  2. 

  3. #2.Catenate two strings and print the result. 

  4. hello, Scarborough Fair

  5. hello, Scarborough Fair

  6. hello, Scarborough Fair



              

             
            
 
          

          

		  

        
          

		  
String: Split string into array 

		  

		  
		  

		  
Tasks:
1.Define a variable with string value
2.Get and output the array
		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. #1.Define a variable with string value

  2. str="bing.com|google.com|baidu.com|yahoo.com"

  3. 

  4. #2.Get and output the array

  5. IFS='|' sites=(`echo $str`)

  6. echo "${sites[@]}"

  7. unset IFS

  8. 

  9. -------output----------



  1. #1.Define a variable with string value

  2. 

  3. #2.Get and output the array

  4. bing.com google.com baidu.com yahoo.com



                
  1. #1.Define a variable with string value

  2. $str="bing.com|google.com|baidu.com|yahoo.com";

  3. 

  4. #2.Get and output the array

  5. @sites=split(/\|/,$str);

  6. print "@sites";

  7. 

  8. -------output----------



  1. #1.Define a variable with string value

  2. 

  3. #2.Get and output the array

  4. bing.com google.com baidu.com yahoo.com



                
  1. #1.Define a variable with string value

  2. str="bing.com|google.com|baidu.com|yahoo.com"

  3. 

  4. #2.Get and output the array

  5. sites=str.split('|')

  6. print sites

  7. 

  8. -------output----------



  1. #1.Define a variable with string value 

  2. 

  3. #2.Get and output the array 

  4. ['bing.com', 'google.com', 'baidu.com', 'yahoo.com']