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

Topics about path

Path: get the dirname of a full path 


		  
		  

		  
Tasks:
1.1. define a variable with value of a file's full path
2.2. print the directory of the file
		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. #1.1. define a variable with value of a file's full path

  2. myfile="/home/remote/5th Jun/bash perl python.txt"

  3. 

  4. #2.2. print the directory of the file

  5. echo "`dirname "$myfile"`"

  6. #  another way

  7. echo "${myfile%/*}"

  8. #  the 3rd way, use regular expression

  9. sed "s/\(.*\)\/.*/\1/" <<<"$myfile"

  10. 

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



  1. #1.1. define a variable with value of a file's full path

  2. 

  3. #2.2. print the directory of the file

  4. /home/remote/5th Jun

  5. #  another way

  6. /home/remote/5th Jun

  7. #  the 3rd way, use regular expression

  8. /home/remote/5th Jun



                
  1. use feature ":5.10" ;

  2. use Cwd qw(abs_path cwd);

  3. use File::Basename;

  4. #1.1. define a variable with value of a file's full path

  5. $mypath="/home/remote/5th Jun/bash perl python.txt";

  6. 

  7. #2.2. print the directory of the file

  8. print dirname($mypath)."\n";

  9. #  another way, use regex

  10. $mypath =~ s/(.*)\/.*/\1/;

  11. print $mypath;

  12. 

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



  1. #1.1. define a variable with value of a file's full path

  2. 

  3. #2.2. print the directory of the file

  4. /home/remote/5th Jun

  5. #  another way, use regex

  6. /home/remote/5th Jun



                
  1. import os

  2. #1.1. define a variable with value of a file's full path

  3. mypath="/home/remote/5th Jun/bash perl python.txt"

  4. 

  5. #2.2. print the directory of the file

  6. print os.path.dirname(os.path.abspath(mypath))

  7. #  or use os.path.split

  8. dname, fname = os.path.split(mypath)

  9. print dname

  10. #  or use regex

  11. import re

  12. print re.sub(r'(.*)\/.*', r'\1', mypath, flags=re.M)

  13. 

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



  1. #1.1. define a variable with value of a file's full path 

  2. 

  3. #2.2. print the directory of the file 

  4. /home/remote/5th Jun

  5. #  or use os.path.split 

  6. /home/remote/5th Jun

  7. #  or use regex 

  8. /home/remote/5th Jun



              

             
            
 
          

          

		  

        
          

		  
Path: get the basename of a full path 

		  

		  
		  

		  
Tasks:
1.1. define a variable with value of a file's full path
2.2. print the filename of the file
		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. #1.1. define a variable with value of a file's full path

  2. myfile="/home/remote/5th Jun/bash perl python.txt"

  3. 

  4. #2.2. print the filename of the file

  5. echo "`basename "$myfile"`"

  6. echo "`basename "$myfile" ".txt"`"

  7. #  or

  8. echo "${myfile##*/}"

  9. #  or use awk

  10. awk -F/ '{print $NF}' <<<"$myfile"

  11. #  or use sed

  12. sed "s/.*\///" <<<"$myfile"

  13. sed "s/.*\/\(.*\)/\1/" <<<"$myfile"

  14. #  or use rev and cut

  15. rev <<<"$myfile" |cut -d"/" -f 1 |rev

  16. 

  17. -------output----------



  1. #1.1. define a variable with value of a file's full path

  2. 

  3. #2.2. print the filename of the file

  4. bash perl python.txt

  5. bash perl python

  6. #  or

  7. bash perl python.txt

  8. #  or use awk

  9. bash perl python.txt

  10. #  or use sed

  11. bash perl python.txt

  12. bash perl python.txt

  13. #  or use rev and cut

  14. bash perl python.txt



                
  1. use feature ":5.10" ;

  2. use Cwd qw(abs_path cwd);

  3. use File::Basename;

  4. #1.1. define a variable with value of a file's full path

  5. $mypath="/home/remote/5th Jun/bash perl python.txt";

  6. 

  7. #2.2. print the filename of the file

  8. print basename($mypath);

  9. 

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



  1. #1.1. define a variable with value of a file's full path

  2. 

  3. #2.2. print the filename of the file

  4. bash perl python.txt



                
  1. import os

  2. mypath="/home/remote/5th Jun/bash perl python.txt"

  3. #1.1. define a variable with value of a file's full path

  4. dname, fname = os.path.split(mypath)

  5. print fname

  6. 

  7. #2.2. print the filename of the file

  8. print os.path.basename(mypath)

  9. 

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



  1. #1.1. define a variable with value of a file's full path 

  2. bash perl python.txt

  3. 

  4. #2.2. print the filename of the file 

  5. bash perl python.txt



              

             
            
 
          

          

		  

        
          

		  
Path: get the path of current script 

		  
1. create the script file.
2. run the script file to get it's path

		  
		  

		  
Tasks:

		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. # 1.

  2. cat >/tmp/test.sh<<"EOD"

  3. # the perfect way

  4. (cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd)

  5. # wrong if you use: source scriptname [arguments]

  6. (cd "$( dirname "$0" )" && pwd)

  7. EOD

  8. 

  9. # 2.

  10. bash /tmp/test.sh

  11. source /tmp/test.sh 2>&1

  12. 

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



  1. # 1.

  2. 

  3. # 2.

  4. # the perfect way

  5. /tmp

  6. # wrong if you use: source scriptname [arguments]

  7. /tmp

  8. # the perfect way

  9. /tmp

  10. # wrong if you use: source scriptname [arguments]

  11. /home/neutrino0717/bash4u



                
  1. # 1.

  2. cat >/tmp/test.pl<<"EOF"

  3. use Cwd 'abs_path';

  4. print abs_path($0);

  5. EOF

  6. 

  7. #  2.

  8. perl /tmp/test.pl

  9. 

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



  1. /tmp/test.pl



                
  1. # 1.

  2. cat >/tmp/test.py<<"EOF"

  3. import os

  4. print os.path.dirname(os.path.realpath(__file__))

  5. print os.path.dirname(os.path.abspath(__file__))

  6. EOF

  7. 

  8. # 2.

  9. python /tmp/test.py

  10. 

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



  1. /tmp

  2. /tmp



              

             
            
 
          

          

		  

        
          

		  
Path: get the current working dir 

		  
In bash:
A good practice is to use subshell,and thus will not affect the working directory of parent shell.
alias new_job='(cd /boot; pwd; echo "in subshell: $$ $BASHPID. working dir: `pwd`")'

		  
		  

		  
Tasks:

		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. echo `pwd`

  2. 

  3. -------output----------



  1. /home/neutrino0717/bash4u



                
  1. #get the currnet working directory

  2. use Cwd;

  3. print getcwd();

  4. 

  5. -------output----------



  1. #get the currnet working directory

  2. /home/neutrino0717/bash4u



                
  1. import os

  2. print os.getcwd()

  3. 

  4. -------output----------



  1. /home/neutrino0717/bash4u



              

             
            
 
          

          

		  

        
          

		  
Path: how to change working dir 

		  
In bash:
If you are running bash v4 or better, the PID of the subshell is available in $BASHPID.

In python:
The best way is to use File::chdir and $CWD variable
Using below maybe problematic in case of exeptions:
  my $cwd_orig = cwd;
  chdir "$cwd_new";
  #do some work...
  chdir $cwd_origin;

		  
		  

		  
Tasks:

		  

		       
          
          

             
             

		     

                Bash
                Perl
                Python			   
		     

             
              

                
  1. #start subshell

  2. cd /bin

  3. echo "In parshell: $$ $BASHPID. working dir: `pwd`"

  4. (cd /home; echo "in subshell: $$ $BASHPID. working dir: `pwd`")

  5. echo "In parshell: $$ $BASHPID. working dir: `pwd`"

  6. 

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



  1. #start subshell

  2. In parshell: 18964 18964. working dir: /bin

  3. in subshell: 18964 18966. working dir: /home

  4. In parshell: 18964 18964. working dir: /bin



                
  1. # 

  2. use Cwd;

  3. use File::chdir;

  4. chdir "/media";

  5. print "in main, working dir: ".getcwd()."\n";

  6. $CWD = '/bin';

  7. print "in main, working dir: ".getcwd()."\n";

  8. {

  9. local $CWD = "/home";

  10. print "in {}, working dir: ".getcwd()."\n";

  11. }

  12. print "back to main, working dir: ".getcwd()."\n";

  13. 

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



  1. # 

  2. in main, working dir: /media

  3. in main, working dir: /bin

  4. in {}, working dir: /home

  5. back to main, working dir: /bin



                
  1. #todo

  2. 

  3. -------output----------



  1. #todo