Scripting languages course 2
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Scripting Languages Course 2. Diana Trandabăț. Master in Computational Linguistics - 1 st year 2013-2014. Today’s lecture.

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Scripting Languages Course 2

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Scripting languages course 2

Scripting LanguagesCourse 2

Diana Trandabăț

Master in Computational Linguistics - 1st year

2013-2014


Today s lecture

Today’s lecture

  • Visit http://www.isi.edu/natural-language/mt/unix.txt and follow the tutorial to learn how to obtain the frequency of each word in a text, the frequency of bigrams and trigrams.


Other useful commands

Other useful commands

  • Transform uppercase characters into lower case:

    tr ’[:upper:]’ ’[:lower:]’ < INFILE

  • This command is not needed before sort, since sort can ignore the difference between upper and lower case characters:

    sort –f filename

  • Sort with the second field as key field

    sort +1 –nr freq_list

  • Working with references. Read the explanations on the egrep guide (page 29)

    sed -n ’s/.*(\(.*\)).*/\1/p’ sonnets.txt


File management with shell commands

File Management with Shell Commands

  • Options can be combined

    • a verbose listing of files by last modification date:

      ls -lt


File management with shell commands1

File Management with Shell Commands

The verbose listing shows the file permissions of a given file:

-rwxr-xr-x

  • directories have a "d" in the first column

  • regular files have a "-".

  • the remaining 9 characters indicate owner, group, and world permissions of the file

  • An "r" indicates it's readable

  • "w" is writable,

  • "x" is executable

    A dash in the column instead of a letter means that particular permission is turned off.


File management with shell commands2

File Management with Shell Commands

r readable

w writable

x executable

- permission is turned off

-rwxr-xr-x

a plain file that is read-write-execute by the owner, and read-execute by group and world.

drwx------

a directory that is read-write-execute by owner, and group and world have no permissions at all.


File management with shell commands3

File Management with Shell Commands

chmod[permissions] [file]

Changes the permissions of the named file.

You can use numbers:

chmod 755 index.html

The first number translates to permissions by the owner. The second is permissions for the group.

The third is permissions for everyone.

Number Perms

0 --- no permissions

1 --x executable only

2 -w- writable only

3 -wx writable and executable

4 r--- readable only

5 r-x readable and executable

6 rw- readable and writable

7 rwx readable, writable, and executable


File management with shell commands4

File Management with Shell Commands

A second way of setting permissions is with letters:

chmod u+rwx index.html

chmod go+rx index.html

u is the owner's ("user's") permissions

g is the group permissions

o is "other" or world permissions.

The + sign turns the stated permissions on;

the — sign turns them off

If you want to change a file so that it's group writable, but not readable or executable, you'd do:

% chmod g+w,g-rx index.html


Example of a simple shell script

Example of a simple shell script

# This script displays the date, time,

# username and current directory.

echo "Date and time is:"

date

echo "Your username is: `whoami`"

echo "Your current directory is:"

pwd


Example of a simple shell script1

Example of a simple shell script

# This script displays the date, time,

# username and current directory.

lines beginning with a hash (#) are comments and are not interpreted by the Shell.


Example of a simple shell script2

Example of a simple shell script

# This script displays the date, time,

# username and current directory.

echo "Date and time is:"

  • When used as a Shell command echo echo prints its argument

  • When echoing multiple words, they must be placed within quotes (single or double)


Example of a simple shell script3

Example of a simple shell script

# This script displays the date, time,

# username and current directory.

echo "Date and time is:"

date

echo "Your username is: `whoami`"

The backquotes (`) around the command whoami illustrate the use of COMMAND SUBSTITUTION: To include the output from one command within the command line for another command, enclose the command whose output is to be included within `backquotes`.


Executing the shell script

Executing the shell script

  • Before using a file as a shell script you must change its access permissions so that you have execute permission on the file, otherwise the error message Permission denied is displayed.

  • To give yourself execute permission for the file containing the script use the command:

    chmod u+rwx display


Executing the shell script1

Executing the shell script

chmodu-x display

  • To run the shell script, type its name at the prompt preceded by “sh” or “./”.

  • The commands in the script will then execute one at a time as though you were typing them in at the terminal.

    sh display.sh

    ./ display.sh


More examples of pipelines

More examples of pipelines

  • See the egrep guide, pages 31-37.

  • Some of them are already covered by the Unix for computational linguists guide.

  • Create a script file for each exercise (i.e. for bigrams, trigrams etc.)


Scripting languages course 2

Great!

See you next time!


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