610 Functions

   611 ---------

   612 

   613 When a group of commands are repeatedly being used within a script, it is convenient to group them as a function. This saves a lot of time and you can avoid retyping the code again and again. Also, it will help you maintain your code easily. Let's see how we can define a simple function, ``hello-world``. Functions can be defined in bash, either using the ``function`` built-in followed by the function name or just the function name followed by a pair of parentheses. 

   614 ::

   615 

   616   function hello-world

   617   { 

   618   echo "Hello, World."; 

   619   }

   620 

   621   hello-world () {

   622     echo "Hello, World.";

   623   }

   624 

   625   $ hello-world

   626   Hello, World.

   627 

   628 Passing parameters to functions is similar to passing them to scripts. 

   629 ::

   630 

   631   function hello-name

   632   { 

   633   echo "Hello, $1."; 

   634   }

   635 

   636   $ hello-name 9

   637   Hello, 9.

   638 

   639 Any variables that you define within a function, will be added to the global namespace. If you wish to define variables that are restricted to the scope of the function, define a variable using the ``local`` built-in command of bash.

   640 

   641 We shall now write a function for the word frequency generating script that we had looked at in the previous session. 

   642 

   643 ::

   644 

   645   function word_frequency {

   646     if [ $# -ne 1 ]

   647     then

   648       echo "Usage: $0 file_name"

   649       exit 1

   650     else 

   651       if [ -f "$1" ]

   652       then

   653         grep  "[A-Za-z]*" -o "$1" | tr 'A-Z' 'a-z' | sort | uniq -c | sort -nr | less

   654       fi

   655     fi

   656   }

   657 

   658 As an exercise, modify the function to accept the input for the number of top frequency words to be shown (if none is given, assume 10).

   659