C2110 UNIX and programming Lesson 8 / Module 3 -1C2110
UNIX and programming
Petr Kulhanek
kulhanek@chemi.muni.cz
National Center for Biomolecular Research, Faculty of Science
Masaryk University, Kamenice 5, CZ-62500 Brno
PS / 2020 Distance form of teaching: Rev1
8. lesson / module 3
C2110 UNIX and programming Lesson 8 / Module 3 -2-
Functions
C2110 UNIX and programming Lesson 8 / Module 3 -3Functions
- Definition
Function is a construct that allows you to group a piece of code so that it can be easily
used in multiple places in a script. The function therefore simplifies and notation of
repetitive tasks.
Definition:
function name () {
command1
command2
...
}
function name {
command1
command2
...
}
name () {
command1
command2
...
}
alternative notations
Function arguments are not declared, so there is no control in the number of arguments,
type control, function can not be overloaded. The specified arguments are available via
special variables #, 1 to 9, *. Functions are called as an existing command. Variables in the
function are global (can be changed using keyword local). Documentation: man bash,
section FUNCTIONS.
C2110 UNIX and programming Lesson 8 / Module 3 -4Functions
- Usage
# print line – the length is in the first argument
function print_line () {
N=$1
for((J=1;J <= N;J++)); do
echo –n " X"
done
echo ""
}
# use function
print_line 10 # print line 10 characters long
print_line 5 # print line 5 characters long
value of argument is available in a special variable 1
C2110 UNIX and programming Lesson 8 / Module 3 -5-
Exercises
1. Write one script that prints a square and a triangle (similar to Tasks 1 and 2) for one
specified length one after another to the terminal. In the script, identify the part that is
being repeated and rewrite it using function.
X X X X
X X X X
X X X X
X X X X
X X X X
X X X
X X
X
Ignore the fact that it is not visually a square.
However, number of X characters for a line and
the number of lines must be the same. Possibly
use "X " - X and a space.