C2110 UNIX and programming Lesson 8 -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
Lesson 8
PS / 2020 Distance form of teaching: Rev2
C2110 UNIX and programming Lesson 8 -2Summary
L7
➢ Bash
C2110 UNIX and programming Lesson 8 -3Decision
Block
Yes
No
?
Yes
No
block 1
block 2
state?
Yes
No
block 1
change
initialization
Conditional block execution (conditions) Cyclic block execution (loops)
Typical use of decision block
counter (variable)
C2110 UNIX and programming Lesson 8 -4-
Conditions
if command1; then
command2
...
else
command3
...
fi
if ! mkdir directory 2> /dev/null; then
echo “I cannot create directory!"
exit 1
fi
Boolean expressions:
[[ number1 operator number2 ]]
[[ operator string1 ]]
More complex logical expressions:
|| logical or
&& logical and
! negation
It is possible to test the return
value of a command or the
result of a logical expression.
Example:
[[ (I -ge 5) && (I -le 10) ]]
C2110 UNIX and programming Lesson 8 -5Loop
using while
I < N
Yes
No
I = I + 1
N = 10
I= 0
writestr
"X"
counter (variable)
N=10
I=0
while [[ I –lt N ]]; do
echo "X"
((I = I + 1))
done
While loop is used mainly in situations where
changing the "counter" is a complex matter or
cannot be controlled by a quantifiable counter (it
depends, for example, on the result of a command).
while command1; do
command2
...
done
C2110 UNIX and programming Lesson 8 -6Next
Subject
➢ Bash
C2110 UNIX and programming Lesson 8 -7-
Content
➢ Loop
• for vs while
➢ Troubleshooting
• syntactic and logical errors, syntax highlighting, static
analysis, debugging
➢ Functions
➢ Lollipop Competition