17. Self-Learning Linux path: Conditional judgment statement for Bash programming

BASH Programming Conditional judgment: Determine whether the prerequisites for subsequent operations are satisfied

Common Types of Judgments:

Integer judgment:

Character Judgment:

File judgment:

$?: Status return value

0: True

1-255: Fake

We can use the status return value as the judging condition, do not need to add ' '

Boolean value:

True and False

Logical operation:

and Operation:&&

Or Operation: | |

Non-op:!

The conditions in bash are judged using if:

Single branch:

if condition; Then

Branch 1;

Fi

Dual Branch:

if condition; Then

Branch 1;

Else

Branch 2;

Fi

Multi-branch:

if condition; Then

Branch 1;

Elif Condition 2; Then

Branch 2;

elif condition 3; Then

Branch 3;

.

.

Else

Branch N;

Fi

Exercise: 1. Let the user specify a file, determine: If the file has a blank line, the number of blank lines is displayed

Nano spaceline.sh

#!/bin/bash

#

Read-p "Enter a file path:" Fliename

If grep "^$" $fileName &>/dev/null; Then do not add ' because we are not using the result of the command but the command state return value

Linescount= ' grep ' ^$ ' $fileName | Wc-l '

echo "$fileName has $linesCount space lines."

Fi

Exercise: 2. Let the user specify a file, determine: If the file has a blank line, the number of blank lines will be displayed, otherwise there will be no blank line output

CP spaceline.sh spaceline2.sh

Nano spaceline2.sh

#!/bin/bash

#

Read-p "Enter a file path:" FileName

If grep "^$" $fileName &>/dev/null; Then

Linescount= ' grep ' ^$ ' $fileName | Wc-l '

echo "$fileName has $linesCount space lines."

Else

echo "$fileName have no space lines"

Fi

17. Self-Learning Linux path: Conditional judgment statement for Bash programming