The basic implementation of testing and judging shell scripts

condition test: Whether the condition of judgment is established

1. type of condition test: file test; integer comparison; string comparison; logic test

2 . Conditional test Syntax:[ operator conditional expression ] equals test operator conditional expression

3. file test:

1) Type of file:-(normal file),D(inside), c(character device),s(socket), b(block device),p(pipe file, Can be used for screen demonstrations)

2) file judge:-F file,-D Directory,e- file exists,-rwx to determine whether there is permission [ operator file /c13>]

4. integer comparison

1) syntax:[ number 1 operator number 2]

2) Operator:-eq ,-ne unequal,-gt greater than,-lt less than,-ge greater than equals,-le less than equals

5. String comparison

1) syntax:[ string 1 operator string 2]

2) Operator: = = equal ,-Z is empty,! = Unequal

Second, if use:

1. Single-branch syntax:

If [ conditional expression ];Then

Command actions

Fi

Note: When the condition is established, the command operation is executed, and the exit does not execute when the command is not

2. Double-branch syntax:

If [ conditional expression ];Then

Command operation for condition-established execution

Else

The condition does not establish the action performed

Fi

Note: A two-branch operation is done on both sides of the condition,

3. If Multi-branch syntax:

If [ conditional expression 1];Then

Command Action 1

elif [ conditional expression 2];Then

Command Action 2

elif [ conditional expression 2];Then

Command Action 3

Else

default command Action

Fi

Note: Multiple branches perform multiple test conditions, and only command operations that have a condition set are performed.

Practice cases:

Case:
Str1=hehe
[$STR 1 = = hehe]
[$LANG = = en]
[$STR 1! = linuxfan.cn]
str2= # #直接回车
[-Z $STR 2]
4) Logical Judgment
Logical judgment is the same as or not.
Grammar:
[Expression 1] && (and), | | (OR),! (non) [expression 2]
Command 1 &&,| |,! Command 2
Case:
Compile and install:
./configure &&make &&make
[1–ge 2] | | [1–lt 2] # #测试结果为真
[$LANG! = en]

2.if judgment
1) Single Branch
Grammar:
if [Condition];then
Command
Fi
Case: Determine if the LFTP is installed if not installed
VI install_lftp.sh
#!/bin/bash
Rpm-qa |grep lftp 1>/dev/null
If [$?-ne 0];then
Yum-y Install lftp &>/dev/null &&echo "lftp installed."
Fi
2) if dual branch
Grammar:
if [Condition];then
Command 1
Else
Command 2
Fi
Use a two-branch single-branch case script to overwrite if the installation is already installed and is installed if it is not installed.
3) If multi-branch
Grammar:
if [Condition 1];then
Command 1
elif [Condition 2];then
Command 2
....
Else
Command
Fi
Case:
#!/bin/bash
Ls/etc/rc.d/rc3.d/s60vsftpd
If [$?-ne 0]
Then
Chkconfig vsftpd on
elif [-X/ETC/INIT.D/VSFTPD]
Then
chmod +x/etc/init.d/vsftpd
Else
/ETC/INIT.D/VSFTPD restart
Fi
Comprehensive case:
[email protected] bin]# cat if_then_fi.sh
#!/bin/bash

name=$ (basename)

If [$#-ne 2-a $#-ne 3];then
echo "Usage: $name vaule1 value2"
echo "$name value1 value2 vaule3"
Exit 1
Fi

If [$#-eq 2];then
echo "Args:$1,$2"
Else
echo "Three args:$1,$2,$3"
Fi

If [$#-eq 2];then
If [$1-gt $];then
echo "$ > $"
elif [$1-lt $];then
echo "$ < $"
Else
echo "$ = $"
Fi
Else
If [$1-ge $2-a $1-ge $];then
echo "$ >=$2,$1 >=$3"
elif [$1-ge $2-a $1-le $];then
echo "$ >=$2,$1 <="
elif [$1-lt $2-a $1-ge $];then
echo "$ < $2,$1 >="
Else
echo "$ < $2,$1 < $"
Fi
Fi
Exit 0
[Email protected] bin]#

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The basic implementation of testing and judging shell scripts