1: Conditional judgment syntax format
Format 1: test conditional expression
Format 2: [conditional expression ]
Format 3: [[conditional expression ]] Support regular=
Note: check the conditional judgment of the test expression through man test
2: Judge the file type (the following are common)
- e Determine whether the file exists
- f Determine whether the file exists and is an ordinary file
- d Determine whether the file exists and is a directory
- L Determine whether the file exists and is a soft connection
- b Determine whether the file exists and is a device file
- S Determine whether the file exists and is a socket file
- c Determine whether the file exists and is a character device file
- p Determine whether the file exists and is a named pipe file
- s Judge whether the file exists and is a non empty file (with content)
2: Judge file permissions (the following are common)
- r Is the current user readable
- w Is it writable by the current user
- x Is the current user executable
- u Is there a suid Advanced rights adventure bit
- g sgid advanced permission enforcement bit
- k Is there a t-bit advanced permission sticky bit to control deletion
3: Judge whether the document is old or new
file1 -nt file2 Compare whether file1 is newer than File2
file1 -ot file2 Compare whether file1 is older than File2
file1 -ef file2 Compare whether it is the same file or whether the hard connection points to the same inode node
4: Judgment integer
- eq equal
- ne Unequal
- gt greater than
- lt less than
- ge Greater than or equal to
- le Less than or equal to
5: Interpretation string
- z Judge whether it is an empty string. If the string length is 0, it is true
- n Judge whether it is a non empty string. If the string length is not 0, it is true
str1 = str2 Determine whether the strings are equal
str1 != str2 Judge whether the strings are unequal
6: Multiple panduan
- a and&& Both logic and
Use - A [ 1 -eq 1 -a 1 -ne 0 ]
Use & & [1 - EQ 1] & & [1 - Ne 0]
Comprehensive actual combat:
Example 1:1: preach a test04 file directory in the / home/shell file directory,
2: Create test1.txt and test2.txt files in the test04 directory and save them in the two files
3: Write I am test1.txt and I am test2.txt
4: Create test04.sh in the / home/shell directory
5: The script is as follows:
5.1: whether the output test04 file exists,
5.2: output test04 The file exists and is a directory
5.3: judge whether test04/test1.txt exists
5.4: judge whether test04/test2.txt has content
5.5: does the current user have permission to execute test04.sh
5.6: compare text1.txt and test2.txt
5.6: define two variables str1="hellworld" and str2="hellowold"
Determine whether str1 and str2 are equal
The above script is as follows:
#!/bin/env bash # Author: lvdqiang # Desc: test file judgment # Using: execute the command 1: chmod +x /home/shell/test04.sh # Execute command 2: / home/shell/test04.sh # Determine whether the file exists echo "-----------judge test04 Does the file exist----------" test -e /home/shell/test04 A=$(echo $?) if [ $A -eq 0 ] then echo "existence" else echo "non-existent" fi echo "-----------judge test04 Does it exist and is a directory----------" test -d /home/shell/test04 B=$(echo $?) if [ $B -eq 0 ] then echo "It's a directory" else echo "Not a directory" fi echo "-----------judge test04/test1.txt Does it exist----------" test -f /home/shell/test04/test1.txt C=$(echo $?) if [ $C -eq 0 ] then echo "Is there" else echo "non-existent" fi echo "-----------judge test04/test1.txt Is there any content----------" test -s /home/shell/test04/test1.txt C=$(echo $?) if [ $C -eq 0 ] then echo "Is there" else echo "non-existent" fi echo "-----------judge test04/test2.txt Is there any content----------" test -s /home/shell/test04/test2.txt C=$(echo $?) if [ $C -eq 0 ] then echo "Is there" else echo "non-existent" fi echo "-----------judge test04.sh Do you have execution permission----------" test -x /home/shell/test04.sh C=$(echo $?) if [ $C -eq 0 ] then echo "Is there" else echo "non-existent" fi echo "-----------judge test1.txt Is it better than test2.txt new----------" test /home/shell/test04/test1.txt -nt /home/shell/test04/test2.txt C=$(echo $?) if [ $C -eq 0 ] then echo "new" else echo "Not new" fi str1="hellworld" str2="helloworld" echo "-----------str1="hellworld" and str2="hellowold" judge str1 and str2 Are they equal----------" test str1 = str2 C=$(echo $?) if [ $C -eq 0 ] then echo "equal" else echo "Unequal" fi
The above implementation results are shown in the figure below:
