Common condition tests for shell
Here are some commonly used condition test tables in shells for your reference and reference
Different test types
There are three types of tests that can be done in Bash:
- Test string
- Test number
- Test file
Test string
| condition | significance |
|---|---|
| $string1 = $string2 | Whether the two strings are equal. Shell is case sensitive, so A and a are not the same. |
| $string1 != $string2 | Whether the two strings are different. |
| -z $string | Whether the string string is empty. z is the first letter of zero, which means "zero" in English. |
| -n $string | Whether string is not empty. n is the first letter of English not, which means "not" in English. |
example:
#!/bin/bash
if [ -z $1 ]
then
echo "No parameter"
else
echo "There is at least one parameter"
fi
Test string
| condition | significance |
|---|---|
| $num1 -eq $num2 | Whether the two numbers are equal. It is not the same as the symbol (=) used to determine the character string. eq is the abbreviation of equal, which means "equal" in English. |
| $ num1 -ne $ num2 | Whether the two numbers are different. ne is the abbreviation of not equal, which means "not equal" in English. |
| $num1 -lt $num2 | Whether the number num1 is less than num2. lt is the abbreviation of lower than, which means "less than" in English. |
| $ num1 -le $ num2 | Whether the number num1 is less than or equal to num2. le is the abbreviation of lower or equal, which means "less than or equal to" in English. |
| $num1 -gt $num2 | Whether the number num1 is greater than num2. gt is the abbreviation of greater than, which means "greater than" in English. |
| $num1 -ge $num2 | Whether the number num1 is greater than or equal to num2. Ge is the abbreviation of greater or equal, which means "greater than or equal" in English. |
example:
#!/bin/bash
if [ $1 -ge 10 ]
then
echo "You have entered a number greater than 10 or equal to 10"
else
echo "You have entered a number lower than 10"
fi
Test file
| condition | significance |
|---|---|
| -e $ file | Whether the file exists. e is the first letter of exist, which means "exist". |
| -d $file | Whether the file is a directory. Because everything in Linux is a file, a directory is also a kind of file. d is the first letter of directory, which means "directory". |
| -f $file | Whether the file is a file. f is the first letter of file, which means "file". |
| -L $file | Whether the file is a symbolic link file. L is the first letter of link, which means "link". |
| -r $file | Whether the file is readable. r is the first letter of readable, which means "readable". |
| -w $file | Whether the file is writable. w is the first letter of writable, which means "writable". |
| -x $file | Whether the file is executable. x is the first letter of executable, which means "executable". |
| $ file1 -nt $ file2 | Whether file file1 is newer than file2. nt is the abbreviation of newer than, which means "newer". |
| $ file1 -from $ file2 | Whether file file1 is older than file2. ot is the abbreviation of older than, which means "older". |
example:
#!/bin/bash
read -p 'Enter a directory : ' file
if [ -d $file ]
then
echo "$file is a directory"
else
echo "$file is not a directory"
fi
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Reference: Linux Command Line and Shell Script Programming Encyclopedia/43 When the condition comes out, Shell is not satisfied