Note: Each end of square brackets must be blank.
#!/bin/bash
if [ condition1 ]; then
echo "condition 1"
elif [ condition2 ]; then
echo "condition 2"
else
echo "else"
fi
There are many different ways that an conditional statement can be used. These are summarized here:
| String Comparison |
Description |
| Str1 = Str2 |
Returns true if the strings are equal |
| Str1 != Str2 |
Returns true if the strings are not equal |
| -n Str1 |
Returns true if the string is not null |
| -z Str1 |
Returns true if the string is null |
| Numeric Comparison |
Description |
| expr1 -eq expr2 |
Returns true if the expressions are equal |
| expr1 -ne expr2 |
Returns true if the expressions are not equal |
| expr1 -gt expr2 |
Returns true if expr1 is greater than expr2 |
| expr1 -ge expr2 |
Returns true if expr1 is greater than or equal to expr2 |
| expr1 -lt expr2 |
Returns true if expr1 is less than expr2 |
| expr1 -le expr2 |
Returns true if expr1 is less than or equal to expr2 |
| ! expr1 |
Negates the result of the expression |
| File Conditionals |
Description |
| -d file |
True if the file is a directory |
| -e file |
True if the file exists (note that this is not particularly portable, thus -f is generally used) |
| -f file |
True if the provided string is a file |
| -g file |
True if the group id is set on a file |
| -r file |
True if the file is readable |
| -s file |
True if the file has a non-zero size |
| -u |
True if the user id is set on a file |
| -w |
True if the file is writable |
| -x |
True if the file is an executable |