Automating frequent tasks

Different kinds of test

In general, tests are carried out either by enclosing them in square braces (as above) or by using the command test(C). The most useful tests are as follows:

-r file: True if a file called file exists and is readable.
-w file: True if a file called file exists and is writable.
-x file: True if a file called file exists and is executable.
-s file: True is a file called file exists and is not empty.
-d file: True if a file called file exists and is a directory.
-f file: True if a file called file exists and is a regular file.
-z string: True if the length of string is zero.
-n string: True if the length of string is non-zero.
string1 = string2: True if string1 equals string2.
string1 != string2: True if string1 is not equal to string2.
number1 -eq number2: True if the integer number1 equals number2.
number1 -ne number2: True if the integer number1 is not equal to number2.
number1 -gt number2: True if the integer number1 is greater than number2.
number1 -lt number2: True if the integer number1 is less than number2.
number1 -ge number2: True if the integer number1 is greater than or equal to number2.
number1 -le number2: True if the integer number1 is less than or equal to number2.

In addition to these tests, there are a number of others; see test(C) for details. In general, the tests listed here should be sufficient to let you test for the existence of files, to check whether your script has permission to manipulate a given file, to compare two numbers, and to see if a string matches some value. These are the commonest comparisons used to help a script decide on a course of action to take.