One of the good things about Mac/iOS programming is that they share most of the SDK, obviously, except the UI classes and some OS specific parts. So, when you’re creating the model and classes that don’t need user interface, you will find that most of your code will likely just work on Mac, or it will work with some minor changes. Insert the OS installation disc, if necessary. If the Mac still has a disc drive and is still running Mac OS X Snow Leopard (10.6) or below, insert the OS installation disc into your computer to ensure Apple Hardware Test can boot. Fast.com is a super-simple WiFi speed test app for Mac and other computers and devices with a modern web browser. Unlike most other similar apps, Fast.com only measures your download speed, and it does so as soon as you open it.
Condition evaluation.
Evaluate an expression and, if it evaluates to true, return a zero (true) exit status; otherwise return 1 (false). If there is no expression, test also returns 1 (false).
[ is a synonym for test but requires a final argument of ].
The double bracket [[ construct, also known as 'extended test' or 'New Test' is more versatile, the old test [ is more portable.
In most cases, on modern systems, you should prefer the use of new test [[
If one side of the expression expr evaluates to nothing (Null) then [ will throw an error, [[ will handle this automatically.
Spaces around the brackets are important - each operator and operand must be a separate argument.
To do a simple numeric comparison (or any other shell arithmetic), use(( )) instead of test:
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To test variables you should quote the 'variablename' as they may undergo word splitting or globbing, with New test [[ this is not necessary
[ '$DEMO' = 5 ]
[[ $DEMO 10 ]]
Multiple Expressions can be combined using the following operators, listed in decreasing order of precedence.
The old test [ can also use the -a and -o operators, and ( ... ) grouping, as defined by POSIX but only for strictly limited cases, and these are now marked as deprecated.
The test and [ builtins evaluate conditional expressions using a set of rules based on the number of arguments.
File type tests
These options test for particular types of files. All cases will only return True (0) if the file exists.
File Age Tests (modification date)
String tests
Comparison strings for test do not need to be quoted, though you can quote them to protect characters with special meaning to the shell, e.g. spaces.
Comparisons using New test [[ perform pattern matching against the string on the right hand side unless you quote the 'string' on the right. This prevents any characters with special meaning in pattern matching from taking effect.
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Numeric tests
These are normally used in conjunction with another non-math test operator somewhere in the expression.
For a purely numeric comparison, it is better to use (( )) instead of test or New test [[
The arguments must be entirely numeric (possibly negative), or the special expression -l STRING which evaluates to the length of STRING. The < and > operators can also be used with new test [[
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Examples
Test if the non existent file paris.txt is readable, the value returned is false (non zero)
Test if the file amsterdam.txt exists:
Test the logged in username, if the logname variable = scott then the test returns TRUE (0):
The double bracket [[ construct is a “compound command” while test and the single bracket [ are shell built-ins.
“The test of a vocation is the love of the drudgery it involves” ~ Logan Pearsall
Related macOS commands:
eval - Evaluate several commands/arguments.
expr - Evaluate expressions.
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