Zsh path recursive relationship

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grep -r pattern dir — search recursively for pattern in dir .. 10, SEQ, query SEQuence on the same strand as the reference . Use as the full output path and do not mafiathegame.info suffix. (in most Linux distributions it's a link to /bin/ash) zsh = the Z shell (it's what it's manual page tells about it. Understanding Scope, Recursion, Return Codes, and Data Sharing. Now that you have a basic understanding of the use and operation of. In zsh, is there a way to navigate through the history of directories that I Eventually I would find /some/path/ for the cp source directory, and then type . linear recurrence relation for square of sequence given recursively.

Global Variables The following script illustrates the behavior of global variables: Then the script executes pearFunc. The output is In pearFunc: A common use for global variables is to communicate information from a function to the main script, as illustrated in the following script: The script then accesses the password using the variable PASS.

The readPass function is quite simple. It function starts by undefining PASS. Terminal echo is deactivated because you don't want someone other than the user to inadvertently see the password. Next, you read the password and store its value in PASS by using the read command.

Finally, you restore terminal echo using the stty echo command and echo a new line. Local Variables Local variables are defined using typeset command: The values are optional as the following example illustrates: The following script illustrates the behavior of local variables: Recursion In the previous section, you learned about the concept of function chaining, where one function calls another function.

Recursion is a special instance of function chaining in which a function calls itself. The following example illustrates the use of recursion: The reverse function is really simple; it determines whether there are any arguments. If there are no arguments, the function does nothing.

Otherwise, it saves the first argument, removes it from the argument list using shift and calls itself. Once this call returns, the function just prints the argument it saved. If you name the script reverse.

This will not work on Solaris and SunOS systems. The execution of this script proceeds as follows: Divide and Conquer Recursion is normally used to solve problems using a technique known as divide and conquer. Basically, divide and conquer means that a problem is divided into smaller and smaller instances until an instance that is small enough to solve directly is found. Each instance that is too big to solve directly is solved recursively, and the solutions are combined to produce a solution to the original problem.

Return Codes When a shell script completes, it can use the exit command to return exit status via an exit code. The function analogue to exit is the return command. This command allows function to return exit status. The exit status from a function is called its return code. The convention for return codes is the same as for exit codes; a 0 equals success and a nonzero equals failure. The syntax of the return command is return rc Here rc is the return code.

The following function illustrates the use of return: In this section, you will look at an example in which three functions work together and share data. Understanding Stacks For those readers who are not familiar with the programming concept of a stack, you can think of it as a stack of plates: You can access only the top plate, not any of the middle plates in the stack.

A stack in programming terms is similar. You can add or remove an item only at the top of the stack. These commands are not available in Bourne shell or ksh. Newer versions of bash and zsh have introduced these commands. In this section, you will implement each of these commands as shell functions so that they can be used with any Bourne-like shell. This allows you to handle almost any directory name.

You can get a complete list with: Disabling builtins is definitely the most useful of the four possibilities for disable. External commands have to be manipulated differently. The types given above are handled internally by the shell, so all it needs to do is remember what code to call. With external commands, the issue instead is how to find them.

I mentioned rehash above, but didn't tell you that the hash command, which you've already seen with the -d option, can be used to tell the shell how to find an external command: This is rather like an alias most people would probably do this with an alias, in fact although a little faster, though you're unlikely to notice the difference.

You can remove this with unhash. In the midst of all this, it's useful to be able to find out what the shell thinks a particular command name does. I'll just stick to whence. Its standard output isn't actually sparklingly interesting. If it's a command somehow known to the shell internally, it gets echoed back, with the alias expanded if it was an alias; if it's an external command it's printed with the full path, showing where it came from; and if it's not known the command returns status 1 and prints nothing.

A very useful option is -m, which takes any arguments as patterns using the usual zsh pattern format, in other words the same one used for matching files. If this seems a rather subtle distinction, think about what would happen if you ran Oops. Better not try this at home. Even better, don't do it at work either. There are a couple of other tricks worth mentioning: Also, the option -a searches for all commands; in the same example, this would show you both the ls command and the ls function, whereas whence would normally only show the function because that's the one that would be run.

The -a option also shows if it finds more than one external command in your path. Finally, the option -w is useful because it identifies the type of a command with a single word: Most of those are obvious, with command being an ordinary external command; hashed is an external command which has been explicitly given a path with the hash builtin, and none means it wasn't recognised as a command at all.

Now you know how we extracted the reserved words above. A close relative of whence is functions, which applies, of course, to shell functions; it usually lists the definitions of all functions given as arguments, but its relatives of which autoload is one perform various other tricks, to be described in the section on shell functions below. Parameter control There are various builtins for controlling the shells parameters. You already know how to set and use parameters, but it's a good deal more complicated than that when you look at the details.

Its easiest usage is to declare a parameter; you just give it a list of parameter names, which are created as scalar parameters. The following makes this more concrete. Then we call fn. However, the typeset next does that; as you see, we can assign to the parameter during the typeset.

Then subfn is called, which prints out the same value as in fn, because we haven't changed it this is where C or FORTRAN would differ, and wouldn't recognise the variable because it hadn't been declared in that function.

Note the value changes twice: Although you can do assignments in a typeset statement, you can't assign to arrays I already said this in the last chapter: However, the shell doesn't complain if you try to assign an array to a scalar, or vice versa; it just silently converts the type: There are other catches associated with the fact that typeset and its relatives are just ordinary commands with ordinary sets of arguments.

The answer is that backquote substitution, to be discussed below, splits words when not quoted. They are integer types, floating point types, and associative array types. They are used for arithmetic, which the shell can do as follows: The expression inside can be pretty much anything you might be used to from arithmetic in other programming languages. However, typeset allows you to specify another base for printing out.

You can use this base notation for inputting numbers, too: Floating point variables are very similar. The only difference between the two is, again, on output; -F uses a fixed point notation, while -E uses scientific mnemonic: Floating point expressions also work the way you are probably used to: The e assignment was actually an integer division, because neither 32 nor 3 is a floating point number, which must contain a dot.

That means an integer division was done, producing 10, which was then converted to a floating point number only at the end.

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Again, this is just how grown-up languages work, so it's no use cursing. The f assignment was a full floating point performance. Floating point parameters weren't available before version 3. Although this is really a matter for a later chapter, there is a library of floating point functions you can load actually it's just a way of linking in the system mathematical library. Like all other parameters created with typeset or one of its cousins, integer and floating point parameters are local to functions.

You may wonder how to create a global parameter i. There's a recent addition to the shell in version 3. The g stands for global, obviously, although it's not quite that simple: The error message, fn: This is a little confusing which is a roundabout way of saying it confused mebut consistent with how zsh usually treats parameters.

Actually, to a certain extent you don't need to use the integer and floating point parameters. Any time zsh needs a numeric expression it will force a scalar to the right value, and any time it produces a numeric expression and assigns it to a scalar, it will convert the result to a string.

This can be useful if you have a parameter which is sometimes a number, sometimes a string, since zsh does all the conversion work for you.

However, it can also be confusing if you always want a number, because zsh can't guess that for you; plus it's a little more efficient not to have to convert back and forth; plus you lose accuracy when you do, because if the number is stored as a string rather than in the internal numeric representation, what you say is what you get although zsh tends to give you quite a lot of decimal places when converting implicitly to strings.

Anyway, I'd recommend that if you know a parameter has to be an integer or floating point value you should declare it as such. If you do, remember that unlike BASIC each mathematical expression should appear as one argument in quotes. All right, what it does is hash things. These have to be declared by a typeset statement there's no getting round it. As to what it does, that's best shown by example: So it works a bit like an ordinary array, but the numeric subscript of an ordinary array which would have appeared inside the square bracket is replaced by the string key, in this case two.

The shell will complain if there are an odd number of elements in such a list. This may also be familiar from Perl.

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You can assign values one at a time: Expansion has been held over, but you might like to know about the ways of getting back what you put in. Note they are in random order that's the other main difference from ordinary arrays; associative arrays have no notion of an order unless you explicitly sort them. But here the keys may be just as interesting. You can see that, although the order of the pairs isn't obvious, it's the same each time.

From this example you can work out how to copy an associative array into another one: There are lots of other tricks, but they are mostly associated with clever types of parameter expansion, to be described in chapter 5. Other typeset and type tricks There are variants of typeset, some mentioned sporadically above. There is nothing you can do with any of them that you can't do with typeset that wasn't always the case; we've tried to improve the orthogonality of the options.

They differ in the options which are set by default, and the additional options which are allowed. I won't confuse you by describing all in detail; see the manual. If there is an odd one out, it's export, which not only marks a parameter for export but has the -g flag turned on by default, so that that parameter is not local to the function; in other words, it's equivalent to typeset -gx.

However, one holdover from the days when the options weren't quite so logical is that typeset -x behaves like export, in other words the -g flag is turned on by default. This is partly because in the old days you couldn't export local parameters, so typeset -x either had to turn on -g or turn off -x; that was fixed for the 3. The builtin local is essentially a form of typeset which renounces the -g flag and all its works.

It's possible that you specifically don't want some parameter you make local to have the special property; 3. Internally, the same value as was previously set would continue to be used for finding commands, but it wouldn't be exported.

The second main use of typeset is to set attributes for the parameters. In this case it can operate on an existing parameter, as well as creating a new one. If the parameter didn't exist, it would be created with the usual scoping rules; but if it did exist at the current level of scoping, it would be made readonly with the value assigned to it, meaning you can't set that particular copy of the parameter.

For obvious reasons, it's normal to assign a value to a readonly parameter when you first declare it. Here's a reality check on how this affects scoping: Maybe it's reassuring that the shell can get confused about local parameters, too. I don't find it reassuring in the slightest, since typeset is one of the parts of the code where I tend to fix the bugs, but maybe you do.

Anyway, when the bug is fixed, you should get the output shown, because the first typeset created a local variable which the second typeset made readonly, so that the final assignment caused an error. I mentioned another special typeset option in the previous chapter: This is a one-off; it's the only time typeset takes exactly two parameter names on the command line.

All other uses of typeset take a list of parameters to which any flags given are applied. See the manual for the remaining flags, although most of the more interesting ones have been discussed. The final use of typeset is to list parameters. This can be useful for some of the more enormous parameters, particularly special parameters which I'll talk about in the section in chapter 7 on modules, which tend to swamp the display typeset produces.

Optional: Forcing color output

You can also list parameters of a particular type, by listing the flags you want to know about. For example, typeset -r lists all readonly parameters. Inevitably, the values are read into a parameter. Normally they are taken from standard input, very often the terminal even if you're running a script, unless you redirected the input. The read builtin actually does a bit of processing on the input. It will usually strip any initial or final whitespace spaces or tabs from the line read in, though any in the middle are kept.

You can read a set of values separated by whitespace just by listing the parameters to assign them to; the last parameter gets all the remainder of the line without it being split. Very often it's easiest just to read into an array: It's useful to be able to print a prompt when you want to read something. Please enter a line: Like print, read has a -r flag for raw mode. However, this just has one effect for read: Finally, a more sophisticated note about word-splitting.

I said that, when you are reading to many parameters or an array, the word is split on whitespace. By default and in the vast majority of uses it contains space, tab, newline and a null character character zero: However, you can set it to any string: The read command in zsh doesn't let you do line editing, which some shells do. For that, you should use the vared command, which runs the line editor to edit a parameter, with the -c option, which allows vared to create a new parameter.

It also takes the option -p to specify a prompt, so one of the examples above can be rewritten vared -c -p 'Please enter a line: If you give the option -h historyyou can even retrieve values from previous command lines. It doesn't have all the formatting options of read, however, although when reading an array use the option -a with -c if creating a new array it will perform splitting. Other builtins to control parameters The remaining builtins which handle parameters can be dealt with more swiftly.

Actually, set can also be used to set shell options, either as flags, e. The eval command, described below, gives another way around this. Without an array name, it operates on the positional parameters. You can also give it a number to shift other than one, before the array name.

There is one subtlety to be mentioned here. Normally, unset just makes the parameter named disappear off the face of the earth.

Chapter 3: Dealing with basic shell syntax

However, if you call unset in a function, its ghost lives on in the sense that any parameter you create in the same name will be scoped as the original parameter was. History control commands The easiest way to access the shell's command history is by editing it directly. I talked quite a bit about it in the last chapter, and don't really have anything to add.

Just note that the two other commands based around it are history and r. Job control and process control One of the major contributions of the C-shell was job control. You need to know about foreground and background tasks, and again I introduced these in the last chapter along with the options that control them. Here is an introduction to the relevant builtins. You start a background job in two ways.

In either case, the job then continues without the shell waiting for it.

A User's Guide to the Z-Shell

It will still try and read from or write to the terminal if that's how you started it; you need to use the shell's redirection facilities right at the start if you want to change that, there's nothing you can do after the job has already started. Probably you will only rarely do this with builtins. No other shell, so far as I know, has this feature. A job will stop if it needs to read from the terminal.