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User's Guide to SKSH A ksh-like Shell for the Amiga Version 1.2 (Copyright) 1989 Steve Koren November 19, 1989 Table of Contents Introduction......................................3 Copyright Notice and Other Legal Stuff............4 A Brief History of Unix Shells....................5 SKsh Syntax.......................................6 Credits...........................................8 What SKsh is and is Not...........................9 The Rest of this Document.........................9 SKsh Basics: Executing Commands...................10 SKsh Basics: I/O Redirection......................11 SKsh Basics: Pipe Lines...........................12 SKsh Basics: Strings and Variables................13 SKsh Basics: Parameter Substitution...............15 SKsh Basics: Wildcards............................16 Using SKsh Aliases................................17 Using SKsh Functions..............................18 Function, Alias, Builtin Priority.................20 SKsh Command Substitution.........................21 Control Structures: if-then-elif-else-fi..........23 Control Structures: while-do-done.................24 Control Structures: for-do-done...................25 Test Expressions..................................26 Sub-Shell Execution...............................28 File Name Mapping.................................29 SKsh Scripts......................................30 Command Line Editing and History..................31 Filename Completion...............................34 Index to Users's Guide............................36 SKSH Amiga Shell Page 2 User's Guide Introduction SKsh (Amiga-shell) is a shell designed for the Amiga which closely duplicates functionality of ksh or sh in Unix1. It is designed for programmers and other expert users who feel limited by the Amiga's native shell environment. SKsh provides a very powerful environment; however, it is not for casual workbench users who want a "point and click" interface. SKsh provides a large number of features, some of which have not been previously available in Amiga shells: * Command substitution (using either backtick or $( ) notations) * Shell functions with parameters * Aliases * Local variables, local functions, and local aliases * Powerful control structures and tests * emacs style line editing and history functions * I/O redirection and pipes * A large variety of built-in commands * Unix style wildcards * Unix filename conventions in AmigaDos (such as ../file or ~/file) * Filename completion using <esc><esc> or tab * Coexistence with scripts from other shells 1_____________________Unix is a trademark of AT&T. SKSH Amiga Shell Page 3 User's Guide Copyright Notice and Other Legal Stuff This software is copyright 1989 Steve Koren. It is not public domain; however, it is freely distributable, provided that it is not sold for profit without the written consent of the author. It may be included in compilations of public domain software, freely distributable software, and shareware without written consent of the author provided that no more than $7.00 US 1989 dollars are charged for distribution and disk handling overhead. This and all included documents and works are also copyright 1989 Steve Koren, and are included in the terms of the above paragraph. Any code included with this software may be freely modified. However, further distribution of this modified software is restricted to the condition that a notice of the exact modifications be clearly included with the documentation. The existing documentation may not be modified, only appended to. The sole exception to this rule is that the documentation may be translated to other languages and the original omitted. The porting of this software to other computers than the Commodore Amiga is permitted. The author of this software does not not officially support it. It is provided in the hope that it will be useful, but since it is free, no guarantees of any kind are provided, and you, the user, accept responsibility for its use. SKSH Amiga Shell Page 4 User's Guide A Brief History of Unix Shells Unix has, for a long time, had two standard shells. csh provides a programmable shell, and it is favored by some Unix users because it also provides limited mechanisms for history and command editing. This editing is cumbersome, however, using notations like this: % ^echo^ls -l to edit lines. sh provides a more powerful and intuitive programming environment than csh, so it is preferred for writing scripts. However, it lacks the editing and history facilities of csh. ksh is a newer Unix shell, and is fast becoming the dominant Unix shell. It provides much better editing and history mechanisms than csh, and a more powerful, but upwardly compatible programming environment than sh. This, it has the advantages of both shells. SKsh on the Amiga is patterned closely after ksh, although ksh provides a much more powerful environment than does SKsh. SKSH Amiga Shell Page 5 User's Guide SKsh Syntax If you are familiar with ksh or sh programming under Unix (tm), you will almost immediately become proficient at SKsh. Although SKsh scripts are not compatible (except in some specific cases) with those of sh or ksh, the syntax is nearly identical, and many of the same commands are present. SKsh operation will be discussed in much greater detail later, but some examples are presented here, mainly for those who are already familiar with Unix shells. If you do not understand these examples, this section can be safely ignored. A simple command is a single external function, alias, builtin command, or shell function. For example, "echo foo" is a simple command, as is "a = 42" or "preferences". A control structure is a method of directing execution. Control structures can contain simple commands, other control structures, pipe-lines, or sub-shells. if [ $a -gt 0 ] then while [ $a -lt 10 ] do echo "A = $a" inc a done fi A pipeline is a sequence of simple commands, control structures or sub-shells separated by pipe symbols. A pipe symbol is a vertical bar ('|'). For example, the following is a pipeline: for param in "these" are 'parameters' $boo do echo $param done | wc (notice the pipe symbol in between the for-loop and the word count command). The input or output from a pipe can also be re-directed to or from a file. A subshell is a method of grouping commands, control structures, pipes, or other sub-shells. Sub-shells are delimited by either parentheses: (echo foo; echo bar) or curly-braces: { which emacs; whence emacs } Sub-shells have certain specific uses, and the two forms SKSH Amiga Shell Page 6 User's Guide above differ in their behaviour; this will be explained in greater detail later. Command substitution is a method for including the output of a command as if it was typed into the command line. Again, this will be explained in greater detail later, but here are some examples using both the backtick (`) and the $( ) syntax: a=`basename foo:bar/not/file` or echo $(expr length $(date -y)) A shell function is similar to a script, but it is stored in the shell itself instead of a file. Thus, it can be accessed much faster than a script. Here is a sample function definition: function param_count { echo "$# parameters were passed to this function," echo "the second of which is $2" } Functions can contain local variables, local aliases, and even local functions, as well as any combination of commands and control structures. Functions can call other functions and scripts, as well. An alias is simply a way to save typing effort. An alias can be used to take the place of a command and some of its parameters so that the command is easier to type. For example, alias hist = 'history -e' There are other features as well that will become apparent later. SKSH Amiga Shell Page 7 User's Guide Credits SKsh was developed on and for the Commodore Amiga. SKsh was implemented and debugged entirely with Lattice C 5.02. Aside from a few bugs that cause incorrect code to be generated at times, its a reasonably solid compiler. It has a great debugger, too. SKsh was written and copyrighted by Steve Koren. This manual and the other included documents were written and are copyrighted by Steve Koren. This manual was written using excellence! by MSS. It did all the cool stuff like the table of contents and index. SKsh is freely distributable. The SKsh parser was created using Amiga YACC. This yacc was ported to the Amiga by Bill Lee, and worked great once I recompiled it with larger tables to handle the SKsh grammar. I had expected to have problems with a micro based yacc, but I had none at all. Until SKsh was usable, I used Matt Dillon's shell version 3.01A during SKsh development. I like that shell far better than the normal AmigaDos environment. It provides "real" wildcards, and many other neat things the normal AmigaDos environment does not. A bunch of people on Usenet and at the Cleveland Area Amiga Users's Group have my appreciation for putting up with my silly questions about invoking programs on the Amiga (which turns out, unfortunately, not to be a trivial task). SKsh uses ARP for command execution. There was no other simple way to do it. SKSH Amiga Shell Page 8 User's Guide What SKsh is and is Not SKsh is a powerful alternative to the normal Amigados shell environment. This power comes at a price, however. SKsh is not a tiny program. SKsh is currently about 70 K bytes; small by Unix standards but quite large for AmigaDos. SKsh provides a very similar environment to that found under the two Unix shells mentioned above. It does not claim or attempt to provide an identical environment. Some simple scripts will run under SKsh or ksh, but this fact should not be depended on. In many cases, ksh provides features that SKsh does not. In some cases, SKsh provides features that ksh does not. SKsh is, however, not a general purpose programming language - it is tailored to writing scripts that use other programs and AmigaDos facilities. SKsh is not a speed daemon. It would have been possible to write a much faster programmable shell; however, it would not have provided the ksh-like environment that SKsh does. The SKsh script language is adequately fast for simple tasks, but it is not suitable for complex calculations or algorithms. SKsh is freely distributable software. It is not public domain. No one else may sell SKsh without my written permission, except in the cases detailed in the copyright notice. You are, however, encouraged to distribute SKsh as widely as possible. It is completely free; however, with my other free software package (QRT, a ray tracer) some people sent money anyway. Any money I do receive from SKsh will be used for repair, maintenance, and upgrade of my 2000, and to purchase upgrades to Lattice C and other Amiga software. The Rest of this Document... The rest of this document is an intermediate level tutorial for using SKsh. It assumes that you are familiar with the basic concept and operation of a command interface, such as the AmigaDos CLI. If you are already a user of sh or ksh under Unix, you will probably be able to go through this document very quickly. I do recommend that you read it, though, to see what SKsh does and does not do, and to see what differences there are between SKsh and the Unix shells. The SKsh reference manual explains each command in greater detail, although more concisely. This document does not even come close to covering every SKsh command. It is mean to give you an understanding of the SKsh environment, so that you can examine the reference manual for information on specific commands. SKSH Amiga Shell Page 9 User's Guide SKsh Basics: Executing Commands SKsh can, at the most simple level, be used like the AmigaDos shell. SKsh will display a prompt; exactly what this prompt says can be changed in a number of ways, but by default the prompt contains the current working directory, enclosed in square brackets, followed by a colon, and highlighted, like this: [dh0:usr/graphics]: _ After you see this prompt, you may type commands. It does not matter if these commands are external or internal to SKsh. Multiple commands on may be placed on a line if separated by a semicolon (';'). (Note: a semicolon does not always separate commands. For example, if the semicolon is quoted, it becomes part of a string). In addition, any text after a '#' is taken to be a comment. Previous commands may be recalled and edited for reuse. In addition, they may be searched for in the history list. This will be explained in more detail later; for those who are familiar with the 'emacs' editor from FSF, SKsh duplicates some of those keybindings. In SKsh, pressing control followed by 'c' (^c) will generally abort whatever SKsh is currently doing and return you to the SKsh prompt. For example, if you type 'sleep 6000', SKsh will wait for a very long time before returning to the prompt. You can press ^c to abort this command. However, if an external, non-SKsh command is executing, that command may or may not listen to ^c. SKSH Amiga Shell Page 10 User's Guide SKsh Basics: I/O Redirection The input to or output from commands may be redirected. This is accomplished by using Unix style operators: < = redirect input > = redirect output >> = redirect output, but append Any type of command or statement may be redirected. For example, the following are all equally valid: c:status > outfile sksh_script < infile >outfile while read in_line do echo "Line was: $in_line" done < input_file { echo; version; echo } >> out_file Note in the last two cases that SKsh statements as well as simple commands can use I/O redirection. This is a powerful feature provided by Unix shells, but not, until now, by Amiga shells. SKSH Amiga Shell Page 11 User's Guide SKsh Basics: Pipe Lines A pipe line is simply a series of statements separated by a pipe symbol ('|'). For example, [dh0:]: echo "This is a pipe-line" | wc There can be any number of newlines after the pipe-symbol, but not before it since a newline typically ends a simple statement. Thus, this is legal: [dh0:]: cat my_file.txt | head -20 | xd but this is not: [dh0:]: cat my_file.txt | head -20 | xd since the newline after the 'cat...' terminates the command. Pipes are not limited to simple commands. They may be used with any SKsh statement: [dh0:]: for a in a b c d e > do > echo "a = $a" > done | { read aa; read bb } [dh0:]: echo $aa a = a SKsh was written to operate with the AmigaDos pipe: device, with each branch of the pipe-line executing as a separate process. However, some limitations in the way AmigaDos handles processes made a simple thing very complex. Therefore, the first release of SKsh uses temporary files in the pipe-line instead of true inter-process pipes using the pipe: device. Temporary file pipes are not nearly as useful as interprocess pipes; they are slower, and are limited by the free space on the device used to hold the files. However, at the moment, the capability I need to implement interprocess pipes is simply not there in a useable manner. If the needed capability ever shows up on the Amiga, SKsh is written to take advantage of it, and the code change to do this will be only a few lines. Interprocess pipes using the pipe: device are still usable in the normal manner using multiple CLI windows; it is just not as convenient as the SKsh '|' pipe notation. SKSH Amiga Shell Page 12 User's Guide SKsh Basics: Strings and Variables Strings and variables are basic to the operation of SKsh. A string is simply a sequence of non-special characters, optionally surrounded by single or double quotes. For example, this is a string: howdy A string which contains white space or special characters must be quoted. The most common way to quote a string is to use double quotes: "this string contains spaces and < special | symbols" "this string contains several newline characters" Strings can also be surrounded by single quotes. This has a slightly different meaning; see the section on variables below. A string delimited by doubles quotes can contain the double quote character itself by prefixing it with a backslash: "this string contains \" a double quote" Similarly, a single quoted string can contain a single quote if prefixed by a backslash. There are also several other backslash escapes possible: \n - newline character \t - tab character \f - form feed character \\ - backslash character itself \^ - the caret character Any control character can be included in a string by prefixing it with a caret (^). For example, "^[" is escape. A variable in SKsh is simply a storage place for strings. Any number of variables can be created. Variables can be assigned values using the assignment operator: [dh0:]: my_var="contents of my_var variable" [dh0:]: my_var2 = "more stuff" Note that the second line above, with spaces around the assignment operator, is legal in SKsh, but not in sh or ksh. The SKsh assignment operator is upward compatible with the Unix shells. Variables can be retrieved by prefixing the variable name with SKSH Amiga Shell Page 13 User's Guide a '$'. (In the examples below the results of the commands are indented for clarity). [dh0:]: echo $my_var contents of my_var variable [dh0:]: echo $my_var2 more stuff ("echo" is a command that simply displays its parameters). Variables can also be expanded inside of double quoted strings: [dh0:]: echo "my_var = $my_var" my_var = contents of my_var variable However, variables are not expanded inside of single quoted strings. For example, [dh0:]: echo '$my_var' $my_var would not display the contents of the variable my_var, but rather would display the actual string $my_var, including the '$' symbol. Variables may contain nearly any amount of information. They typically are used to contain only small strings and numbers, but if you wished you could store a whole file in a variable by saying: [dh0:]: big_var = $(cat my_file.txt) (the $( ) notation is simply a way to execute a command and use the output of the command in another command. It will be discussed in more detail later. The above command is equivalent to big_var = `cat my_file`, which may be more familiar to sh users, but the first example above is recommended). SKSH Amiga Shell Page 14 User's Guide SKsh Basics: Parameter Substitution SKsh normally eliminates white space (blanks, newlines and tabs) from between parameters to commands. For example, notice the spacing in the following command and response: [dh0:]: echo notice the spacing here notice the spacing here If you wish to maintain the spacing above, you must put the text in either a single or double quoted string, which causes it to be treated as a single parameter: [dh0:]: echo 'notice this spacing' notice this spacing Even if the string echoed comes from a variable, the same elimination of white space takes place: [dh0:]: a='some text' [dh0:]: echo $a some text If you wish to preserve the spacing, you must enclose the variable in double quotes (remember, variables are expanded in double but not single quotes): [dh0:]: a='some text' [dh0:]: echo "$a" some text (Note for advanced users: this action is actually controlled by a variable called the internal field separator, or IFS.) Internal SKsh commands can have any number of parameters, (until you run out of memory). External commands are limited by the AmigaDos command interpreter, which does not accept commands longer than 256 characters in version 1.3. SKSH Amiga Shell Page 15 User's Guide SKsh Basics: Wildcards SKsh uses Unix style wildcard patterns to match files. The following characters have special meaning: * - matches any number of characters, including zero ? - matches exactly one character [ ] - characters which enclose a character class ! - negate the pattern Since wildcards are expanded by SKsh, and not by the command itself as in AmigaDos, they may be used with any command - even a command such as 'echo' which does not normally deal with files (try echo *). Here are some examples using the first two special types above: a*f matches 'af', 'abf', 'aazzzewerf', etc. a?f matches 'abf', 'acf', but not 'af' or 'aaaf' The square brackets above are used to define a character class. A character class is simply way to specify an exact set of characters. Character classes may contain either a series of enumerated characters, a range of characters, or a negation of any of the above. For example, [abcz] matches the character a, b, c, or z. [a-cv-z] matches either a, b, c, v, w, y, x, or z. [!a-d] matches any character except a, b, c, or d. Character classes may be combined with the * and ? wildcards: [a-c]*.c matches any file starting with a, b, or c and ending with '.c' Wildcards are only expended as normal parameters; that is, outside of quoted strings of any sort. Wildcards also have certain other uses in SKsh besides matching files (for example, see the 'match' or 'set' commands). Wildcards do not have to be used in only the filename component of a path. For example, all of the following are valid wildcard patterns: sys:*/Format sys:System/Fo* mydir/*/*.c *.[hc] Wildcards are currently case-sensitive. (See also: File name mapping) SKSH Amiga Shell Page 16 User's Guide Using SKsh Aliases An 'alias' in SKsh is simply a way to save typing time. An alias can stand for any series of characters. For example, perhaps you enjoy seeing the version number of SKsh. You enjoy it so much, in fact, that you tire of typing 'version' over and over. You can define an alias, called 'v', that simply stands for the 'version' command: [dh0:]: alias v=version [dh0:]: v SKsh Version 1.0, Copyright 1989 Steve Koren You can also include parameters after the alias call. For example: [dh0:]: v -d 19:13:18 Oct 12 1989 The alias command only looks at one parameter after the '=' sign, so to include parameters in the alias, you must enclose the alias definition in quotes: [dh0:]: alias v='version -d' [dh0:]: v 19:13:18 Oct 12 1989 To obtain a list of aliases, simply use the alias command by itself: [dh0:]: alias (big list of aliases) I left out the list of aliases above, because there are a large number supplied by SKsh itself. One of these built in aliases is the unalias command. To find out what the definition of unalias is: [dh0:]: alias unalias unalias = unset -a So, the unalias command simply runs the command 'unset -a'. Unalias is provided as a built in alias, however, since it is easier to remember than unset -a. Unalias removes any number of alias definitions: [dh0:]: unalias v foo bar The above line would remove the alias definitions of v, foo, and bar. Note that alias commands may be used just like any other command, in scripts, functions, or substitution statements. SKSH Amiga Shell Page 17 User's Guide Using SKsh Functions While aliases are limited to simple text substitution uses, functions are vastly more powerful. Functions provide a way to store SKsh programs within SKsh itself instead of in a file. Here is an example function that SKsh loads when it starts up. Don't worry if you don't understand everything in the function definition; it will be explained later in the programming sections. For now, just notice that functions can contain any SKsh statements, and are delimited by curly braces: function path { # set or examine path local comp; if [ $# -eq 0 ] then echo "$PATH" elif [ "$1" = '-add' -o "$1" = 'add' ] then shift for comp in $* do if [ $( expr index "$PATH," "$comp," ) -eq 0 ] then PATH = "$PATH,$comp" fi done else PATH="$1" fi export PATH } That function is one that defines a "path" command in SKsh. Functions may be used like any other command. You do not even have to know that they are functions. For example, the above command, with no parameters, simply prints the path. This can be output to a file, a follows: [dh0:]: path > my_file The path function could also be used in other functions. This provides a very powerful mechanism for extending SKsh. It will be particularly interesting for floppy users who do not want to wait for slow script files. When SKsh functions are executed, several important things happen. All variables, functions, and aliases defined inside the function are local to that function (although this behaviour is changeable in several ways - see the option command). Hence: SKSH Amiga Shell Page 18 User's Guide function outer { function inner { echo "my first parameter is $1" } inner $1 } The function named 'inner' can only be used within the function named 'outer'. You will notice also that a variable called $1 is referenced, but not set. There are several variables that are automatically set by SKsh when a function (or script) is invoked. The most useful are $0, $1, $2, $3, etc. They are set to the parameters passed into the function. Note that $0 is set to the function name itself: [dh0:]: function test1 { > echo "0 = $0, 1 = $1, 2 = $2" > } [dh0:]: test1 foo bar 0 = test1, 1= foo, 2 = bar Also note the ">" marks to the left of the 2nd and 3rd lines of the function. They are the secondary SKsh prompt string, used when it expects more input. You shouldn't type them. SKsh also sets the variable '$#' to the number of parameters passed into the function: [dh0:]: function countp { echo "Number = $#" } [dh0:]: countp "this is all one" another param Number = 3 The variable '$*' is set to the entire parameter list. For example: [dh0:]: function pparams { echo "Args = $*" } [dh0:]: pparams foo bar not Args = foo bar not These standard variables can be modified with the 'shift' command - see the documentation on that command for details. Any functions or aliases used within a function will operate correctly even if they are defined after the function itself. (That is, they are bound dynamically at run-time). This is different than the ksh behavior. SKSH Amiga Shell Page 19 User's Guide Function, Alias, Builtin Priority In SKsh, you can define a function or alias that overrides the definition of a an SKsh builtin command (such as the echo statement). SKsh will evaluate a function definition before an alias with the same name, and an alias before a builtin with the same name. Thus, you can redefine the internal sksh commands. SKsh still provides a mechanism to access the builtin commands, even though you might have redefined them. The force keyword can be used to force the execution of a command as either a function, an alias, or a builtin. For example, say you have redefined the sksh date command with a function, as follows: [dh0:]: function date { > echo 'The date command is not available today.' > } Any future calls to the date command will have the following result: [dh0:]: date The date command is not available today. Suppose, however, that you really did wish to access the date builtin command, and not your function. Use the force keyword with the -b options (for force execution as a builtin): [dh0:]: force -b date Sat Oct 14 11:13:27 1989 This can be particularly useful when you wish to use the original date command inside of your own. Perhaps you wish to define a date command which prints "The year is:" followed by the current year: [dh0:]: function date { > echo -n 'The year is: '; force -b date -y > } [dh0:]: date The years is: 1989 In this case, the force -b command must be used to access the builtin date command. If it was left out, the new date function would be used instead, calling itself recursively. SKsh would eventually detect this situation and issue an error message, but it is not what the command was intended to do. The force keyword also accepts -f and -a parameters, to force execution as a function or alias. SKSH Amiga Shell Page 20 User's Guide SKsh Command Substitution SKsh provides several mechanisms for capturing the output of a statement for subsequent use. The preferred method is to use the following syntax: $(command) SKsh will insert the output of the command as if it was typed in the SKsh command line. Consider an example. The sksh function 'basename' prints the file name part of a path name. For example, [dh0:]: basename sys:path/to/my/file file Now, suppose you wish to obtain the file part of a path string for use in an sksh function. Normally the 'basename' function copies the data to the screen. You want to have it in a variable. If the path you're interested in is in the variable my_path: [dh0:]: bn = $(basename $my_path) The variable 'bn' will contain the desired information. Parameter substitution may be nested. For example, perhaps you wish to obtain the length in characters of the file portion of the path name: [dh0:]: len = $(expr length $(basename $my_path) ) The alternative syntax for command substitution uses backticks: [dh0:]: len = `basename $my_path` However, the first notation is preferred for a number of reasons. Using the backtick notation, SKsh reads the entire substitution command as one token, or set of characters. Tokens in SKsh are limited by the parser to 1024 characters (although strings and variables can be of any length). The parenthetical notation for command substitution has no restrictions on the length of the command enclosed - it could be an entire sksh program. Also, the parenthetical notation is faster than the backtick notation. You will discover that command substitution is a very useful thing to have around. One of the more common uses is the following: [dh0:]: my_program $(which abc) Here, my_program is a program which uses abc in some way (perhaps executes it or edits it). 'abc' is known to be in SKSH Amiga Shell Page 21 User's Guide your SKsh path, but my_program does not know about SKsh paths. The which function in SKsh prints the full path name of a file in the search path, so the above command saves you from having to remember and type the full path. Command substitution works with any SKsh statement. For example: [dh0:]: a = $( for a in a b c > do > echo "a: $a" > done ) [dh0:]: echo "$a" a: a a: b a: c Note that the same variable was used both inside and outside the command substitution. This is ok, since the statement list inside the command substitution marks is completely evaluated before the assignment is made. Command substitution can also be used with external commands. Since external binaries do not support command substitution directly, SKsh stores the results in a temporary file in the 't:' directory. When finished, SKsh deletes the temporary file. 't:' should be assigned to a fast device, such as a ram disk. Actually, a subdirectory on the ram disk is best, so that SKsh's temporary files won't normally be seen. SKSH Amiga Shell Page 22 User's Guide Control Structures: if-then-elif-else-fi SKsh provides a set of control structures for directing execution. The most common of these is the if-then-elif-else- fi statement. It has several forms, but the most common are these: if [ test expression ] then statement list fi The test expression is evaluated (more on test expressions later), and if it is true, the statement list is executed. The if statement can have an else part: if [ expression ] then statement list else statement list fi It can also have any number of else-if expressions: if [ expression ] then stmt_list elif [ expression ] stmt_list else stmt_list fi Any valid SKsh statement list can be used inside the if: if [ $a -lt 10 ] then a = 20 echo "a WAS less than ten, but now it's $a" fi An alternative form of the if statement can be used to test the return code from a command. For example, if cmp -s file1 file2 then echo 'Files are the same' fi If the command following the if keyword returns TRUE (or a zero return code), the if statement proceeds as if an expression returned true. SKSH Amiga Shell Page 23 User's Guide Control Structures: while-do-done A while loop is simply a method for executing a statement list as long as a certain given condition is true. For example, while [ ! -d ram:my_dir ] do sleep 10 done which is an endless loop which waits until a given directory exists (because another process created it). It checks for the existence of ram:my_dir every 10 seconds. (Again test expressions will be explained in detail later). As with if- then-else statements, a while statement can examine the return code from a command. A particularly useful while loop of that form is the following: while read in_line do echo "We read: $in_line" done < input_file That while loop executes as long as the read command returns TRUE. The read command returns FALSE upon reaching the end of the input file, so the loop terminates then. The entire while loop has its input redirected from a given file. In practice, of course, the echo statement would be replaced by the code which accomplishes what you desire. Here is another example, like the above, but which is combined with SKsh command substitution: my_var = $( while read in_line do echo "We Read: $in_line" done < input_file ); That is identical to the above loop, but saves the output in a variable called my_var. You could then echo "$my_var" to retrieve this output. SKSH Amiga Shell Page 24 User's Guide Control Structures: for-do-done SKsh provides a for-do loop, but it differs from the for loops provided with more most programming languages. In SKsh, for loops are used to execute a series of statements for each parameters in a list. For example, for my_param in abc def ghi do echo "my_param = $my_param" done The statement list inside the for loop is executed once for each parameter, and each time, the variable 'my_var' is set to the parameter in question. That is, the first time through the loop, my_var is abc, the second time, def, and the third, ghi. For loops are useful when combined with wildcard patterns: for file in *.c do cp $file dh0:backups/$file.bak done That loop executes once for each c code file in the current directory, copying the file to the directory dh0:backups and adding a '.bak' extension in the process. After you gain experience with SKsh, you will become proficient at executing similar simple programs from the command line. Even though this loop is only four lines, it is quite useful. In fact, it could be shortened to one line by separating the components with ';'. This loop has been extended to also copy .h files: for file in *.c *.h; do cp $file dh0:backups/$file.bak; done For loops can only index parameters. They cannot be used to count. For that, you must use a while loop with the inc or expr function. SKSH Amiga Shell Page 25 User's Guide Test Expressions Test expression are used in if statements and while statements to test a given expression and return TRUE or FALSE appropriately. Test expressions are enclosed in square brackets ('[ ]'). The following simple operators are available: -f fspec TRUE if fspec exists and is a file -d fspec TRUE if fspec exists and is a directory -s fspec TRUE if fspec is a file and has a size of 0 -r fspec TRUE if fspec exists and is readable -w fspec TRUE if fspec exists and is writable -x fspec TRUE if fspec exists and is executable -S fspec TRUE if fspec exists and the script bit is set -P fspec TRUE if fspec exists and the pure bit is set -A fspec TRUE if fspec exists and the archive bit is set -z string TRUE if string has a length of 0 -n string TRUE if string has a non-zero length The following comparison operators are available: n1 -eq n2 TRUE if n1 is numerically equal to n2 n1 -ne n2 TRUE if n1 is numerically unequal to n2 n1 -lt n2 TRUE if n1 is numerically less than n2 n1 -gt n2 TRUE if n1 is numerically greater than n2 n1 -le n2 TRUE if n1 is less than or equal to n2 n1 -gt n2 TRUE if n1 is greater than or equal to n2 s1 = s2 TRUE if s1 is the same string as s2 s1 != s2 TRUE if s1 is not the same string as s2 Also, boolean operators are available: ! e1 TRUE if sub-expression e1 is false e1 -a e2 TRUE if e1 and e2 are both TRUE e1 -o e2 TRUE if e1 or e2 is TRUE Thus, the following expressions are all TRUE: [ 1 -lt 3 ] [ 3 -lt 2 -o 1 -lt 0 -o 3 -eq 3 ] [ -z '' ] [ -n "hi" ] [ ! -z "hi" ] [ a = 'a' ] [ 'xyz' != 'abc' ] [ -d 'c:' ] [ -f 'c:dir' -a -f 's:startup-sequence' ] The boolean and operator has a high precedence than the boolean -o operator. Note also that test expressions do not print their result; they simple set the return code, which can then be tested for. A return code of zero means TRUE. Here is an example usage of a test expression: SKSH Amiga Shell Page 26 User's Guide i = 1 while [ $i -le 10 ] do echo "index variable = $i" inc i done Here is another example: function my_func { if [ $# -ne 3 ] then echo "This function requires exactly 3 parameters" return fi } The inc command is simply a way to increment a variable. There are other ways do it, but inc is the fastest. Test expressions are related to, but should not be confused with, the expr command. SKSH Amiga Shell Page 27 User's Guide Sub-Shell Execution SKsh provides two mechanisms for grouping commands; they are closely related both in behaviour and syntax, but differ in an important way. If a series of statements is grouped within either curly- braces '{ }' or parentheses '( )', that statement list is said to be executed within a sub shell. For example: { echo foo; echo bar } and ( read foo; read bar ) are both sub-shell statements. Subshells group their enclosed commands, so that all the commands within the subshell share a common environment. One use for this is to give all the commands a common input or output. For example: { c:status echo "Done with status command" c:dir echo "Done with dir command" } > out_file The output of all the commands within the subshell goes to a common file. This works for input, as well: { read foo; read bar } < in_file If you tried to redirect the input of each read command separately, both 'foo' and 'bar' would contain the same information. By using a sub-shell, the reads are sequential from the input file. The parenthetical subshell syntax differs from the above form only in that any variables declared within the subshell are local. For example, [dh0:] answer = 42; echo $answer 42 [dh0:]: ( answer = 7; echo $answer ) 7 [dh0:]: echo $answer 42 Notice that the answer variable is 42 both before and after the subshell, but is 7 within it. Because this type of subshell allocates space for local variables, the first form is both faster and uses less memory. It is the preferred form, unless you do in fact need local variables. (Functions and aliases declared within the parenthetical subshell are local as well). SKSH Amiga Shell Page 28 User's Guide File Name Mapping When SKsh sees an unquoted file name, it maps the file name from a Unix style file name to an AmigaDos style file name. The Unix style has several advantages. First and foremost, a single dot ('.') can be used to specify the current working directory. For example, [dh0:]: assign this_dir: . [dh0:]: HOME=. assigns 'this_dir' (a device) to the current working directory, and then sets the SKsh home directory to the current directory. The dot can be used in any command, such as 'cp' or 'mv', but it cannot be quoted or it looses its magic properties and becomes just a dot. For example, [dh0:]: echo . dh0:appl/excellence!/documents/SKSH [dh0:]: echo "." . In addition, a path beginning with a slash ('/') will be mapped by SKsh to be an AmigaDos absolute path name instead of a relative path name. For example, run lse /usr/src/SKsh/Parser.y really edits the file 'dh0:usr/src/SKsh/Parser.y' if the current device is dh0:. Also, SKsh maps two sequential dots ('..') to be the parent directory of the current directory (which in AmigaDos is specified with a slash): run emacs ../../my_file.c The file my_file.c in the directory two levels above the current directory is loaded into emacs. A tilde ('~') can be used to specify the contents of the HOME variable. For example, if HOME is 'sys:usr/src/SKsh', [dh0:]: echo ~/Parser.y sys:usr/src/SKsh/Parser.y SKsh can be instructed not to perform this file name mapping. See the options command for details. SKSH Amiga Shell Page 29 User's Guide SKsh Scripts If a file containing SKsh commands is in the SKsh search path, and has its script bit set, SKsh will execute the file directly as if it was a binary file; there is no need to use an "execute" or other special command. Normally, SKsh executes the file in its own sub-shell. Thus, variables, functions, and aliases defined within the script file are local. SKsh can also "source" files (execute them but not in a subshell). SKsh will happily co-exist with scripts from other shells. If SKsh detects a file with the script bit set, it first examines the first two characters of the file. If they are '#!' or ';!' SKsh reads the rest of the first line, appends the name of the script file, and passes the string to AmigaDos to be executed. For example, on my system I have scripts from SKsh, Matt Dillon's shell, and the AmigaDos "execute" command. My scripts either begin with: #!sys:bin/shell if the script is to be executed by Matt's shell, or ;!c:execute if the file is an "execute" script. Since the first character is recognized by the appropriate shell as a comment, the script runs fine, and SKsh knows to pass execution to the correct shell. It is important that there are no leading blanks or newlines before the '#!' or ';!'; they must be the first two characters of the file. This mechanism can be used with any other Amiga shell that recognizes '#' or ';' as a comment character. If the script bit is not set, SKsh will ignore the file unless you explicitly use the 'source' command. Also, if the shell does not automatically exit after executing the script, you must include an explicit exit statement at the end of the script (such as with Matt Dillon's Shell). (Note: there seems to be a bug someplace with using ;!execute for AmigaDos execute scripts. It seems that execute sometimes returns before the script has finished running, and things tend to get a bit confused. I do not think this is an SKsh problem, since I run the execute command the same way as I run anything else). SKSH Amiga Shell Page 30 User's Guide Command Line Editing and History SKsh provides mechanisms for recalling and editing previous commands. To obtain a list of previous commands, use the history command. By default, SKsh keeps the previous 32 commands, although this number can be changed by setting the HISTSIZE variable. In addition, command line editing is available (but can be turned off - see the options command). The following keys have special meaning (the caret mark means hold down the control key and press the following character): ^p or up arrow - recall previous command ^n or down arrow - recall next command ^b or left arrow - move cursor left ^f or right arrow - move cursor right ^m or return - accept and execute current line ^a or shift-left - move to beginning of line ^e or shift-right - move to end of line ^k - kill to end of line ^l - redraw the current line ^d or delete key - delete current character ^h or backspace - delete previous character esc-f - move forward one word esc-b - move backward one word esc-d - delete the next word esc-backspace - delete the previous word esc-< or shift-up - move to first line in history esc-> or shift-down - move to last line in history esc-esc or tab - filename completion esc-= - List matching file names esc-* - Insert matching file names esc-. - Insert last param of prev line ^r - reverse search for line ^o - execute line, move to next ^u - multiply next command by 4 function keys - insert defined text The basic editing commands are self explanatory, but the others may not be. The reverse search command is used to search for a string in the history list, and then display the line containing that string for further editing. For example, suppose your history list contained 4 lines, as follows: [dh0]: history 1: echo 'This is a test' 2: version 3: date 4: history Then, at the SKsh prompt, type a substring from any previous command: SKSH Amiga Shell Page 31 User's Guide [dh0:]: test When you press ^r, the most recent line containing the substring will be displayed and available for editing: [dh0:]: echo 'This is a test' This line can be edited, or accepted as is by pressing return. If it is not the correct line, pressing ^r yet again will start the reverse search again beginning with the line previous to the one displayed. Thus, multiple ^r's can be used to access the desired line. If the line is changed in any way, it will be re-entered at bottom of the history list as a new command. If it is not edited, it will simply be executed, but not inserted again into the history list (although this behaviour can be changed with the options command. The ^o key is useful for executing a series of commands multiple times. Suppose your history list looks like this: 1: echo $HISTSIZE 2: date 3: echo 'command 1' 4: echo 'command 2' 5: echo 'command 3' Use the ^p key or up arrow to move to the 3rd line. By pressing the ^o key, that line is executed, and SKsh remembers which line that was. By pressing ^o again, the next line is executed. Upon reaching the end of the list, SKsh moves to the first line upon which ^o was used. In this manner, 'command 1', 'command 2', and 'command 3' would be echoed repeatedly. Using any other movement or editing command will cause SKsh to forget which line was the first, and you will have to move to it again. The ^u key causes the next command to be repeated four times. For example, pressing ^u followed by the '-' key inserts four dashes. Pressing ^u followed by the delete key deletes four characters. The action of ^u is recursive; two ^u's in a row will repeat the next command 16 times. Three would repeat 64 times. Therefore, to insert a row of 64 dashes, use '^u^u^u-'. If you press a function key, SKsh will examine the contents of the variable with the same name. For example, pressing f1 would cause SKsh to look for a variable named 'f1', and if found, insert the text it contains as if you had typed it. If the text ends in a newline, SKsh will execute the command immediately; otherwise, it will simply display it for editing or execution. For example: SKSH Amiga Shell Page 32 User's Guide [dh0:]: f1="echo testing" would would just display "echo testing" when f1 is pressed, but: [dh0:]: f1="echo testing\n" would execute the command as well. <esc>. will insert the last parameter of the previous line. For example, suppose you have typed: [dh0:]: ll some_file_name Now, you can type: [dh0:]: rm and press <esc>., which will insert some_file_name: [dh0:]: rm some_file_name In addition to the interactive editing facilities, a single command can be executed with the 'history -e' command. You can specify either a substring of the command, its absolute number, or its relative number by using a negative offset. For example, given the above history list, all of the following would echo 'command 2': [dh0:]: history -e 'd 2' [dh0:]: history -e 4 [dh0:]: history -e -2 The executed command is not placed at the end of the history list (see the options command). For convenience, 'history -e' has been aliased to '!'. Also, 'history -e -1' has been aliased to '!!' (similar to csh, except that in SKsh there must be a space between the '!' and the parameter). If you type a command line that would wrap onto the next line, SKsh will instead scroll the line 12 characters to the left and let you continue typing. If you move off either side of the "sliding window", sksh will adjust the line accordingly. If this behaviour does not appear to be acting correctly, check the value of the COLUMNS and PNPC variables, described in the Reference Manual. The COLUMNS variable should be set to the number of columns in the current window, and PNPC should be set to the number of non-printable ANSI control characters in the SKsh prompt (21 for the default prompt). If either of these numbers are wrong, long lines will display improperly. Also, SKsh line editing can be turned off completely; see the options command for details. In this case, no line scrolling is performed. If the COLUMNS variable is set to less than 15, SKsh will get confused. SKSH Amiga Shell Page 33 User's Guide Filename Completion SKsh supports filename completion using <esc><esc> or tab. For example, suppose your current working directory contains the following files: my_file.c another_c_file.c this_is_a_long_filename test_file2 test_file3 picture.ham picture1.ham picture2.ham If SKsh command line editing is turned on (see the options command), you can insert any file name into the command line by typing part of the file name and pressing the escape key twice. For example, suppose you typed: [dh0:]: cat ano and pressed <esc><esc>. SKsh would fill in the rest of the file name for you: [dh0:]: cat another_c_file.c In fact, since 'a' is enough to uniquely specify the file name, you could have typed 'a<esc><esc>' for the same effect. In the case of 'test_file2' and 'test_file3' above, typing 'te' is not enough to uniquely specify the file, but SKsh will help here too by filling in as much as it can: [dh0:]: echo te (press <esc><esc>) [dh0:]: echo test_file You would then have to type either '2' or '3', but you have still saved 7 characters of typing. Filename completion is useful not only to save typing, but to insure that you have not mis-typed the file name. You can use filename completion on paths, as well: [dh0:]: sys:S (press <esc><esc>) [dh0:]: sys:System/Fo (type /Fo and <esc><esc) [dh0:]: sys:System/Format The tab key can also be used for filename completion if the proper option to SKsh is set (see the options command). SKSH Amiga Shell Page 34 User's Guide Case is significant in filename completion. Also, if file name mapping is enabled (see the options command), it will be performed on the current file name, if applicable. Thus, '/System/Fo' will be changed to ':System/Format' (notice the first slash is changed to a colon). In SKsh 1.1 or later, there are two additional filename completion features. You can type a partial filename (optionally using wildcard patterns), press <esc>=, and SKsh will list all matching files as if an '*' were appended to the filename you typed. It will the re-display your command line so you can continue typing: [dh0:]: show pic ( press <esc>=) 1) picture.ham 2) picture1.ham 3) picture2.ham [dh0:]: show pic You can then continue typing, but you can see the matching files. This is useful when you have typed part of a command, and then think 'Hmm, what was that file called?'. The filename you type can contain wilcard patterns, as well. Also in SKsh 1.1 or later, <esc>* will insert matching file names in the command line. Again, given the above example, you could type [dh0:]: show *.ham and press <esc>*. SKsh will re-write the command line as follows: [dh0:]: show picture.ham picture1.ham picture2.ham Using <esc>*, the pattern must match the files exactly; SKsh does not append a '*' for you as it does with <esc>=. SKsh is, I believe, the first Amiga shell to offer filename completion. You'll find it addictive. It works best with hard or ram disks, since the directory seek speed is faster. SKSH Amiga Shell Page 35 User's Guide Index to Users's Guide $# 7, 18-19, 27 $( 3, 7, 14, 18, 21-22, 24 $* 18-19 $0 19 $1 18-19 $2 7, 19 ( ) 3, 7, 14, 28 -a 10, 17-18, 20, 26 -d fspec 26 -eq 18, 26 -f fspec 26 -gt 6, 26 -le 26-27 -lt 6, 23, 26 -n string 26 -ne 26-27 -o 18, 26 -r fspec 26 -s fspec 26 -w fspec 26 -x fspec 26 -z string 26 <esc><esc> 3, 34 alias 2-3, 6-7, 17-20, 28, 30, 33 append 4, 11, 30 assignment 13, 22 backspace 31 backticks 21 blanks 15, 30 boolean operators 26 character class 16 COLUMNS 33 Command Substitution 2-3, 7, 21-22, 24 comment 10, 30 comparison operators 26 Control Structures 2-3, 6-7, 23-25 Copyright 1-2, 4, 8-9, 17 csh 5, 33 curly braces 18 current working directory 10, 29, 34 do 2-6, 8-16, 18-20, 22, 24-31, 33 done 2, 6, 11-12, 18, 22, 24-25, 27-28 dot 29 double quotes 13, 15 down arrow 31 echo 5-7, 11-12, 14-16, 18-20, 22-25, 27-29, 31-34 elif 2, 18, 23 else 2, 9, 18, 23-24 emacs 3, 6, 10, 29 enumerated characters 16 esc-b 31 SKSH Amiga Shell Page 36 User's Guide esc-f 31 excellence! 8, 29 executable 26 Executing Commands 2, 10 expr 2, 7, 18, 21, 23-27 extending SKsh 18 fi 2-4, 6-7, 9, 11-32, 34-35 File Name Mapping 2, 16, 29, 35 Filename Completion 2-3, 31, 34-35 for 1-26, 28-35 force 20 function 2-3, 6-7, 17-22, 25, 27-28, 30-32 function name 19 functions 2-3, 7, 17-19, 28, 30 history 2-3, 5, 7, 10, 31-33 HISTSIZE 31-32 I/O Redirection 2-3, 11 if 2, 4, 6-7, 9-10, 12-16, 18-21, 23- 30, 32-35 IFS 15 inc 4, 6-8, 12-14, 16-17, 22, 25, 27, 30, 34-35 index parameters 25 input 6, 11, 19, 24, 28 internal field separator 15 ksh 1, 3, 5-6, 9, 13, 19 Lattice 8-9 line editing 2-3, 31, 33-34 list of aliases 17 local 3, 7, 18, 28, 30 more input 19 newlines 12, 15, 30 number of parameters 15, 19 parameter list 19 Parameter Substitution 2, 15, 21 parameters 3, 6-7, 14-20, 25, 27 path 16, 18, 21-22, 29-30, 34 Pipe Lines 2, 12 pipeline 6 PNPC 33 Priority 2, 20 range of characters 16 read 6, 9, 11-12, 21, 24, 26, 28, 30 readable 26 return code 23-24, 26 reverse search 31-32 right arrow 31 secondary SKsh prompt string 19 semicolon 10 set of characters 16, 21 sh 1-25, 27-35 shift 18-19 simple command 6, 11-12 simple operators 26 SKSH Amiga Shell Page 37 User's Guide single parameter 15 single quotes 13, 15 slash 13, 29, 35 sleep 10, 24 slow script files 18 string 2, 10, 13-16, 19, 21, 26, 30-31, 33 sub shell 28 subshell 6, 28, 30 tabs 15 test expression 2, 23-24, 26-27 then 2, 6, 18, 23-24, 26-27, 29, 31, 34 token 21 unalias 17 up arrow 31-32 variable 2-3, 7, 13-15, 18-19, 21-22, 24- 25, 27-33 which 3, 6-8, 13-16, 20-22, 24, 26, 29, 32 while 2, 6, 11, 18, 24-27 white space 13, 15 Wildcards 2-3, 8, 16 writable 26 [ ] 16, 26 ^a 31 ^b 31 ^d 31 ^e 5, 31 ^f 31 ^h 31 ^k 31 ^l 5, 31 ^m 31 ^n 31 ^o 31-32 ^p 31-32 ^r 31-32 { } 28 SKSH Amiga Shell Page 38 User's Guide