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diff --git a/lib/stdlib/doc/src/shell.xml b/lib/stdlib/doc/src/shell.xml index 65c441203c..d6e8036d4e 100644 --- a/lib/stdlib/doc/src/shell.xml +++ b/lib/stdlib/doc/src/shell.xml @@ -24,87 +24,96 @@ <title>shell</title> <prepared>Bjorn Gustavsson</prepared> - <responsible>Bjarne Dacker</responsible> + <responsible>Bjarne Däcker</responsible> <docno>1</docno> <approved>Bjarne Däcker</approved> <checked></checked> - <date>97-01-24</date> + <date>1997-01-24</date> <rev>A</rev> - <file>shell.sgml</file> + <file>shell.xml</file> </header> <module>shell</module> - <modulesummary>The Erlang Shell</modulesummary> + <modulesummary>The Erlang shell.</modulesummary> <description> - <p>The module <c>shell</c> implements an Erlang shell. - </p> - <p>The shell is a user interface program + <p>This module provides an Erlang shell.</p> + + <p>The shell is a user interface program for entering expression sequences. The expressions are - evaluated and a value is returned. + evaluated and a value is returned. A history mechanism saves previous commands and their values, which can then be incorporated in later commands. How many commands and results to save can be determined by the user, - either interactively, by calling <c>shell:history/1</c> and - <c>shell:results/1</c>, or by setting the application configuration + either interactively, by calling + <seealso marker="#history/1"><c>history/1</c></seealso> and + <seealso marker="#results/1"><c>results/1</c></seealso>, + or by setting the application configuration parameters <c>shell_history_length</c> and - <c>shell_saved_results</c> for the application STDLIB. - </p> - <p>The shell uses a helper process for evaluating commands in - order to protect the history mechanism from exceptions. By + <c>shell_saved_results</c> for the STDLIB application.</p> + + <p>The shell uses a helper process for evaluating commands + to protect the history mechanism from exceptions. By default the evaluator process is killed when an exception - occurs, but by calling <c>shell:catch_exception/1</c> or by + occurs, but by calling <seealso marker="#catch_exception/1"> + <c>catch_exception/1</c></seealso> or by setting the application configuration parameter - <c>shell_catch_exception</c> for the application STDLIB - this behavior can be changed. See also the example below. - </p> + <c>shell_catch_exception</c> for the STDLIB application + this behavior can be changed. See also the example below.</p> + <p>Variable bindings, and local process dictionary changes - which are generated in user expressions are preserved, and the variables + that are generated in user expressions are preserved, and the variables can be used in later commands to access their values. The - bindings can also be forgotten so the variables can be re-used. - </p> + bindings can also be forgotten so the variables can be reused.</p> + <p>The special shell commands all have the syntax of (local) function calls. They are evaluated as normal function calls and many commands can be used in one - expression sequence. - </p> + expression sequence.</p> + <p>If a command (local function call) is not recognized by the - shell, an attempt is first made to find the function in the + shell, an attempt is first made to find the function in module <c>user_default</c>, where customized local commands - can be placed. If found, then the function is evaluated. - Otherwise, an attempt is made to evaluate the function in the - module <c>shell_default</c>. The module - <c>user_default</c> must be explicitly loaded. - </p> + can be placed. If found, the function is evaluated, + otherwise an attempt is made to evaluate the function in + module <c>shell_default</c>. Module + <c>user_default</c> must be explicitly loaded.</p> + <p>The shell also permits the user to start multiple concurrent - jobs. A job can be regarded as a set of processes which can - communicate with the shell. - </p> + jobs. A job can be regarded as a set of processes that can + communicate with the shell.</p> + <p>There is some support for reading and printing records in the shell. During compilation record expressions are translated to tuple expressions. In runtime it is not known whether a tuple - actually represents a record. Nor are the record definitions - used by compiler available at runtime. So in order to read the + represents a record, and the record definitions + used by the compiler are unavailable at runtime. So, to read the record syntax and print tuples as records when possible, record - definitions have to be maintained by the shell itself. The shell - commands for reading, defining, forgetting, listing, and - printing records are described below. Note that each job has its - own set of record definitions. To facilitate matters record - definitions in the modules <c>shell_default</c> and + definitions must be maintained by the shell itself.</p> + + <p>The shell commands for reading, defining, forgetting, listing, and + printing records are described below. Notice that each job has its + own set of record definitions. To facilitate matters, record + definitions in modules <c>shell_default</c> and <c>user_default</c> (if loaded) are read each time a new job is - started. For instance, adding the line</p> + started. For example, adding the following line + to <c>user_default</c> makes the definition of <c>file_info</c> + readily available in the shell:</p> + <code type="none"> - -include_lib("kernel/include/file.hrl").</code> - <p>to <c>user_default</c> makes the definition of <c>file_info</c> - readily available in the shell. - </p> - <p>The shell runs in two modes: </p> +-include_lib("kernel/include/file.hrl").</code> + + <p>The shell runs in two modes:</p> + <list type="bulleted"> - <item><c>Normal (possibly restricted)</c> mode, in which - commands can be edited and expressions evaluated. + <item> + <p><c>Normal (possibly restricted)</c> mode, in which + commands can be edited and expressions evaluated</p> </item> - <item>Job Control Mode <c>JCL</c>, in which jobs can be - started, killed, detached and connected. + <item> + <p>Job Control Mode, <c>JCL</c>, in which jobs can be + started, killed, detached, and connected</p> </item> </list> + <p>Only the currently connected job can 'talk' to the shell.</p> </description> @@ -117,60 +126,51 @@ </item> <tag><c>f()</c></tag> <item> - <p>Removes all variable bindings. - </p> + <p>Removes all variable bindings.</p> </item> <tag><c>f(X)</c></tag> <item> - <p>Removes the binding of variable <c>X</c>. - </p> + <p>Removes the binding of variable <c>X</c>.</p> </item> <tag><c>h()</c></tag> <item> - <p>Prints the history list. - </p> + <p>Prints the history list.</p> </item> <tag><c>history(N)</c></tag> <item> <p>Sets the number of previous commands to keep in the history list to <c>N</c>. The previous number is returned. - The default number is 20. - </p> + Defaults to 20.</p> </item> <tag><c>results(N)</c></tag> <item> <p>Sets the number of results from previous commands to keep in the history list to <c>N</c>. The previous number is returned. - The default number is 20. - </p> + Defaults to 20.</p> </item> <tag><c>e(N)</c></tag> <item> - <p>Repeats the command <c>N</c>, if <c>N</c> is positive. If + <p>Repeats command <c>N</c>, if <c>N</c> is positive. If it is negative, the <c>N</c>th previous command is repeated - (i.e., <c>e(-1)</c> repeats the previous command). - </p> + (that is, <c>e(-1)</c> repeats the previous command).</p> </item> <tag><c>v(N)</c></tag> <item> - <p>Uses the return value of the command <c>N</c> in the + <p>Uses the return value of command <c>N</c> in the current command, if <c>N</c> is positive. If it is negative, the return value of the <c>N</c>th previous command is used - (i.e., <c>v(-1)</c> uses the value of the previous command). - </p> + (that is, <c>v(-1)</c> uses the value of the previous command).</p> </item> <tag><c>help()</c></tag> <item> - <p>Evaluates <c>shell_default:help()</c>. - </p> + <p>Evaluates <c>shell_default:help()</c>.</p> </item> <tag><c>c(File)</c></tag> <item> <p>Evaluates <c>shell_default:c(File)</c>. This compiles and loads code in <c>File</c> and purges old versions of code, if necessary. Assumes that the file and module names - are the same. - </p> + are the same.</p> </item> <tag><c>catch_exception(Bool)</c></tag> <item> @@ -179,161 +179,264 @@ (<c>false</c>) is to kill the evaluator process when an exception occurs, which causes the shell to create a new evaluator process. When the exception handling is set to - <c>true</c> the evaluator process lives on which means that - for instance ports and ETS tables as well as processes - linked to the evaluator process survive the exception. - </p> + <c>true</c>, the evaluator process lives on. This means, + for example, that ports and ETS tables as well as processes + linked to the evaluator process survive the exception.</p> </item> <tag><c>rd(RecordName, RecordDefinition)</c></tag> <item> <p>Defines a record in the shell. <c>RecordName</c> is an atom and <c>RecordDefinition</c> lists the field names and the default values. Usually record definitions are made - known to the shell by use of the <c>rr</c> commands + known to the shell by use of the <c>rr/1,2,3</c> commands described below, but sometimes it is handy to define records - on the fly. - </p> + on the fly.</p> </item> <tag><c>rf()</c></tag> <item> <p>Removes all record definitions, then reads record definitions from the modules <c>shell_default</c> and <c>user_default</c> (if loaded). Returns the names of the - records defined. - </p> + records defined.</p> </item> <tag><c>rf(RecordNames)</c></tag> <item> <p>Removes selected record definitions. <c>RecordNames</c> is a record name or a list of record names. - Use <c>'_'</c> to remove all record definitions. - </p> + To remove all record definitions, use <c>'_'</c>.</p> </item> <tag><c>rl()</c></tag> <item> - <p>Prints all record definitions. - </p> + <p>Prints all record definitions.</p> </item> <tag><c>rl(RecordNames)</c></tag> <item> <p>Prints selected record definitions. - <c>RecordNames</c> is a record name or a list of record names. - </p> + <c>RecordNames</c> is a record name or a list of record names.</p> </item> <tag><c>rp(Term)</c></tag> <item> <p>Prints a term using the record definitions known to the shell. All of <c>Term</c> is printed; the depth is not - limited as is the case when a return value is printed. - </p> + limited as is the case when a return value is printed.</p> </item> <tag><c>rr(Module)</c></tag> <item> <p>Reads record definitions from a module's BEAM file. If there are no record definitions in the BEAM file, the source file is located and read instead. Returns the names - of the record definitions read. <c>Module</c> is an atom. - </p> + of the record definitions read. <c>Module</c> is an atom.</p> </item> <tag><c>rr(Wildcard)</c></tag> <item> <p>Reads record definitions from files. Existing definitions of any of the record names read are replaced. <c>Wildcard</c> is a wildcard string as defined in - <c>filelib(3)</c> but not an atom. - </p> + <seealso marker="filelib"><c>filelib(3)</c></seealso>, + but not an atom.</p> </item> <tag><c>rr(WildcardOrModule, RecordNames)</c></tag> <item> <p>Reads record definitions from files but discards record names not mentioned in <c>RecordNames</c> (a - record name or a list of record names). - </p> + record name or a list of record names).</p> </item> <tag><c>rr(WildcardOrModule, RecordNames, Options)</c></tag> <item> <p>Reads record definitions from files. The compiler options <c>{i, Dir}</c>, <c>{d, Macro}</c>, and <c>{d, Macro, Value}</c> are recognized and used - for setting up the include path and macro definitions. Use - <c>'_'</c> as value of <c>RecordNames</c> to read all record - definitions. - </p> + for setting up the include path and macro definitions. + To read all record definitions, use + <c>'_'</c> as value of <c>RecordNames</c>.</p> </item> </taglist> </section> <section> <title>Example</title> - <p>The following example is a long dialogue with the shell. Commands + <p>The following example is a long dialog with the shell. Commands starting with <c>></c> are inputs to the shell. All other lines - are output from the shell. All commands in this example are explained at the end of the dialogue. - .</p> + are output from the shell.</p> + <pre> strider 1> <input>erl</input> Erlang (BEAM) emulator version 5.3 [hipe] [threads:0] Eshell V5.3 (abort with ^G) -1><input>Str = "abcd".</input> -"abcd" +1> <input>Str = "abcd".</input> +"abcd"</pre> + + <p>Command 1 sets variable <c>Str</c> to string <c>"abcd"</c>.</p> + + <pre> 2> <input>L = length(Str).</input> -4 +4</pre> + + <p>Command 2 sets <c>L</c> to the length of string <c>Str</c>.</p> + + <pre> 3> <input>Descriptor = {L, list_to_atom(Str)}.</input> -{4,abcd} +{4,abcd}</pre> + + <p>Command 3 builds the tuple <c>Descriptor</c>, evaluating the BIF + <seealso marker="erts:erlang#list_to_atom/1"><c>list_to_atom/1</c> + </seealso>.</p> + + <pre> 4> <input>L.</input> -4 +4</pre> + + <p>Command 4 prints the value of variable <c>L</c>.</p> + + <pre> 5> <input>b().</input> Descriptor = {4,abcd} L = 4 Str = "abcd" -ok +ok</pre> + + <p>Command 5 evaluates the internal shell command <c>b()</c>, which + is an abbreviation of "bindings". This prints + the current shell variables and their bindings. <c>ok</c> at + the end is the return value of function <c>b()</c>.</p> + + <pre> 6> <input>f(L).</input> -ok +ok</pre> + + <p>Command 6 evaluates the internal shell command <c>f(L)</c> (abbreviation + of "forget"). The value of variable <c>L</c> is removed.</p> + + <pre> 7> <input>b().</input> Descriptor = {4,abcd} Str = "abcd" -ok +ok</pre> + + <p>Command 7 prints the new bindings.</p> + + <pre> 8> <input>f(L).</input> -ok +ok</pre> + + <p>Command 8 has no effect, as <c>L</c> has no value.</p> + + <pre> 9> <input>{L, _} = Descriptor.</input> -{4,abcd} +{4,abcd}</pre> + + <p>Command 9 performs a pattern matching operation on + <c>Descriptor</c>, binding a new value to <c>L</c>.</p> + + <pre> 10> <input>L.</input> -4 +4</pre> + + <p>Command 10 prints the current value of <c>L</c>.</p> + + <pre> 11> <input>{P, Q, R} = Descriptor.</input> -** exception error: no match of right hand side value {4,abcd} +** exception error: no match of right hand side value {4,abcd}</pre> + + <p>Command 11 tries to match <c>{P, Q, R}</c> against + <c>Descriptor</c>, which is <c>{4, abc}</c>. The match fails and + none of the new variables become bound. The printout starting + with "<c>** exception error:</c>" is not the value of the + expression (the expression had no value because its evaluation + failed), but a warning printed by the system to inform + the user that an error has occurred. The values of the other + variables (<c>L</c>, <c>Str</c>, and so on) are unchanged.</p> + + <pre> 12> <input>P.</input> -* 1: variable 'P' is unbound ** +* 1: variable 'P' is unbound 13> <input>Descriptor.</input> -{4,abcd} +{4,abcd}</pre> + + <p>Commands 12 and 13 show that <c>P</c> is unbound because the + previous command failed, and that <c>Descriptor</c> has not + changed.</p> + + <pre> 14><input>{P, Q} = Descriptor.</input> {4,abcd} 15> <input>P.</input> -4 +4</pre> + + <p>Commands 14 and 15 show a correct match where <c>P</c> and + <c>Q</c> are bound.</p> + + <pre> 16> <input>f().</input> -ok +ok</pre> + + <p>Command 16 clears all bindings.</p> + + <p>The next few commands assume that <c>test1:demo(X)</c> is + defined as follows:</p> + + <p><c>demo(X) -></c><br></br> + <c>put(aa, worked),</c><br></br> + <c>X = 1,</c><br></br> + <c>X + 10.</c></p> + + <pre> 17> <input>put(aa, hello).</input> undefined 18> <input>get(aa).</input> -hello +hello</pre> + + <p>Commands 17 and 18 set and inspect the value of item + <c>aa</c> in the process dictionary.</p> + + <pre> 19> <input>Y = test1:demo(1).</input> -11 +11</pre> + + <p>Command 19 evaluates <c>test1:demo(1)</c>. The evaluation + succeeds and the changes made in the process dictionary become + visible to the shell. The new value of dictionary item + <c>aa</c> can be seen in command 20.</p> + + <pre> 20> <input>get().</input> [{aa,worked}] 21> <input>put(aa, hello).</input> worked 22> <input>Z = test1:demo(2).</input> ** exception error: no match of right hand side value 1 - in function test1:demo/1 + in function test1:demo/1</pre> + + <p>Commands 21 and 22 change the value of dictionary item + <c>aa</c> to <c>hello</c> and call <c>test1:demo(2)</c>. Evaluation + fails and the changes made to the dictionary in + <c>test1:demo(2)</c>, before the error occurred, are discarded.</p> + + <pre> 23> <input>Z.</input> -* 1: variable 'Z' is unbound ** +* 1: variable 'Z' is unbound 24> <input>get(aa).</input> -hello +hello</pre> + + <p>Commands 23 and 24 show that <c>Z</c> was not bound and that + dictionary item <c>aa</c> has retained its original value.</p> + + <pre> 25> <input>erase(), put(aa, hello).</input> undefined 26> <input>spawn(test1, demo, [1]).</input> <0.57.0> 27> <input>get(aa).</input> -hello +hello</pre> + + <p>Commands 25, 26, and 27 show the effect of evaluating + <c>test1:demo(1)</c> in the background. In this case, the + expression is evaluated in a newly spawned process. Any + changes made in the process dictionary are local to the newly + spawned process and therefore not visible to the shell.</p> + + <pre> 28> <input>io:format("hello hello\n").</input> hello hello ok @@ -341,31 +444,96 @@ ok hello hello ok 30> <input>v(28).</input> -ok +ok</pre> + + <p>Commands 28, 29 and 30 use the history facilities of the shell. + Command 29 re-evaluates command 28. Command 30 uses the value (result) + of command 28. In the cases of a pure function (a function + with no side effects), the result is the same. For a function + with side effects, the result can be different.</p> + + <p>The next few commands show some record manipulation. It is + assumed that <c>ex.erl</c> defines a record as follows:</p> + + <p><c>-record(rec, {a, b = val()}).</c></p> + <p><c>val() -></c><br></br> + <c>3.</c></p> + + <pre> 31> <input>c(ex).</input> {ok,ex} 32> <input>rr(ex).</input> -[rec] +[rec]</pre> + + <p>Commands 31 and 32 compile file <c>ex.erl</c> and read + the record definitions in <c>ex.beam</c>. If the compiler did not + output any record definitions on the BEAM file, <c>rr(ex)</c> + tries to read record definitions from the source file instead.</p> + + <pre> 33> <input>rl(rec).</input> -record(rec,{a,b = val()}). -ok +ok</pre> + + <p>Command 33 prints the definition of the record named + <c>rec</c>.</p> + + <pre> 34> <input>#rec{}.</input> -** exception error: undefined shell command val/0 +** exception error: undefined shell command val/0</pre> + + <p>Command 34 tries to create a <c>rec</c> record, but fails + as function <c>val/0</c> is undefined.</p> + + <pre> 35> <input>#rec{b = 3}.</input> -#rec{a = undefined,b = 3} +#rec{a = undefined,b = 3}</pre> + + <p>Command 35 shows the workaround: explicitly assign values to record + fields that cannot otherwise be initialized.</p> + + <pre> 36> <input>rp(v(-1)).</input> #rec{a = undefined,b = 3} -ok +ok</pre> + + <p>Command 36 prints the newly created record using record + definitions maintained by the shell.</p> + + <pre> 37> <input>rd(rec, {f = orddict:new()}).</input> -rec +rec</pre> + + <p>Command 37 defines a record directly in the shell. The + definition replaces the one read from file <c>ex.beam</c>.</p> + + <pre> 38> <input>#rec{}.</input> #rec{f = []} -ok +ok</pre> + + <p>Command 38 creates a record using the new definition, and + prints the result.</p> + + <pre> 39> <input>rd(rec, {c}), A.</input> -* 1: variable 'A' is unbound ** +* 1: variable 'A' is unbound 40> <input>#rec{}.</input> #rec{c = undefined} -ok +ok</pre> + + <p>Command 39 and 40 show that record definitions are updated + as side effects. The evaluation of the command fails, but + the definition of <c>rec</c> has been carried out.</p> + + <p>For the next command, it is assumed that <c>test1:loop(N)</c> is + defined as follows:</p> + + <p><c>loop(N) -></c><br></br> + <c>io:format("Hello Number: ~w~n", [N]),</c><br></br> + <c>loop(N+1).</c></p> + + <pre> 41> <input>test1:loop(0).</input> Hello Number: 0 Hello Number: 1 @@ -383,225 +551,122 @@ Hello Number: 3375 Hello Number: 3376 Hello Number: 3377 Hello Number: 3378 -** exception exit: killed +** exception exit: killed</pre> + + <p>Command 41 evaluates <c>test1:loop(0)</c>, which puts the + system into an infinite loop. At this point the user types + <c>^G</c> (Control G), which suspends output from the + current process, + which is stuck in a loop, and activates <c>JCL</c> mode. In <c>JCL</c> + mode the user can start and stop jobs.</p> + + <p>In this particular case, command <c>i</c> ("interrupt") + terminates the looping program, and command <c>c</c> + connects to the shell again. As the process was + running in the background before we killed it, more + printouts occur before message "<c>** exception exit: killed</c>" + is shown.</p> + + <pre> 42> <input>E = ets:new(t, []).</input> -17 +17</pre> + + <p>Command 42 creates an ETS table.</p> + + <pre> 43> <input>ets:insert({d,1,2}).</input> -** exception error: undefined function ets:insert/1 +** exception error: undefined function ets:insert/1</pre> + + <p>Command 43 tries to insert a tuple into the ETS table, but the + first argument (the table) is missing. The exception kills the + evaluator process.</p> + + <pre> 44> <input>ets:insert(E, {d,1,2}).</input> ** exception error: argument is of wrong type in function ets:insert/2 - called as ets:insert(16,{d,1,2}) + called as ets:insert(16,{d,1,2})</pre> + + <p>Command 44 corrects the mistake, but the ETS table has been + destroyed as it was owned by the killed evaluator process.</p> + + <pre> 45> <input>f(E).</input> ok 46> <input>catch_exception(true).</input> -false +false</pre> + + <p>Command 46 sets the exception handling of the evaluator process + to <c>true</c>. The exception handling can also be set when + starting Erlang by <c>erl -stdlib shell_catch_exception true</c>.</p> + + <pre> 47> <input>E = ets:new(t, []).</input> 18 48> <input>ets:insert({d,1,2}).</input> -* exception error: undefined function ets:insert/1 -49> <input>ets:insert(E, {d,1,2}).</input> -true -50> <input>halt().</input> -strider 2></pre> - </section> +* exception error: undefined function ets:insert/1</pre> - <section> - <title>Comments</title> - <p>Command 1 sets the variable <c>Str</c> to the string - <c>"abcd"</c>. - </p> - <p>Command 2 sets <c>L</c> to the length of the string evaluating - the BIF <c>atom_to_list</c>. - </p> - <p>Command 3 builds the tuple <c>Descriptor</c>. - </p> - <p>Command 4 prints the value of the variable <c>L</c>. - </p> - <p>Command 5 evaluates the internal shell command <c>b()</c>, which - is an abbreviation of "bindings". This prints - the current shell variables and their bindings. The <c>ok</c> at - the end is the return value of the <c>b()</c> function. - </p> - <p>Command 6 <c>f(L)</c> evaluates the internal shell command - <c>f(L)</c> (abbreviation of "forget"). The value of the variable - <c>L</c> is removed. - </p> - <p>Command 7 prints the new bindings. - </p> - <p>Command 8 has no effect since <c>L</c> has no value.</p> - <p>Command 9 performs a pattern matching operation on - <c>Descriptor</c>, binding a new value to <c>L</c>. - </p> - <p>Command 10 prints the current value of <c>L</c>. - </p> - <p>Command 11 tries to match <c>{P, Q, R}</c> against - <c>Descriptor</c> which is <c>{4, abc}</c>. The match fails and - none of the new variables become bound. The printout starting - with "<c>** exception error:</c>" is not the value of the - expression (the expression had no value because its evaluation - failed), but rather a warning printed by the system to inform - the user that an error has occurred. The values of the other - variables (<c>L</c>, <c>Str</c>, etc.) are unchanged. - </p> - <p>Commands 12 and 13 show that <c>P</c> is unbound because the - previous command failed, and that <c>Descriptor</c> has not - changed. - </p> - <p>Commands 14 and 15 show a correct match where <c>P</c> and - <c>Q</c> are bound. - </p> - <p>Command 16 clears all bindings. - </p> - <p>The next few commands assume that <c>test1:demo(X)</c> is - defined in the following way:</p> - <pre> -demo(X) -> - put(aa, worked), - X = 1, - X + 10. </pre> - <p>Commands 17 and 18 set and inspect the value of the item - <c>aa</c> in the process dictionary. - </p> - <p>Command 19 evaluates <c>test1:demo(1)</c>. The evaluation - succeeds and the changes made in the process dictionary become - visible to the shell. The new value of the dictionary item - <c>aa</c> can be seen in command 20. - </p> - <p>Commands 21 and 22 change the value of the dictionary item - <c>aa</c> to <c>hello</c> and call <c>test1:demo(2)</c>. Evaluation - fails and the changes made to the dictionary in - <c>test1:demo(2)</c>, before the error occurred, are discarded. - </p> - <p>Commands 23 and 24 show that <c>Z</c> was not bound and that the - dictionary item <c>aa</c> has retained its original value. - </p> - <p>Commands 25, 26 and 27 show the effect of evaluating - <c>test1:demo(1)</c> in the background. In this case, the - expression is evaluated in a newly spawned process. Any - changes made in the process dictionary are local to the newly - spawned process and therefore not visible to the shell. - </p> - <p>Commands 28, 29 and 30 use the history facilities of the shell. - </p> - <p>Command 29 is <c>e(28)</c>. This re-evaluates command - 28. Command 30 is <c>v(28)</c>. This uses the value (result) of - command 28. In the cases of a pure function (a function - with no side effects), the result is the same. For a function - with side effects, the result can be different. - </p> - <p>The next few commands show some record manipulation. It is - assumed that <c>ex.erl</c> defines a record like this:</p> - <pre> --record(rec, {a, b = val()}). - -val() -> - 3. </pre> - <p>Commands 31 and 32 compiles the file <c>ex.erl</c> and reads - the record definitions in <c>ex.beam</c>. If the compiler did not - output any record definitions on the BEAM file, <c>rr(ex)</c> - tries to read record definitions from the source file instead. - </p> - <p>Command 33 prints the definition of the record named - <c>rec</c>. - </p> - <p>Command 34 tries to create a <c>rec</c> record, but fails - since the function <c>val/0</c> is undefined. Command 35 shows - the workaround: explicitly assign values to record fields that - cannot otherwise be initialized. - </p> - <p>Command 36 prints the newly created record using record - definitions maintained by the shell. - </p> - <p>Command 37 defines a record directly in the shell. The - definition replaces the one read from the file <c>ex.beam</c>. - </p> - <p>Command 38 creates a record using the new definition, and - prints the result. - </p> - <p>Command 39 and 40 show that record definitions are updated - as side effects. The evaluation of the command fails but - the definition of <c>rec</c> has been carried out. - </p> - <p>For the next command, it is assumed that <c>test1:loop(N)</c> is - defined in the following way:</p> - <pre> -loop(N) -> - io:format("Hello Number: ~w~n", [N]), - loop(N+1).</pre> - <p>Command 41 evaluates <c>test1:loop(0)</c>, which puts the - system into an infinite loop. At this point the user types - <c>Control G</c>, which suspends output from the current process, - which is stuck in a loop, and activates <c>JCL</c> mode. In <c>JCL</c> - mode the user can start and stop jobs. - </p> - <p>In this particular case, the <c>i</c> command ("interrupt") is - used to terminate the looping program, and the <c>c</c> command - is used to connect to the shell again. Since the process was - running in the background before we killed it, there will be - more printouts before the "<c>** exception exit: killed</c>" - message is shown. - </p> - <p>Command 42 creates an ETS table.</p> - <p>Command 43 tries to insert a tuple into the ETS table but the - first argument (the table) is missing. The exception kills the - evaluator process.</p> - <p>Command 44 corrects the mistake, but the ETS table has been - destroyed since it was owned by the killed evaluator process.</p> - <p>Command 46 sets the exception handling of the evaluator process - to <c>true</c>. The exception handling can also be set when - starting Erlang, like this: <c>erl -stdlib shell_catch_exception - true</c>.</p> <p>Command 48 makes the same mistake as in command 43, but this time the evaluator process lives on. The single star at the beginning of the printout signals that the exception has been caught.</p> + + <pre> +49> <input>ets:insert(E, {d,1,2}).</input> +true</pre> + <p>Command 49 successfully inserts the tuple into the ETS table.</p> - <p>The <c>halt()</c> command exits the Erlang runtime system. - </p> + + <pre> +50> <input>halt().</input> +strider 2></pre> + + <p>Command 50 exits the Erlang runtime system.</p> </section> <section> <title>JCL Mode</title> <p>When the shell starts, it starts a single evaluator - process. This process, together with any local processes which + process. This process, together with any local processes that it spawns, is referred to as a <c>job</c>. Only the current job, which is said to be <c>connected</c>, can perform operations - with standard IO. All other jobs, which are said to be <c>detached</c>, are - <c>blocked</c> if they attempt to use standard IO. - </p> - <p>All jobs which do not use standard IO run in the normal way. - </p> - <p>The shell escape key <em><c>^G</c></em> (Control G) detaches the current job - and activates <c>JCL</c> mode. The <c>JCL</c> mode prompt is <c>"-->"</c>. If <c>"?"</c> is entered at the prompt, the following help message is - displayed:</p> - <pre> - --> ? - c [nn] - connect to job - i [nn] - interrupt job - k [nn] - kill job - j - list all jobs - s [shell] - start local shell - r [node [shell]] - start remote shell - q - quit erlang - ? | h - this message </pre> + with standard I/O. All other jobs, which are said to be <c>detached</c>, + are <c>blocked</c> if they attempt to use standard I/O.</p> + + <p>All jobs that do not use standard I/O run in the normal way.</p> + + <p>The shell escape key <c>^G</c> (Control G) detaches the current + job and activates <c>JCL</c> mode. The <c>JCL</c> mode prompt is + <c>"-->"</c>. If <c>"?"</c> is entered at the prompt, the following help + message is displayed:</p> + + <pre> +--> ? +c [nn] - connect to job +i [nn] - interrupt job +k [nn] - kill job +j - list all jobs +s [shell] - start local shell +r [node [shell]] - start remote shell +q - quit erlang +? | h - this message</pre> + <p>The <c>JCL</c> commands have the following meaning:</p> + <taglist> <tag><c>c [nn]</c></tag> <item> <p>Connects to job number <c><![CDATA[<nn>]]></c> or the current - job. The standard shell is resumed. Operations which use - standard IO by the current job will be interleaved with - user inputs to the shell. - </p> + job. The standard shell is resumed. Operations that use + standard I/O by the current job are interleaved with + user inputs to the shell.</p> </item> <tag><c>i [nn]</c></tag> <item> <p>Stops the current evaluator process for job number <c>nn</c> or the current job, but does not kill the shell - process. Accordingly, any variable bindings and the process dictionary - will be preserved and the job can be connected again. - This command can be used to interrupt an endless loop. - </p> + process. So, any variable bindings and the process + dictionary are preserved and the job can be connected again. + This command can be used to interrupt an endless loop.</p> </item> <tag><c>k [nn]</c></tag> <item> @@ -609,135 +674,166 @@ loop(N) -> job. All spawned processes in the job are killed, provided they have not evaluated the <c>group_leader/1</c> BIF and are located on - the local machine. Processes spawned on remote nodes will - not be killed. - </p> + the local machine. Processes spawned on remote nodes + are not killed.</p> </item> <tag><c>j</c></tag> <item> <p>Lists all jobs. A list of all known jobs is - printed. The current job name is prefixed with '*'. - </p> + printed. The current job name is prefixed with '*'.</p> </item> <tag><c>s</c></tag> <item> - <p>Starts a new job. This will be assigned the new index - <c>[nn]</c> which can be used in references. - </p> + <p>Starts a new job. This is assigned the new index + <c>[nn]</c>, which can be used in references.</p> </item> <tag><c>s [shell]</c></tag> <item> - <p>Starts a new job. This will be assigned the new index - <c>[nn]</c> which can be used in references. - If the optional argument <c>shell</c> is given, it is assumed - to be a module that implements an alternative shell. - </p> + <p>Starts a new job. This is assigned the new index + <c>[nn]</c>, which can be used in references. + If optional argument <c>shell</c> is specified, it is assumed + to be a module that implements an alternative shell.</p> </item> <tag><c>r [node]</c></tag> <item> <p>Starts a remote job on <c>node</c>. This is used in distributed Erlang to allow a shell running on one node to - control a number of applications running on a network of - nodes. - If the optional argument <c>shell</c> is given, it is assumed - to be a module that implements an alternative shell. - </p> + control a number of applications running on a network of nodes. + If optional argument <c>shell</c> is specified, it is assumed + to be a module that implements an alternative shell.</p> </item> <tag><c>q</c></tag> <item> - <p>Quits Erlang. Note that this option is disabled if - Erlang is started with the ignore break, <c>+Bi</c>, - system flag (which may be useful e.g. when running - a restricted shell, see below). - </p> + <p>Quits Erlang. Notice that this option is disabled if + Erlang is started with the ignore break, <c>+Bi</c>, + system flag (which can be useful, for example when running + a restricted shell, see the next section).</p> </item> <tag><c>?</c></tag> <item> - <p>Displays this message.</p> + <p>Displays the help message above.</p> </item> </taglist> - <p>It is possible to alter the behavior of shell escape by means - of the STDLIB application variable <c>shell_esc</c>. The value of + + <p>The behavior of shell escape can be changed by the STDLIB + application variable <c>shell_esc</c>. The value of the variable can be either <c>jcl</c> (<c>erl -stdlib shell_esc jcl</c>) or <c>abort</c> (<c>erl -stdlib shell_esc abort</c>). The - first option sets ^G to activate <c>JCL</c> mode (which is also - default behavior). The latter sets ^G to terminate the current - shell and start a new one. <c>JCL</c> mode cannot be invoked when - <c>shell_esc</c> is set to <c>abort</c>. </p> - <p>If you want an Erlang node to have a remote job active from the start - (rather than the default local job), you start Erlang with the - <c>-remsh</c> flag. Example: <c>erl -sname this_node -remsh other_node@other_host</c></p> + first option sets <c>^G</c> to activate <c>JCL</c> mode (which + is also default behavior). The latter sets <c>^G</c> to + terminate the current shell and start a new one. + <c>JCL</c> mode cannot be invoked when + <c>shell_esc</c> is set to <c>abort</c>.</p> + + <p>If you want an Erlang node to have a remote job active from the start + (rather than the default local job), start Erlang with flag + <c>-remsh</c>, for example, + <c>erl -sname this_node -remsh other_node@other_host</c></p> </section> <section> <title>Restricted Shell</title> - <p>The shell may be started in a + <p>The shell can be started in a restricted mode. In this mode, the shell evaluates a function call only if allowed. This feature makes it possible to, for example, prevent a user from accidentally calling a function from the prompt that could harm a running system (useful in combination - with the the system flag <em><c>+Bi</c></em>).</p> + with system flag <c>+Bi</c>).</p> + <p>When the restricted shell evaluates an expression and - encounters a function call or an operator application, + encounters a function call or an operator application, it calls a callback function (with information about the function call in question). This callback function returns <c>true</c> to let the shell go ahead with the evaluation, or <c>false</c> to abort it. There are two possible callback functions for the user to implement:</p> - <p><em><c>local_allowed(Func, ArgList, State) -> {true,NewState} | {false,NewState}</c></em></p> - <p>to determine if the call to the local function <c>Func</c> - with arguments <c>ArgList</c> should be allowed.</p> - <p><em><c>non_local_allowed(FuncSpec, ArgList, State) -> {true,NewState} | {false,NewState} | {{redirect,NewFuncSpec,NewArgList},NewState}</c></em></p> - <p>to determine if the call to non-local function - <c>FuncSpec</c> (<c>{Module,Func}</c> or a fun) with arguments - <c>ArgList</c> should be allowed. The return value - <c>{redirect,NewFuncSpec,NewArgList}</c> can be used to let - the shell evaluate some other function than the one specified by - <c>FuncSpec</c> and <c>ArgList</c>.</p> - <p>These callback functions are in fact called from local and + + <list type="bulleted"> + <item> + <p><c>local_allowed(Func, ArgList, State) -> {boolean(),NewState}</c></p> + <p>This is used to determine if the call to the local function + <c>Func</c> with arguments <c>ArgList</c> is to be allowed.</p> + </item> + <item> + <p><c>non_local_allowed(FuncSpec, ArgList, State) + -> {boolean(),NewState} + | {{redirect,NewFuncSpec,NewArgList},NewState}</c></p> + <p>This is used to determine if the call to non-local function + <c>FuncSpec</c> (<c>{Module,Func}</c> or a fun) with arguments + <c>ArgList</c> is to be allowed. The return value + <c>{redirect,NewFuncSpec,NewArgList}</c> can be used to let + the shell evaluate some other function than the one specified by + <c>FuncSpec</c> and <c>ArgList</c>.</p> + </item> + </list> + + <p>These callback functions are called from local and non-local evaluation function handlers, described in the - <seealso marker="erl_eval">erl_eval</seealso> + <seealso marker="erl_eval"><c>erl_eval</c></seealso> manual page. (Arguments in <c>ArgList</c> are evaluated before the callback functions are called.)</p> - <p>The <c>State</c> argument is a tuple + + <p>Argument <c>State</c> is a tuple <c>{ShellState,ExprState}</c>. The return value <c>NewState</c> - has the same form. This may be used to carry a state between calls + has the same form. This can be used to carry a state between calls to the callback functions. Data saved in <c>ShellState</c> lives through an entire shell session. Data saved in <c>ExprState</c> lives only through the evaluation of the current expression.</p> + <p>There are two ways to start a restricted shell session:</p> + <list type="bulleted"> - <item>Use the STDLIB application variable <c>restricted_shell</c> - and specify, as its value, the name of the callback - module. Example (with callback functions implemented in - callback_mod.erl): <c>$ erl -stdlib restricted_shell callback_mod</c></item> - <item>From a normal shell session, call function - <c>shell:start_restricted/1</c>. This exits the current evaluator - and starts a new one in restricted mode.</item> + <item> + <p>Use STDLIB application variable <c>restricted_shell</c> + and specify, as its value, the name of the callback + module. Example (with callback functions implemented in + <c>callback_mod.erl</c>): + <c>$ erl -stdlib restricted_shell callback_mod</c>.</p> + </item> + <item> + <p>From a normal shell session, call function + <seealso marker="#start_restricted/1"> + <c>start_restricted/1</c></seealso>. This exits the current evaluator + and starts a new one in restricted mode.</p> + </item> </list> + <p><em>Notes:</em></p> <list type="bulleted"> - <item>When restricted shell mode is activated or - deactivated, new jobs started on the node will run in restricted - or normal mode respectively.</item> - <item>If restricted mode has been enabled on a - particular node, remote shells connecting to this node will also - run in restricted mode.</item> - <item>The callback functions cannot be used to allow or disallow - execution of functions called from compiled code (only functions - called from expressions entered at the shell prompt).</item> + <item> + <p>When restricted shell mode is activated or + deactivated, new jobs started on the node run in restricted + or normal mode, respectively.</p> + </item> + <item> + <p>If restricted mode has been enabled on a + particular node, remote shells connecting to this node also + run in restricted mode.</p> + </item> + <item> + <p>The callback functions cannot be used to allow or disallow + execution of functions called from compiled code (only functions + called from expressions entered at the shell prompt).</p> + </item> </list> + <p>Errors when loading the callback module is handled in different ways depending on how the restricted shell is activated:</p> + <list type="bulleted"> - <item>If the restricted shell is activated by setting the kernel - variable during emulator startup and the callback module cannot be - loaded, a default restricted shell allowing only the commands - <c>q()</c> and <c>init:stop()</c> is used as fallback.</item> - <item>If the restricted shell is activated using - <c>shell:start_restricted/1</c> and the callback module cannot be - loaded, an error report is sent to the error logger and the call - returns <c>{error,Reason}</c>.</item> + <item> + <p>If the restricted shell is activated by setting the STDLIB + variable during emulator startup, and the callback module cannot be + loaded, a default restricted shell allowing only the commands + <c>q()</c> and <c>init:stop()</c> is used as fallback.</p> + </item> + <item> + <p>If the restricted shell is activated using + <seealso marker="#start_restricted/1"> + <c>start_restricted/1</c></seealso> and the callback module cannot + be loaded, an error report is sent to the error logger and the call + returns <c>{error,Reason}</c>.</p> + </item> </list> </section> @@ -746,44 +842,27 @@ loop(N) -> <p>The default shell prompt function displays the name of the node (if the node can be part of a distributed system) and the current command number. The user can customize the prompt - function by calling - <c>shell:prompt_func/1</c> or by setting the application + function by calling <seealso marker="#prompt_func/1"> + <c>prompt_func/1</c></seealso> or by setting application configuration parameter <c>shell_prompt_func</c> for the - application STDLIB.</p> + STDLIB application.</p> + <p>A customized prompt function is stated as a tuple <c>{Mod, Func}</c>. The function is called as <c>Mod:Func(L)</c>, where <c>L</c> is a list of key-value pairs created by the shell. Currently there is only one pair: - <c>{history, N}</c>, where N is the current command number. The - function should return a list of characters or an atom. This - constraint is due to the Erlang I/O-protocol. Unicode characters - beyond codepoint 255 are allowed in the list. Note + <c>{history, N}</c>, where <c>N</c> is the current command number. The + function is to return a list of characters or an atom. This + constraint is because of the Erlang I/O protocol. Unicode characters + beyond code point 255 are allowed in the list. Notice that in restricted mode the call <c>Mod:Func(L)</c> must be - allowed or the default shell prompt function will be called.</p> - </section> + allowed or the default shell prompt function is called.</p> + </section> <funcs> <func> - <name name="history" arity="1"/> - <fsummary>Sets the number of previous commands to keep</fsummary> - <desc> - <p>Sets the number of previous commands to keep in the - history list to <c><anno>N</anno></c>. The previous number is returned. - The default number is 20.</p> - </desc> - </func> - <func> - <name name="results" arity="1"/> - <fsummary>Sets the number of previous results to keep</fsummary> - <desc> - <p>Sets the number of results from previous commands to keep in - the history list to <c><anno>N</anno></c>. The previous number is returned. - The default number is 20.</p> - </desc> - </func> - <func> <name>catch_exception(Bool) -> boolean()</name> - <fsummary>Sets the exception handling of the shell</fsummary> + <fsummary>Set the exception handling of the shell.</fsummary> <type> <v>Bool = boolean()</v> </type> @@ -793,52 +872,76 @@ loop(N) -> (<c>false</c>) is to kill the evaluator process when an exception occurs, which causes the shell to create a new evaluator process. When the exception handling is set to - <c>true</c> the evaluator process lives on which means that - for instance ports and ETS tables as well as processes + <c>true</c>, the evaluator process lives on, which means that, + for example, ports and ETS tables as well as processes linked to the evaluator process survive the exception.</p> </desc> </func> + + <func> + <name name="history" arity="1"/> + <fsummary>Set the number of previous commands to keep.</fsummary> + <desc> + <p>Sets the number of previous commands to keep in the + history list to <c><anno>N</anno></c>. The previous number is + returned. Defaults to 20.</p> + </desc> + </func> + <func> <name name="prompt_func" arity="1"/> - <fsummary>Sets the shell prompt</fsummary> + <fsummary>Set the shell prompt.</fsummary> <desc> <p>Sets the shell prompt function to <c><anno>PromptFunc</anno></c>. The previous prompt function is returned.</p> </desc> </func> + + <func> + <name name="results" arity="1"/> + <fsummary>Set the number of previous results to keep.</fsummary> + <desc> + <p>Sets the number of results from previous commands to keep in + the history list to <c><anno>N</anno></c>. The previous number is + returned. Defaults to 20.</p> + </desc> + </func> + <func> <name name="start_restricted" arity="1"/> - <fsummary>Exits a normal shell and starts a restricted shell.</fsummary> + <fsummary>Exit a normal shell and starts a restricted shell.</fsummary> <desc> - <p>Exits a normal shell and starts a restricted - shell. <c><anno>Module</anno></c> specifies the callback module for the + <p>Exits a normal shell and starts a restricted shell. + <c><anno>Module</anno></c> specifies the callback module for the functions <c>local_allowed/3</c> and <c>non_local_allowed/3</c>. The function is meant to be called from the shell.</p> <p>If the callback module cannot be loaded, an error tuple is returned. The <c><anno>Reason</anno></c> in the error tuple is the one - returned by the code loader when trying to load the code of the callback - module.</p> + returned by the code loader when trying to load the code of the + callback module.</p> </desc> </func> + <func> <name name="stop_restricted" arity="0"/> - <fsummary>Exits a restricted shell and starts a normal shell.</fsummary> + <fsummary>Exit a restricted shell and starts a normal shell.</fsummary> <desc> <p>Exits a restricted shell and starts a normal shell. The function is meant to be called from the shell.</p> </desc> </func> + <func> <name name="strings" arity="1"/> - <fsummary>Sets the shell's string recognition flag.</fsummary> + <fsummary>Set the shell's string recognition flag.</fsummary> <desc> <p>Sets pretty printing of lists to <c><anno>Strings</anno></c>. The previous value of the flag is returned.</p> <p>The flag can also be set by the STDLIB application variable - <c>shell_strings</c>. The default is - <c>true</c> which means that lists of integers will be - printed using the string syntax, when possible. The value - <c>false</c> means that no lists will be printed using the + <c>shell_strings</c>. Defaults to + <c>true</c>, which means that lists of integers are + printed using the string syntax, when possible. Value + <c>false</c> means that no lists are printed using the string syntax.</p> </desc> </func> |