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--- syntax:basicgrammar [2011/01/02 09:42]
thebonsai fixes and lastpipe option
+++ syntax:basicgrammar [2015/08/10 03:37]
bill_thomson
@@ Line 3: / Line 3: @@
 {{keywords>bash shell scripting grammar syntax language}}
-Bash builds its features on top of a few basic **grammar rules**. The code you see everywhere, the code you use, is based on these rules. However, **this is a very theoretical view**, but if you're interested, it may help you to understand why things look like they look.
+Bash builds its features on top of a few basic **grammar rules**. The code you see everywhere, the code you use, is based on those rules. However, **this is a very theoretical view**, but if you're interested, it may help you understand why things look the way they look.
-In the following examples, some commands will be used. If you don't know these commands, just believe the short explanation. Here, they are only used as examples.
+If you don't know the commands used in the following examples, just trust the explanation.
 ===== Simple Commands =====
@@ Line 13: / Line 12: @@
 A simple command is a sequence of optional variable assignments followed by blank-separated words and redirections,
 and terminated by a control operator. The first word specifies the command to be executed, and is passed as argument
-zero.  The remaining words are passed as  arguments to the invoked command.
+zero.  The remaining words are passed as arguments to the invoked command.
 </code>
-Sounds harder than it actually is. It is what you do day-per-day. You enter simple commands with parameters and the shell executes them.
+Sounds harder than it actually is. It is what you do daily. You enter simple commands with parameters, and the shell executes them.
-Every more complex operation in Bash can be finally splitted into executing such simple commands:
+Every complex Bash operationcan be split into simple commands:
 <code>
 ls
@@ Line 26: / Line 25: @@
 </code>
-The last one might not be familiar to you. That one simply adds "''LC_ALL=C''" to the environment of the ''ls''-program. It doesn't affect your current shell. This also works while calling functions, unless Bash runs in POSIX(r) mode (then it affects your current shell).
+The last one might not be familiar. That one simply adds "''LC_ALL=C''" to the environment of the ''ls'' program. It doesn't affect your current shell. This also works while calling functions, unless Bash runs in POSIX(r) mode (in which case it affects your current shell).
-Every command has a so-called exit code - it's a kind of return status. The shell can catch it and react on it. It goes from 0 to 255, where 0 means success, and the rest means any kind of failure or issue to report back to the caller.
+Every command has an exit code. It's a type of return status. The shell can catch it and act on it. Exit code range is from 0 to 255, where 0 means success, and the rest mean either something failed, or there is an issue to report back to the calling program.
 <wrap center round info 90%>
-The simple command construct is the **base** for all higher constructs. Everything you execute, form pipelines to functions, finally ends up in (many) simple commands. That's why Bash only has one method to [[syntax:grammar:parser_exec | finally expand and execute a simple command]].
+The simple command construct is the **base** for all higher constructs. Everything you execute, from pipelines to functions, finally ends up in (many) simple commands. That's why Bash only has one method to [[syntax:grammar:parser_exec | expand and execute a simple command]].
 </wrap>
 ===== Pipelines =====
-FIXME Missing an additional extra article about pipelines and pipelining
+FIXME Missing an additional article about pipelines and pipelining
 ''[time [-p]] [ ! ] command [ | command2 ... ]''
-**Don't get confused** about the name "pipeline" here, it's a grammar name for that construct, such a pipeline isn't necessarily a pair of commands where stdout/stdin is connected through a real pipe.
+**Don't get confused** about the name "pipeline." It's a grammatic name for a construct. Such a pipeline isn't necessarily a pair of commands where stdout/stdin is connected via a real pipe.
-Basically, pipelines are one or more [[basicgrammar##simple_commands | simple commands]] (when more, separated by the ''|''-symbol and connecting their input and output), for example:
+Pipelines are one or more [[basicgrammar##simple_commands | simple commands]] (separated by the ''|'' symbol connects their input and output), for example:
 <code>ls /etc | wc -l</code>
-will execute ''ls'' on ''/etc'' and **pipe** the output to ''wc'', which will count lines. That way, you simply count your directory entries in /etc.
+will execute ''ls'' on ''/etc'' and **pipe** the output to ''wc'', which will count the lines generated by the ls command. The result is the number of directory entries in /etc.
-The last command in the pipeline will also set the exit code for the pipeline. This exit code can be "reversed" by preceeding an exclamation-mark to the pipeline: An unsuccessful pipeline will end up "successful" and vice versa.
+The last command in the pipeline will set the exit code for the pipeline. This exit code can be "inverted" by prefixing an exclamation mark to the pipeline: An unsuccessful pipeline will exit "successful" and vice versa.
-In this example, the commands in the if-structure will be executed, if the pattern "^root:" is **not** found in ''/etc/passwd'':
+In this example, the commands in the if stanza will be executed if the pattern "^root:" is **not** found in ''/etc/passwd'':
 <code>
 if ! grep '^root:' /etc/passwd; then
-  echo "No root-user defined... eh?"
+  echo "No root user defined... eh?"
 fi
 </code>
-Yes, this is also a pipeline (though there is no piping!), because the **exclamation mark to reverse the exit code** can only be used in pipelines.
+Yes, this is also a pipeline (although there is no pipe!), because the **exclamation mark to invert the exit code** can only be used in a pipeline.
-If ''grep'''s exit code is 1 (FALSE) (the text was not found), the leading ''!'' will "reverse" the exit code for the shell, the shell sees (and reacts on) exit code 0 (TRUE) and the ''then''-path of the ''if''-clause is executed. One could say we checked for "''not grep "^root" /etc/passwd''".
+If ''grep'''s exit code is 1 (FALSE) (the text was not found), the leading ''!'' will "invert" the exit code, and the shell sees (and acts on) exit code 0 (TRUE) and the ''then'' part of the ''if'' stanza is executed. One could say we checked for "''not grep "^root" /etc/passwd''".
-The [[commands:builtin:set#attributes | set option pipefail]] determines the behavior of how bash reports exit code of pipeline. If it's set, then the exit code (''$?'') is the last command that exits with non-0 status, if none fails, it's 0. If it's not set, then ''$?'' always holds the exit code of the last command (as explained above).
+The [[commands:builtin:set#attributes | set option pipefail]] determines the behavior of how bash reports the exit code of a pipeline. If it's set, then the exit code (''$?'') is the last command that exits with non zero status, if none fail, it's zero. If it's not set, then ''$?'' always holds the exit code of the last command (as explained above).
-The shell option ''[[internals:shell_options#lastpipe | lastpipe]]'' will make the last element in a pipeline construct being executed in the current shell environment, not in a separate subshell.
+The shell option ''[[internals:shell_options#lastpipe | lastpipe]]'' will execute the last element in a pipeline construct in the current shell environment, i.e. not a subshell.
-There's also an array ''PIPESTATUS[]'' that is set after a foreground pipeline is executed. Each element of ''PIPESTATUS[]'' reports the exit code of each respective command in the pipeline. Note: (1) it's only for foreground pipe and (2) for higher level structure that is built up from pipeline, like list, ''PIPESTATUS[]'' holds only the last pipeline executed.
+There's also an array ''PIPESTATUS[]'' that is set after a foreground pipeline is executed. Each element of ''PIPESTATUS[]'' reports the exit code of the respective command in the pipeline. Note: (1) it's only for foreground pipe and (2) for higher level structure that is built up from a pipeline. Like list, ''PIPESTATUS[]'' holds the exit status of the last pipeline command executed.
-Another thing you can do with pipelines is logging their execution time. Note that **''time'' is not a command**, it belongs to the special words for pipeline-syntax:
+Another thing you can do with pipelines is log their execution time. Note that **''time'' is not a command**, it is part of the pipeline syntax:
 <code>
 # time updatedb
@@ Line 72: / Line 71: @@
 ===== Lists =====
-FIXME Missing an additional extra article about the list operators
+FIXME Missing an additional article about list operators
 A list is a sequence of one or more [[basicgrammar#pipelines | pipelines]] separated by one of the operators '';'', ''&'', ''&&'', or ''││'', and optionally terminated by one of '';'', ''&'', or ''<newline>''.
-=> It's a bunch of **pipelines** separated or terminated by **tokens** that all have **different meanings** for Bash.
+=> It's a group of **pipelines** separated or terminated by **tokens** that all have **different meanings** for Bash.
 Your whole Bash script technically is one big single list!
 ^Operator^Description^
-|''<PIPELINE1> **<newline>** <PIPELINE2>''|Newlines completely separate pipelines. The next pipeline is simply executed, without any checks or specials (Hey! You do that every day! You enter a command and press ''<RETURN>''!)|
+|''<PIPELINE1> **<newline>** <PIPELINE2>''|Newlines completely separate pipelines. The next pipeline is executed without any checks. You enter a command and press ''<RETURN>''!)|
-|''<PIPELINE1> **;** <PIPELINE2>''|The semicolon does what ''<newline>'' does: It completely separates the pipelines|
+|''<PIPELINE1> **;** <PIPELINE2>''|The semicolon does what ''<newline>'' does: It separates the pipelines|
-|''<PIPELINE> **&** <PIPELINE>''|The pipeline infront of that ''&'' is executed **async** ("in background") - if a pipeline follows this, it is immediately executed after the async one was started|
+|''<PIPELINE> **&** <PIPELINE>''|The pipeline in front of the ''&'' is executed **asynchronously** ("in the background"). If a pipeline follows this, it is executed immediately after the async pipeline starts|
 |''<PIPELINE1> **&&** <PIPELINE2>''|''<PIPELINE1>'' is executed and **only** if its exit code was 0 (TRUE), then ''<PIPELINE2>'' is executed (AND-List)|
 |''<PIPELINE1> **<nowiki>||</nowiki>** <PIPELINE2>''|''<PIPELINE1>'' is executed and **only** if its exit code was **not** 0 (FALSE), then ''<PIPELINE2>'' is executed (OR-List)|
@@ Line 94: / Line 93: @@
 There are two forms of compound commands:
-  * forming a new syntax element using lists as "body"
+  * form a new syntax element using a list as a "body"
-  * complete independant syntax elements
+  * completly independant syntax elements
-Basically, it's everything else that's not described elsewhere in this article. Compound commands have the following characteristics:
+Essentially, everything else that's not described in this article. Compound commands have the following characteristics:
   * they **begin** and **end** with a specific keyword or operator (e.g. ''for ... done'')
   * they can be redirected as a whole
-See the following table for a short overview (without details - really just a plain overview!):
+See the following table for a short overview (no details - just an overview):
 ^Compound command syntax^Description^
 |''( <LIST> )''|Execute ''<LIST>'' in an extra subshell => [[syntax:ccmd:grouping_subshell | article]]|
@@ Line 108: / Line 107: @@
 |''for <NAME> in <WORDS> ; do <LIST> ; done''|Executes ''<LIST>'' while setting the variable ''<NAME>'' to one of ''<WORDS>'' on every iteration (classic for-loop) => [[syntax:ccmd:classic_for | article]]|
 |''for <nowiki>((</nowiki> <EXPR1> ; <EXPR2> ; <EXPR3> )) ; do <LIST> ; done''|C-style for-loop (driven by arithmetic expressions) => [[syntax:ccmd:c_for | article]]|
-|''select <NAME> in <WORDS> ; do <LIST> ; done''|Providing simple menus => [[syntax:ccmd:user_select | article]]|
+|''select <NAME> in <WORDS> ; do <LIST> ; done''|Provides simple menus => [[syntax:ccmd:user_select | article]]|
-|''case <WORD> in <PATTERN>) <LIST> ;; ... esac''|Decicions based on pattern matching - executing ''<LIST>'' on match => [[syntax:ccmd:case | article]]|
+|''case <WORD> in <PATTERN>) <LIST> ;; ... esac''|Decisions based on pattern matching - executing ''<LIST>'' on match => [[syntax:ccmd:case | article]]|
-|''if <LIST> ; then <LIST> ; else <LIST> ; fi''|The if-clause: making decisions based on exit codes => [[syntax:ccmd:if_clause | article]]|
+|''if <LIST> ; then <LIST> ; else <LIST> ; fi''|The if clause: makes decisions based on exit codes => [[syntax:ccmd:if_clause | article]]|
 |''while <LIST1> ; do <LIST2> ; done''|Execute ''<LIST2>'' while ''<LIST1>'' returns TRUE (exit code) => [[syntax:ccmd:while_loop | article]]|
 |''until <LIST1> ; do <LIST2> ; done''|Execute ''<LIST2>'' until ''<LIST1>'' returns TRUE (exit code) => [[syntax:ccmd:until_loop | article]]|
@@ Line 118: / Line 117: @@
 ===== Shell Function Definitions =====
-FIXME Missing an additional extra article about shell functions
+FIXME Missing an additional article about shell functions
-A shell function definition basically makes a [[basicgrammar#compound_commands | compound command]] available under a new name. The speciality now is, that function, when ran, has its own "private" set of positional parameters and I/O descriptors. It acts like a script in the script. Simple said: **You create a new command.**
+A shell function definition makes a [[basicgrammar#compound_commands | compound command]] available via a new name. When the function runs, it has its own "private" set of positional parameters and I/O descriptors. It acts like a script-within-the-script. Simply stated: **You've created a new command.**
-The definition is easy (one of more possibilities):
+The definition is easy (one of many possibilities):
 ''<NAME> () <COMPOUND_COMMAND> <REDIRECTIONS>''
-which usually is used with the ''{...; }'' compound command, and thus looks like
+which is usually used with the ''{...; }'' compound command, and thus looks like:
 <code>
 print_help() { echo "Sorry, no help available"; }
 </code>
-Like told above, a function definition can have any [[basicgrammar#compound_commands | compound command]] as body. Structures like
+As above, a function definition can have any [[basicgrammar#compound_commands | compound command]] as a body. Structures like
 <code>
 countme() for ((x=1;x<=9;x++)); do echo $x; done
 </code>
-are unusual, but perfectly valid since the for-loop construct is a compound command!
+are unusual, but perfectly valid, since the for loop construct is a compound command!
-If there are **redirections** specified, these are not performed on function definition, they are performed on function execution:
+If **redirection** is specified, the redirection is not performed when the function is defined. It is performed when the function runs:
 <code>
-# this will NOT perform the redirection (on definition time)
+# this will NOT perform the redirection (at definition time)
 f() { echo ok ; } > file
@@ Line 153: / Line 152: @@
 </code>
-The space between ''NAME'' and ''()'' is optional, usually you just see it without.
+The space between ''NAME'' and ''()'' is optional, usually you see it without the space.
-I suggest to use the first form. It's specified in POSIX and all Bourne-like shells seem to support it.
+I suggest using the first form. It's specified in POSIX and all Bourne-like shells seem to support it.
-__**Note:**__ Before version ''2.05-alpha1'', Bash only recognized the definition using curly braces (''name() { ... }''), also, other shells allow the definition using **any** command (not only compound command set).
+__**Note:**__ Before version ''2.05-alpha1'', Bash only recognized the definition using curly braces (''name() { ... }''), other shells allow the definition using **any** command (not just the compound command set).
-To execute a funtion like a regular shell script you would put it together like this:
+To execute a function like a regular shell script you put it together like this:
 <code>
@@ Line 167: / Line 166: @@
 mycmd()
 {
-  # this $1 is the one of the function!
+  # this $1 belongs to the function!
   find / -iname "$1"
 }
-# this $1 is the one of the script itself!
+# this $1 belongs the script itself!
 mycmd "$1" # Execute command immediately after defining function
@@ Line 179: / Line 178: @@
 **Just informational(1):**
-Internally, for forking, Bash stores the function definitions in environment variables. Variables with the content "//() ....//".
+Internally, for forking, Bash stores function definitions in environment variables. Variables with the content "//() ....//".
-Something like the following works without "officially" declaring a function:
+Something similar to the following works without "officially" declaring a function:
 <code>
 $ export testfn="() { echo test; }"
@@ Line 191: / Line 190: @@
 **Just informational(2):**
-It is possible to set function names containing slashes:
+It is possible to create function names containing slashes:
 <code>
@@ Line 199: / Line 198: @@
 </code>
-The elements of this name aren't subject to path search, of course.
+The elements of this name aren't subject to a path search.
+Weird function names should not be used. Quote from the maintainer:
+  * //
+It was a mistake to allow such characters in function names (`unset' doesn't
+work to unset them without forcing -f, for instance).  We're stuck with them
+for backwards compatibility, but I don't have to encourage their use.
+//
 ===== Grammar summary =====
-Not much of correct definitions, just some short **slogans**:
   * a [[basicgrammar#simple_commands | simple command]] is just a command and its arguments
   * a [[basicgrammar#pipelines | pipeline]] is one or more [[basicgrammar#simple_commands | simple command]] probably connected in a pipe
   * a [[basicgrammar#lists | list]] is one or more [[basicgrammar#pipelines | pipelines]] connected by special operators
   * a [[basicgrammar#compound_commands | compound command]] is a [[basicgrammar#lists | list]] or a special command that forms a new meta-command
-  * a [[basicgrammar#shell_function_definitions | function definition]] makes a [[basicgrammar#compound_commands | compound command]] available under a new name, and in some kind of separate environment
+  * a [[basicgrammar#shell_function_definitions | function definition]] makes a [[basicgrammar#compound_commands | compound command]] available under a new name, and a separate environment
@@ Line 215: / Line 221: @@
 ----
-__A (very ;-)) simple command__
+__A (very) simple command__
 <code>
 echo "Hello world..."
 </code>
+__All of the following are simple commands__
+<code>x=5</code>
+<code>>tmpfile</code>
+<code>{x}<"$x" _=${x=<(echo moo)} <&0$(cat <&"$x" >&2)</code>
 ----
 __A common compound command__
@@ Line 226: / Line 237: @@
 fi
 </code>
-  * the [[basicgrammar#compound_commands | compound command]] for the ''if''-clause
+  * the [[basicgrammar#compound_commands | compound command]] for the ''if'' clause
   * the [[basicgrammar#lists | list]] that ''if'' **checks** actually contains the [[basicgrammar#simple_commands | simple command]] ''[ -d /data/mp3 ]''
   * the [[basicgrammar#lists | list]] that ''if'' **executes** contains a simple command (''cp mymusic.mp3 /data/mp3'')
-Let's reverse the exit code of the test command, only one thing changes:
+Let's invert test command exit code, only one thing changes:
 <code>
 if ! [ -d /data/mp3 ]; then
@@ Line 238: / Line 249: @@
 </code>
   * the [[basicgrammar#lists | list]] that ''if'' **checks** contains a [[basicgrammar#pipelines | pipeline]] now (because of the ''!'')