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Chet Ramey
2011-12-12 21:59:37 -05:00
parent eb0b2ad86b
commit 6faad6254a
160 changed files with 12731 additions and 588 deletions
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doc/bashref.texi
+143 -12
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@@ -596,6 +596,7 @@ some other grouping.
* Lists:: How to execute commands sequentially.
* Compound Commands:: Shell commands for control flow.
* Coprocesses:: Two-way communication between commands.
* GNU Parallel:: Running commands in parallel.
@end menu
@node Simple Commands
@@ -654,6 +655,12 @@ The use of @code{time} as a reserved word permits the timing of
shell builtins, shell functions, and pipelines. An external
@code{time} command cannot time these easily.
When the shell is in @sc{posix} mode (@pxref{Bash POSIX Mode}), @code{time}
may be followed by a newline. In this case, the shell displays the
total user and system time consumed by the shell and its children.
The @env{TIMEFORMAT} variable may be used to specify the format of
the time information.
If the pipeline is not executed asynchronously (@pxref{Lists}), the
shell waits for all commands in the pipeline to complete.
@@ -1132,6 +1139,79 @@ builtin command may be used to wait for the coprocess to terminate.
The return status of a coprocess is the exit status of @var{command}.
@node GNU Parallel
@subsection GNU Parallel
GNU Parallel, as its name suggests, can be used to build and run commands
in parallel. You may run the same command with different arguments, whether
they are filenames, usernames, hostnames, or lines read from files.
For a complete description, refer to the GNU Parallel documentation. A few
examples should provide a brief introduction to its use.
For example, it is easy to prefix each line in a text file with a specified
string:
@example
cat file | parallel -k echo prefix_string
@end example
The @option{-k} option is required to preserve the lines' order.
Similarly, you can append a specified string to each line in a text file:
@example
cat file | parallel -k echo @{@} append_string
@end example
You can use Parallel to move files from the current directory when the
number of files is too large to process with one @code{mv} invocation:
@example
ls | parallel mv @{@} destdir
@end example
As you can see, the @{@} is replaced with each line read from standard input.
This will run as many @code{mv} commands as there are files in the current
directory. You can emulate a parallel @code{xargs} by adding the @option{-X}
option:
@example
ls | parallel -X mv @{@} destdir
@end example
GNU Parallel can replace certain common idioms that operate on lines read
from a file (in this case, filenames):
@example
for x in $(cat list); do
do-something1 $x config-$x
do-something2 < $x
done | process-output
@end example
with a more compact syntax reminiscent of lambdas:
@example
cat list | parallel "do-something1 @{@} config-@{@} ; do-something2 < @{@}" | process-output
@end example
Parallel provides a built-in mechanism to remove filename extensions, which
lends itself to batch file transformations or renaming:
@example
ls *.gz | parallel -j+0 "zcat @{@} | bzip2 >@{.@}.bz2 && rm @{@}"
@end example
This will recompress all files in the current directory with names ending
in .gz using bzip2, running one job per CPU (-j+0) in parallel.
If a command generates output, you may want to preserve the input order in
the output. For instance, the following command
@example
@{ echo foss.org.my ; echo debian.org; echo freenetproject.org; @} | parallel traceroute
@end example
will display as output the traceroute invocation that finishes first. Using
the @option{-k} option, as we saw above
@example
@{ echo foss.org.my ; echo debian.org; echo freenetproject.org; @} | parallel -k traceroute
@end example
will ensure that the output of @code{traceroute foss.org.my} is displayed first.
@node Shell Functions
@section Shell Functions
@cindex shell function
@@ -1204,6 +1284,11 @@ shell option has been enabled.
@xref{Bourne Shell Builtins}, for the description of the
@code{trap} builtin.
The @env{FUNCNEST} variable, if set to a numeric value greater
than 0, defines a maximum function nesting level. Function
invocations that exceed the limit cause the entire command to
abort.
If the builtin command @code{return}
is executed in a function, the function completes and
execution resumes with the next command after the function
@@ -3456,6 +3541,11 @@ If the @code{extdebug} shell option is enabled using @code{shopt}
(@pxref{The Shopt Builtin}), the source file name and line number where
the function is defined are displayed as well.
@option{-F} implies @option{-f}.
The @option{-g} option forces variables to be created or modified at
the global scope, even when \fBdeclare\fP is executed in a shell function.
It is ignored in all other cases.
The following options can be used to restrict output to variables with
the specified attributes or to give variables attributes:
@@ -3504,8 +3594,9 @@ with the exceptions that @samp{+a}
may not be used to destroy an array variable and @samp{+r} will not
remove the readonly attribute.
When used in a function, @code{declare} makes each @var{name} local,
as with the @code{local} command. If a variable name is followed by
=@var{value}, the value of the variable is set to @var{value}.
as with the @code{local} command, unless the @samp{-g} option is used.
If a variable name is followed by =@var{value}, the value of the variable
is set to @var{value}.
The return status is zero unless an invalid option is encountered,
an attempt is made to define a function using @samp{-f foo=bar},
@@ -3693,7 +3784,8 @@ Specify the number of lines read between each call to @var{callback}.
If @option{-C} is specified without @option{-c},
the default quantum is 5000.
When @var{callback} is evaluated, it is supplied the index of the next
array element to be assigned as an additional argument.
array element to be assigned and the line to be assigned to that element
as additional arguments.
@var{callback} is evaluated after the line is read but before the
array element is assigned.
@@ -3711,28 +3803,41 @@ printf [-v @var{var}] @var{format} [@var{arguments}]
@end example
Write the formatted @var{arguments} to the standard output under the
control of the @var{format}.
The @option{-v} option causes the output to be assigned to the variable
@var{var} rather than being printed to the standard output.
The @var{format} is a character string which contains three types of objects:
plain characters, which are simply copied to standard output, character
escape sequences, which are converted and copied to the standard output, and
format specifications, each of which causes printing of the next successive
@var{argument}.
In addition to the standard @code{printf(1)} formats, @samp{%b} causes
@code{printf} to expand backslash escape sequences in the corresponding
@var{argument},
In addition to the standard @code{printf(1)} formats, @code{printf}
interprets the following extensions:
@table @code
@item %b
causes @code{printf} to expand backslash escape sequences in the
corresponding @var{argument},
(except that @samp{\c} terminates output, backslashes in
@samp{\'}, @samp{\"}, and @samp{\?} are not removed, and octal escapes
beginning with @samp{\0} may contain up to four digits),
and @samp{%q} causes @code{printf} to output the
beginning with @samp{\0} may contain up to four digits).
@item %q
causes @code{printf} to output the
corresponding @var{argument} in a format that can be reused as shell input.
@item %(@var{datefmt})T
causes @code{printf} to output the date-time string resulting from using
@var{datefmt} as a format string for @code{strftime}(3). The corresponding
@var{argument} is an integer representing the number of seconds since the
epoch. Two special argument values may be used: -1 represents the current
time, and -2 represents the time the shell was invoked.
@end table
@noindent
Arguments to non-string format specifiers are treated as C language constants,
except that a leading plus or minus sign is allowed, and if the leading
character is a single or double quote, the value is the ASCII value of
the following character.
The @option{-v} option causes the output to be assigned to the variable
@var{var} rather than being printed to the standard output.
The @var{format} is reused as necessary to consume all of the @var{arguments}.
If the @var{format} requires more @var{arguments} than are supplied, the
extra format specifications behave as if a zero value or null string, as
@@ -4954,6 +5059,11 @@ Assignments to @env{FUNCNAME} have no effect and return an error status.
If @env{FUNCNAME} is unset, it loses its special properties, even if
it is subsequently reset.
@item FUNCNEST
If set to a numeric value greater than 0, defines a maximum function
nesting level. Function invocations that exceed this nesting level
will cause the current command to abort.
@item GLOBIGNORE
A colon-separated list of patterns defining the set of filenames to
be ignored by filename expansion.
@@ -5855,10 +5965,13 @@ True if @var{file1} is older than @var{file2},
or if @var{file2} exists and @var{file1} does not.
@item -o @var{optname}
True if shell option @var{optname} is enabled.
True if the shell option @var{optname} is enabled.
The list of options appears in the description of the @option{-o}
option to the @code{set} builtin (@pxref{The Set Builtin}).
@item -v @var{varname}
True if the shell variable @var{varname} is set (has been assigned a value).
@item -z @var{string}
True if the length of @var{string} is zero.
@@ -6489,6 +6602,11 @@ is not found.
Non-interactive shells exit if a syntax error in an arithmetic expansion
results in an invalid expression.
@item
Non-interactive shells exit if there is a syntax error in a script read
with the @code{.} or @code{source} builtins, or in a string processed by
the @code{eval} builtin.
@item
Redirection operators do not perform filename expansion on the word
in the redirection unless the shell is interactive.
@@ -6507,6 +6625,19 @@ causes a fatal syntax error in non-interactive shells.
@sc{posix} special builtins are found before shell functions
during command lookup.
@item
The @code{time} reserved word may be used by itself as a command. When
used in this way, it displays timing statistics for the shell and its
completed children. The @env{TIMEFORMAT} variable controls the format
of the timing information.
@item
When parsing and expanding a $@{@dots{}@} expansion that appears within
double quotes, single quotes are no longer special and cannot be used to
quote a closing brace or other special character, unless the operator is
one of those defined to perform pattern removal. In this case, they do
not have to appear as matched pairs.
@item
If a @sc{posix} special builtin returns an error status, a
non-interactive shell exits. The fatal errors are those listed in