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Full Discussion: help running strace
Top Forums UNIX for Advanced & Expert Users help running strace Post 302089986 by klam on Thursday 21st of September 2006 08:03:59 PM
Old 09-21-2006
help running strace

OK so I wanted to know how does grep outputs to the pipe and how sort reads from it. So I run a strace over "grep blah myfile | sort" and this is what I got:

open("myfile", O_RDONLY|O_LARGEFILE) = 3
fstat64(3, {st_mode=S_IFREG|0600, st_size=84, ...}) = 0
read(3, "blah blah and blah cause of blah"..., 32768) = 84
fstat64(1, {st_mode=S_IFIFO|0600, st_size=0, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7fe8000
read(3, "", 32768) = 0
close(3) = 0
write(1, "blah blah and blah cause of blah"..., 85) = 85
close(1) = 0
munmap(0xb7fe8000, 4096) = 0
exit_group(0) = ?
Process 14533 detached
blah blah and blah cause of blah
find blah myfile blah grep it.
this is my blah file

I know that grep nor sort are aware of the pipe, they just input/output to the stdin/stdout... the pipe just connect them, that's how pipes works as far as I know... but what I don't see in this code is how grep is outputing to the pipe (stdout) and how is sort reading from the pipe (stdin). Is there anyway to check that relation? All I can tell from the code I bolded is:

MyFile -> Grep --------------------------> stdout

Unless "read(3, "", 32768)" has anything to do with the sort process.
Thanks in advance.
 

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radiusd.conf(5) 					   FreeRADIUS configuration file					   radiusd.conf(5)

NAME
radiusd.conf - configuration file for the FreeRADIUS server DESCRIPTION
The radiusd.conf file resides in the radius database directory, by default /etc/raddb. It defines the global configuration for the FreeRA- DIUS RADIUS server. CONTENTS
There are a large number of configuration parameters for the server. Most are documented in the file itself as comments. This page docu- ments only the format of the file. Please read the radiusd.conf file itself for more information. The configuration file parser is independent of the server configuration. This means that you can put almost anything into the configura- tion file. So long as it is properly formatted, the server will start. When the server parses the configuration file, it looks only for those configurations it understands. Extra configuration items are ignored. This "feature" can be (ab)used in certain interesting ways. FILE FORMAT
The file format is line-based, like many other Unix configuration files. Each entry in the file must be placed on a line by itself, although continuations are supported. The file consists of configuration items (variable = value pairs), sections, and comments. Variables Variables can be set via: name = value Single and double-quoted strings are permitted: string1 = "hello world" string2 = 'hello mom' Sections A section begins with a section name, followed on the same line by an open bracket '{'. Section may contain other sections, com- ments, or variables. Sections may be nested to any depth, limited only by available memory. A section ends with a close bracket '}', on a line by itself. section { ... } Sections can sometimes have a second name following the first one. The situations where this is legal depend on the context. See the examples and comments in the radiusd.conf file for more information. section foo { ... } Comments Any line beginning with a (#) is deemed to be a comment, and is ignored. Comments can appear after a variable or section defini- tions. # comment foo = bar # set variable 'foo' to value 'bar' section { # start of section ... } # end of section Continuations Long lines can be broken up via continuations, using '' as the last character of the line. For example, the following entry: foo = "blah blah blah" will set the value of the variable "foo" to "blah blah blah". Any CR or LF is not turned into a space, but all other whitespace is preserved in the final value. REFERENCES
The value of a variable can reference another variable. These references are evaluated when the configuration file is loaded, which means that there is no run-time cost associated with them. This feature is most useful for turning long, repeated pieces of text into short ones. Variables are referenced by ${variable_name}, as in the following examples. foo = bar # set variable 'foo' to value 'bar' who = ${foo} # sets variable 'who' to value of variable 'foo' my = "${foo} a" # sets variable 'my' to "bar a" If the variable exists in a section or subsection, it can be referenced as ${section.subsection.variable}. Forward references are not allowed. Relative references are allowed, by pre-pending the name with one or more period. blogs = ${.foo} Will set variable blogs to the value of variable foo, from the current section. blogs = ${..foo} Will set variable blogs to the value of variable foo, from the section which contains the current section. blogs = ${modules.detail.filename} Will set variable blogs to the value of variable filename, of the detail module, which is in the modules section of the configuration file. Properties of anonymous parent sections may also be referenced, currently name and instance are supported. modules { example foo { file = ${.:name} } } Will set variable file to the name of the containing section (example). modules { example foo { file = ${.:instance} } } Will set variable file to the instance name of the containing section (foo). modules { example foo { file = ${..:name} } } Will set variable file to the name of the parent of the containing section (modules). FILES
/etc/raddb/radiusd.conf SEE ALSO
radiusd(8) unlang(5) AUTHOR
Alan DeKok <aland@freeradius.org> 28 Jun 2013 radiusd.conf(5)
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