When googling for linux commands, I often see a number in parenthesis like this:     mklost+found(8)   What does it mean? Is it a version number of the program, reference to some standard, or what?
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So, for example, when I type man ls I see LS(1). But if I type man apachectl I see APACHECTL(8) and if I type man cd I end up with cd(n).  I'm wondering what the significance of the numbers in the parentheses are, if they have any.
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If parsing the output of ls is dangerous because it can break on some funky characters (spaces, \n, ... ), what's the best way to know the number of files in a directory?  I usualy rely on find to avoid this parsing, but similarly, find mydir | wc -l will break for the same reasons.  I'm working on Solaris right now, but I'm looking for a answer as portable across different unices and different shells as possible.
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there is a script I evolved with it, it has line of command like below :  mytemp=`echo ${sourcedir}|awk -F/ '{printf "/%s/tmp",$2}'`/`basename $0`-$1.$$   at the last of the command we see $$ that produces a number. when I use echo $$ in bash I also see a number like bellow:   #echo $$  23019   what exactly is this number, and what is $$?
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Does anyone knows how can I use square brackets instead of parenthesis when numbering my equations?  I used this command:  \begin{equation} y = 2x \end{equation}     The number appears on the right hand side like (1) I want to make it [1].  Does anyone have any ideas?
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If I have a number of directories, named, for example 10001 through 10025 is there any reason to use ls 1*/foo vs. ls 100??/foo?  I have a lot more than 25 of them, so I mostly curious if there's any differences in speed.  I know the difference in use between the two, that the asterisk will match longer file names, like 10001.backup. But let's say I don't have any files that don't follow my conventions. Is there any behind-the-scenes differences?
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While researching another problem, I ,  locate something | xargs -I {} bash -c "if [ -d "{}" ]; then echo {}; fi"   that I wanted to learn more about.  So I ran man xargs and get the following output:  XARGS(1)                    General Commands Manual                   XARGS(1)  NAME        xargs - build and execute command lines from standard input  SYNOPSIS        xargs  [-0prtx]  [-E  eof-str] [-e[eof-str]] [--eof[=eof-str]] [--null]        [-d delimiter] [--delimiter delimiter]  [-I  replace-str]  [-i[replace-        str]]    [--replace[=replace-str]]   [-l[max-lines]]   [-L   max-lines]        [--max-lines[=max-lines]] [-n max-args] [--max-args=max-args] [-s  max-        chars]  [--max-chars=max-chars]  [-P max-procs] [--max-procs=max-procs]        [--interactive]      [--verbose]      [--exit]      [--no-run-if-empty]        [--arg-file=file]   [--show-limits]   [--version]   [--help]   [command        [initial-arguments]]  DESCRIPTION        This manual page documents the GNU version of xargs...   I am trying to get better at using documentation to learn about Linux programs, but that "Synopsis" section is intimidating to new users.  It literally looks like gibberish compared to man locate or man free.  So far, I understand that square brackets mean optional and nested brackets mean options in optional.  But how am I supposed to induce a valid command with that?  I am not asking for help with xargs here.  I am looking for help interpreting a man page to understand complicated commands.  I want to stop making Google-indexed web blogs and personal help from others my first approach to learning Linux commands.
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While reading up on how to set up grub, I came across an article claiming that I need to use one of the following two syntaxes,  echo \(hd0,0\) &gt;&gt; /boot/grub/grub.conf   or  echo '(hd0,0)' &gt;&gt; /boot/grub/grub.conf   because, at the command line, parentheses are interpreted in a special way. What is special about the parentheses? How are they interpreted?
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The question is pretty straight forward. I can get the exit code of the previous command by using $?. But what exactly is it?  I don't think it is a variable, because you can't have any special characters in the name of variable other than _.  foo?foo=10   will result in the error: foo?foo=10: command not found  So if it is not a variable, what is it? Are there others like it?
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Simple question, but I'm not sure where to look and google doesn't respond to periods and slashes.  I'm just trying to count the # of files &amp; directories in the current directory (not including subfolders/files) and was trying to differentiate ls -1 | wc -l and ls | wc -l since they seem identical.  A site I was looking at said "Keep in mind that this is also counting the ./ and ../ directories." regarding the one with ls -1, and I'm not sure if that means it includes the directories before or something (which I don't want), but it didn't seem to do that from testing.  Could someone confirm which one of those would be most adequate for counting # of files &amp; directories in the current directory only (not sub) and what they mean by ./ and ../ directories?
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Example: In a Terminal command xdpyinfo | grep resolution (that I have taken from an answer), does the | character mean that the xdpyinfo output shall be sent to the grep program input for printing a line containing the resolution string? Where should I seek for such an information to avoid filling this forum by too simple questions? Thanks.
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Sometimes I see chmod commands that use four octal digits instead of three -- what is the optional first digit for? For example, chmod 777 is equivalent to chmod a+rwx; what's the same command for chmod 2777?
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I found it in an old dictionary and I'm not sure what it means. It looks like the number &quot;3&quot;, but the top of the three has been flattened(and slightly curved). I've only seen this in three or four words. []
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So, when a command is not found, by what means is the "did you mean:" list populated? What program finds these alternate commands?  What is the meaning of: "(main), (universe)..."? Can I change which program finds these?
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What is the difference between absolute / canonical / relative paths?  I guess that absolute starts with a /. Can it contain /../?  Is a canonical path different from an absolute path in that it can't contain /../?  Is foo a relative path?  Googling posix canonical path didn't turn up much... What are the POSIX references for these terms?
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Possible Duplicate:          Most commands I use in linux behave exactly the same whether I include the trailing slash / character on the end of a directory name or not.  For example:  ls /home/cklein ls /home/cklein/  cp foo bar cp foo/ bar/   When does this trailing slash matter?  What is the semantic meaning of the trailing slash?
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When I enter single quote ' in terminal it goes to some other mode, and commands don't execute. What is this mode and when do we use it?  root@sai:~# ' &gt; ls &gt; ' ls : command not found root@sai:~#
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Trying to write -regex for a find statement that shows only directories with dots and numbers, for example 1.2.3.4 oraz 1.2.3 or 1.3.4.5.6 was trying something like  "-regex '\.[0-9.]+'", but it also shows dirs with letters. And I only want directories with numbers and dots.