On page 329 (Hour 16) of your book Teach Yourself Unix in 24 Hours is the example:

If I try this with this code:

I get:-
syntax error at line 3: `(' unexpected

Are you able to quickly explain what the line test $value < $(echo $string | wc -c) is actually trying to do? I don’t quite understand the $(…) part … and is the < performing a ‘redirection for input’ or is it meant to be ‘less than’?

I have read about 15 chapters of your book (Teach Yourself UNIX in 24 Hours) so far. We are using vi. On the PS1 command, how do I see what is in it so I can add to it and not change what is already there? We are using bash. What I see now is: ctdaywbsdv:/u/gwilki$

When I enter ‘echo $PS1’ I get: $ \[\e[0m\]

How do I keep the above and add the histcmd option? What does the \e and 0m\ mean? What do the [] the square brackets mean? I can’t find a man page for PS1. How do I find the rest of the options for this PS1?

I just finished Learning Unix for Mac OS X Tiger, and think it is an excellent little resource. I'm recently out of school, a school where we weren't taught anything about Unix, just enough to get by. I started work with the data converter team at Agilent labs, and have been able to glean quite a bit off of them (considering many of them were either directly or indirectly responsible for writing many of them commands in common use today). Thus, I'm often embarrassed to ask them questions about exactly some of the stuff you cover in the book.

Okay, now for the question: at work, they have the terminal set up such that the command line works like vi. That is, if I want to search my command history, I simply change mode via escape, type /pattern_to_be_searched, it finds the command, and then I can use other vi commands to change the command a little bit, and then execute it via the shell. How do I set this up in OS X?

This might sound like some wild conspiracy theory, but I'm looking at my music collection and it sure seems like most of them have exactly 12 tracks, no more, no less. Is there some marketing reason this would be the case, or am I witness to some great conspiracy? :-)

I've been trying to copy some files off an FTP archive, but every time I go to do the transfer, it says "Entering Extended Passive Mode" and never gets any further. My conclusion: this passive mode thing is a bust. How can I transfer the files without using passive mode? I'm using ftp from within a Terminal on my Mac, by the way.

Help! For some reason when I try to use "ssh" to connect to my server from my Mac, it fails and is saying that I might be a victim of a "DNS Spoof"? What's going on, and how do I fix the problem?

I need to run a Unix application if a different application is running, from within a shell script. How do I do this?

i need to run a process, PB, and keep it running, for avoiding problems i run it as background providing the user, and password, for connecting to oracle, this with the command:

  PB -u myuser -p my password &

but by using 'ps -ef | grep PB' anyone can see the password. There is another way to run the process, run it in foregroung:

  PB -u myuser

and it prompts for the password
'Enter password:' once typed the process is started.

I would like to run the process in background, but avoiding the password to be shown with any 'ps'?

Last night i started downloading all of Fedora core via rsync. It was getting late, so I put it in the background and logged out. i just logged in this morning, and wanted to see where it was at, so I typed "jobs", but surprise, it isn't there. I know it's still running, because the lights on my hub are still blinking, it shows up in "top", and i can see (du -bs fedora/) that the folder is still growing. How do i get the output back on my terminal?

I want to transfer music and movies to my Sony PSP, on my computer I'm using Suse Linux 9.2. What kind of program or software can I use? The problem is that my computer can't find the Sony PSP when I plug it in the USB port.

I'm new to Mac, last Apple I owned was a IIe in the 80's. This question is related to your book Learning Unix for Mac OS X Tiger book, page 41 "Changing the Command Prompt. In this section you give the following command for changing the prompt:

      PS1= "? "

I typed this, but got the following response from the terminal window:

      -bash: ? : command not found

What am I doing wrong?

Hello I would like to know the what exactly does cat - mean in Unix? I was recently reading through an article that mentioned this command and couldn't understand what it did.

I received this lovely email message from a reader this morning: "Just wanted to thank you for "Teach Yourself Unix in a Week." I read the whole thing cover to cover back in '94, when I was sleeping on a cot at work (!). It got me started in the world of Unix and has provided me employment ever since. My buddy Nick and I owe both you and Kamran Hussein a night of beers for kicking off our sys admin careers."

Dave, I would like to use an environmental variable to change directories and included files into vim on Mac OS Tiger. I've found that this works:
  export pm="/volumes/Macintosh HD/Documents/pmwiki"
for shell commands, but then I have to use something like: cd "$pm"

Is there a better way which doesn't require the double quotes? Also, is there some interaction with the PATH variable?

Dave, we have to do sudo in a shell/perl scripts for certain commands. As you know sudo needs password to be supplied. sudo has -S option for stdin.

For example:

echo $pw | sudo -S command

Assume, somehow, we figure out the password and pass it in for the above echo. But, the buggest concern is, if someone does a "ps", one will be able to see the password. The above example is part of a shell script and what we need to know is how do we hide the password?

How can I delete one file from every place on my disk using Linux? In Windows' I'd open up a command window and use the command

    del archive.txt /s

but what's the Linux equivalent?

Hi Mr.Dave, I am Max from Italy and I am a technician. At the moment I am searching for tutorials or service manuals about DDS2-3 and AIT1-2-3 like the SONY SDT-7000, SDT-9000, SDT-10000 and SONY SDX-300C, SDX-400C, SDX-500C but with no results!! I strongly need these documentations, because i must repair these DAT units. Helicoidal scan technology is used in these devices and our clients use those under SCO OPEN SERVER 5.0.4. I have already requested this material from SONY, but their answer has been negative.

Dave, I read your books Teach Yourself Unix in 24 Hours and Wicked Cool Shell Scripts and since then I can't imagine working again on a system like windows!

My problem is that I've started to make my C files Unix-compatible but I can't find a command for C in Windows that does the same thing as system("cmd") for Unix. Any suggestions?

Dave, I am running an Internet Café in which I have about 10 workstations and one server. Now I am planning to configure a proxy server on LINUX for my cafe to improve performance in browsing. For this I have installed Complete REDHAT 9.0 in a machine equiped with 1.3G RAM, 80GB HDD, 1GHz MP, Intel P4, plus 2 NICs (Real Tech). But I have no idea about how to configure PROXY on it. Kindly let me know about any links or tutorial which can help me in a jumpstart. I do not want to mess with linux deeper. I just want to sonfigure PROXY and that is it.

Dave, I have searched the web over and can't seem to find an appropriate answer to this question. I have a need for a script that will create millions of 1-5Kbyte files in a linux filesystem for testing purposes. I have to do this on a regular basis and it would be really cool to have it scripted. I am not sure what the quickest way to do this would be?

Dave, how can I flatten a directory structure? I've got a directory "foo", with many more sub-directories and files within. I want to take all the files from all levels beneath foo and put them in foo itself.

I've tried this: find . *.mp3 -print0 | xargs -0 mv . but I get an error on the mv command that I can't figure out. Help!

Dave, I am a Sun Solaris sysadmin and really liked your book Wicked Cool Shell Scripts. However, I don't seem to find the "rev" utility on any of my Sun servers running Solaris 2.6, 7, 8, and even 9. I couldn't find it on the sunfreeware.com site either. Could you tell me where I can find it?

Dave, I want to copy a directory tree BUT I want to specify the root of the operation and the destination directory and then specify name/type patterns a la find. The result I want is the root at the destination and then only the directories which have files that match the pattern and the files themselves. Does that make sense?

Dave, Why is it that, "out of the box", the Firefox browser looks great (font wise) when run on a Windows OS but looks terrible (almost too small and unreadable) on any Linux OS I have tried it on. It is probably the number one killer reason for me not switching to Linux.

Dave, I have a straightforward Linux question that's got me stumped. I have a directory with lots of files that include an underscore, but I want to produce a listing of files that don't have the underscore, not those that do have it. I can get it with a combination of ls, grep -v and such, but it's painful and convoluted. Is there a simpler solution?

I've been migrating to Ximian Evolution on my Linux box and I love it, but I haven't been able to figure out how to set up all the mailing list rules I want to add to the program. Can you help me figure out how to set up a mailing list rule?

Dave, I need to conduct a number of searches through more than 2500 text files. Each search is for a different specific text string. The text files are on my Mac hard drive (Mac OS X 10.3.7) and are arranged into folders within folders within folders. I want the result in a new text file. I think I should be able to do this using some sort of grep or script but cannot figure out how to do it. Please help.

Dave, I know you can't solve trivial questions for everyone, but if you could have someone help me with the umask command and the content on pp. 107-109 of your book Teach Yourself Unix is 24 Hours, I'd appreciate it. I've taken two hours to try to figure out how in the world umask 277 produces a read-only file. It seems to me it would be write only. Can you shed some light on this, please?

Dave, I have a number of different computers running Mac OS X, and would like to keep my Safari bookmarks in sync. I don't necessarily need to to have these bookmarks accessible within other Web browsers (though it'd be a bonus if Firefox saw them too) but if I designate one as my master bookmark file, is there any way to have my other Safari browsers stay synchronized?

Dave, I purchased your Wicked Cool Shell Scripts book a month or so ago (great book), and have used it to "learn by example" in writing some shell scripts, as I've a long way to go in this area.

I need to rotate logs on an IBM AIX 5.1 Unix box, and tried using your script #55, rotatelogs for this but it didn't work, as -maxdepth is not supported in AIX's find command. So, I commented it out, and it worked, but also rotated everything in the subdirectories as well (no problem...backed up directory first, then restored). I am trying to get it to work using -prune which my search in Google found to be a good fix for the lack of �maxdepth, but it's not doing what I want. Help!

Dave, I ran across your sites and Wicked Cool Shell Scripts book while trying to convince myself that `sleep 0` is a valid and relatively portable command to use freely in my unix shell scripts.

I looked at a few of the Bourne shell scripts and they seem to use constructs like $( ... ) and $(( ... )) which are not standard Bourne shell (to my understanding). So I actually have three questions, rather than just one:

1. In what flavor of /bin/sh are those scripts written?
2. Can you suggest any references regarding writing portable (Bourne) shell scripts?
3. I would love to find an equivalent reference for what unix utilities *and options* to use for increasing script portability. Any suggestions?

Dave, using SpamAssassin, how do I proceed with content filtering? I want to block 15 words that can appear in the email being sent to me. I already have SpamAssassin set up on my Linux system, I just need to figure out how to configure the rules file properly!

On a mailing list I'm on, someone asked an interesting question about the du command: "I want to figure out how much disk space I'm using in different directories, but I don't know how to exclude certain directories from the output. Anyone have a suggestion?"

A reader writes to me: "I work with HumaniNet, an organization that assists humanitarian field teams with their communications needs, mostly over satellite. Bandwidth is typically very expensive, in the dollars per minute range. Am I correct to assume that Lynx doesn't even request images or other forms of 'rich content' like Flash, and would therefore save dramatically on bandwidth costs? In other words, Lynx doesn't download anything beyond (x)html, right?"

A reader writes in to me, asking whether I think that the Lynx web browser, a command-line screen-oriented alternative to the big, splashy graphical web browsers like Firefox, Mozilla, Safari and Internet Explorer, has any relevance in the modern world of technology and broadband. It's a fair question, and in fact I just published an article in SysAdmin Magazine on this subject.

A reader writes:

I had taken an intro course to UNIX a few years ago, but have found your book Teach Yourself Unix in 24 Hours MUCH more comprehensive and user-aware!

I have hit a stumbling block in Chapter 16 (page 337) where you illustrate the use of cat, however. You show:

$ cat average.awk
NF > 2 { count += 1
        totalsize += $5
}

There is more that follows on this page and page 338. This seems to illustrate that the cat command allows you to input text into the named file. Perhaps that is not what you meant. Did I miss something?

A reader writes:

I've just bought your Teach Yourself Unix in 24 hours, and I have to tell you that I love the book. I always answer the questions at the end of each chapter without knowing whether I get it right or wrong. Do you provide solutions to those answer questions?

A reader writes:

So, I'm partway through your book, and I want to check on hard links. When you say it creates another door to the same body of data, is that literally true? For example, if all I have in my ./Documents directory is 001.doc (size 512K), and I hard link as hardlink.doc then run ls, do I see A or B?

A) 001.doc 512K
hardlink.doc 512K
total 1024K

B) 001.doc 512K
hardlink.doc 512K
total 512K

If it's not B, I'm not sure what the point is, other than maybe not changing the timestamp.

A reader of Learning Unix for Mac OS X Panther writes in to ask for an explanation of the regular expression shown in this command:

du -s * .[^.]*

I'm working on the Web site for Creating Cool Web Sites and just realized that the little Unix trick I used while editing a file is actually a beautiful example of why so many people love Unix so much, so I thought I'd share it. The problem: a file where lines have 1-10 words + a last field value (in this case, a page number) that I don't want. The challenge is to figure out how to easily remove that last field, when there are a variable number of fields on the line.

A reader writes:

"I've got a few of your books and today picked up Wicked Cool Shell Scripts, which I'm very much looking forward to working with.

"Totally greenhorn question, though: I want to keep the scripts in ~/bin and on page 12 you have an italic note saying to edit our PATH variable, but I'm not sure how, and don't see any instructions anywhere else as to how to do this. I would be perfectly happy to have ~/scripts as you suggest but have not been able to create either. Your other book Learning Unix for Mac OS X doesn't appear to show how to do this with BASH. Many thanks in advance."

A reader writes:

"At the end of TYU24, you mention MKS as a Windows-based shell. I checked their website as an avenue of learning Unix/Linux without resorting to dual-boots, or multiple systems (I'm a little short on space to accomidate another tower, and short on cash to build a new micro). While they do offer evaluation versions, and educational discounts, they are still a little steep on the price range. Is there another package that may follow GPL (GNU Public License) or maybe a more cost effective package for home use?"

In just 24 sessions of one hour or less, readers of Teach Yourself Unix in 24 Hours will be up and running with UNIX, the operating system at the heart of the Internet.