|
|
by Richard Burton
The Missing Argument Chapter
This series is designed to help you learn more about the Mac OS X command line. If you have any questions about what you read here, check out the earlier columns, write back in the comments below, or join us in Hardcore X! forum. [Editor's Note: This installment was originally planned to be run as Part III of this series, and should be read before the piece actually published as Part III, Understanding Metacharacters. As such, we are publishing it early this week for those working along with the series, numbered as Part IV.] Now that we've taken a look at some basic commands, let's examine two key, related features of Unix commands: arguments and options. We saw command arguments in the previous column. Remember the cd command? [localhost:~] dr_unix% pwd /Users/dr_unix [localhost:~] dr_unix% cd Sites [localhost:~/Sites] dr_unix% pwd /Users/dr_unix/Sites [localhost:~/Sites] dr_unix% cd [localhost:~] dr_unix% pwd /Users/dr_unix [localhost:~] dr_unix% When we typed the command cd Sites to change our current working directory, we told the computer that 'Sites' is the target directory. 'Sites' is the argument to the cd command. Recall that, if cd is given no argument, it defaults to the user's home directory. Also, most, if not all, Unix commands will check to see if an argument is valid before running the intended operation. (And if one doesn't, it should.) [localhost:~] dr_unix% cd Lirbary Lirbary: No such file or directory. [localhost:~] dr_unix% Some commands are very persnickety about how many arguments they take, and will insist on the proper number. Others are more devil-may-care, and will take however many you wish. However, the behavior may vary by the number of arguments. [localhost:~] dr_unix% cd Music Pictures cd: Too many arguments. [localhost:~] dr_unix% Check the man page for a particular command for the details. Take ls as an example of a command that can take any number of arguments. Recall that if you give it no arguments ls will print a list of all the files in your current working directory. [localhost:~] dr_unix% pwd /Users/dr_unix [localhost:~] dr_unix% ls Adam.txt Documents Movies Pictures Sites test_1.txt Desktop Library Music Public personal who_list [localhost:~] dr_unix% If, however, you pass ls an argument, the behavior changes. It the argument is a file, you get the name of the file. [localhost:~] dr_unix% ls who_list who_list [localhost:~] dr_unix% That isn't too useful. However, if the argument is a directory, you get a list of files in that directory. [localhost:~] dr_unix% ls Sites images index.html [localhost:~] dr_unix% ls Sites/images apache_pb.gif macosxlogo.gif web_share.gif [localhost:~] dr_unix% While that is useful, it is also a bit limited. Fortunately, ls is more powerful than we've seen so far. For one thing, it can take any number of arguments. [localhost:~] dr_unix% ls test_1.txt who_list test_1.txt who_list [localhost:~] dr_unix% Also, ls is clever enough that you can combine regular files with directories. [localhost:~] dr_unix% ls test_1.txt Library Movies test_1.txt Movies: Sites: images index.html [localhost:~] dr_unix% Notice how the directories are separated from the regular files, and how the directories are separated from each other. Also, notice that the Movies directory is listed, but as it contains no files, nothing is listed under it. While lists of files are handy to know, you often want to know things like: how big are these files, when were they last changed, etc. ls provides this if you use different options. Options are small flags that you pass to a command to slightly alter or refine its behavior. The options are denoted by starting with a '-' and come before arguments to the command start. The behavior of the options, and which ones are valid, varies by command. If you are unsure about what is available for a particular command, remember that you can always check the man page. For ls, many options are available, but I'll use a few of the more common ones as examples. One of the most useful is the '-l' option, which gives a LOT of information. [localhost:~] dr_unix% ls -l total 24 -rw-r--r-- 1 dr_unix staff 15 Mar 25 17:28 Adam.txt drwx------ 7 dr_unix staff 194 Mar 25 17:25 Desktop drwx------ 18 dr_unix staff 568 Mar 25 09:48 Documents drwx------ 26 dr_unix staff 840 Mar 17 12:42 Library drwx------ 2 dr_unix staff 264 Mar 21 20:30 Movies drwx------ 2 dr_unix staff 264 Mar 21 20:30 Music drwx------ 6 dr_unix staff 264 Mar 21 20:30 Pictures drwxr-xr-x 4 dr_unix staff 264 Mar 22 18:06 Public drwxr-xr-x 4 dr_unix staff 264 Aug 21 2001 Sites drwxr-xr-x 7 dr_unix staff 264 Mar 23 11:21 personal -rw-r--r-- 1 dr_unix staff 15 Mar 18 10:47 test_1.txt -rw-r--r-- 1 dr_unix staff 243 Mar 18 10:47 who_list [localhost:~] dr_unix% So, just what does all this mean? The first character tells us whether the file is a directory (d) or a regular file (-). (There are other possibilities, but don't worry about that for now.) The next nine characters show the permissions on each file. For each file, there are three levels of permission: read (r), write (w), and execute (x). The first three show permission for the file's owner, the second three for anyone else in the same user group, and the final three for the rest of the world. (If you aren't familiar with user groups, don't sweat it.) Next comes the number of links (again, don't sweat it), followed by the file's owner, the file's user group, the size of the file, the date it was last altered, and finally the name of the file. Normally, ls on the Mac sorts in ASCII order, which is alphabetical by capital letters followed by alphabetical by lowercase. If you want to list in reverse order, you can use the '-r' option. [localhost:~] dr_unix% ls Adam.txt Documents Movies Pictures Sites test_1.txt Desktop Library Music Public personal who_list [localhost:~] dr_unix% ls -r who_list personal Public Music Library Desktop test_1.txt Sites Pictures Movies Documents Adam.txt [localhost:~] dr_unix% Or if you want to sort from newest to oldest, use the '-t' option. [localhost:~] dr_unix% ls -t Adam.txt Documents Public Pictures who_list Library Desktop personal Music Movies test_1.txt Sites [localhost:~] dr_unix% What if you want to sort from oldest to newest? You can just combine the '-t' and '-r' options. This can be entered as ls -t -r. For convenience (i.e. laziness), you can combine flags, like ls -tr. [localhost:~] dr_unix% ls -rt Sites test_1.txt Movies Music personal Desktop Library who_list Pictures Public Documents Adam.txt [localhost:~] dr_unix% Or, going hog-wild, [localhost:~] dr_unix% ls -lrt total 24 drwxr-xr-x 4 dr_unix staff 264 Aug 21 2001 Sites drwx------ 26 dr_unix staff 840 Mar 17 12:42 Library -rw-r--r-- 1 dr_unix staff 15 Mar 18 10:47 test_1.txt -rw-r--r-- 1 dr_unix staff 243 Mar 18 10:47 who_list drwx------ 2 dr_unix staff 264 Mar 21 20:30 Movies drwx------ 6 dr_unix staff 264 Mar 21 20:30 Pictures drwx------ 2 dr_unix staff 264 Mar 21 20:30 Music drwxr-xr-x 4 dr_unix staff 264 Mar 22 18:06 Public drwxr-xr-x 7 dr_unix staff 264 Mar 23 11:21 personal drwx------ 18 dr_unix staff 568 Mar 25 09:48 Documents drwx------ 7 dr_unix staff 194 Mar 25 17:25 Desktop -rw-r--r-- 1 dr_unix staff 15 Mar 25 17:28 Adam.txt [localhost:~] dr_unix% One other very handy option for ls is '-a'. This shows all files: [localhost:~] dr_unix% ls -a . .Trash Library personal .. .ssh Movies test_1.txt .CFUserTextEncoding .tcsh_history Music who_list .DS_Store Adam.txt Pictures .FBCIndex Desktop Public .FBCLockFolder Documents Sites [localhost:~] dr_unix% The files that start with a '.' are known as "hidden files". Normally they are files that hold your personal settings for particular applications (.mailrc for the Unix mail application, for example). Normally, you want to ignore them, so ls defaults to not printing them. And of course, '-a' can be combined with other options, and yes Virginia, hidden files can also be directories: [localhost:~] dr_unix% ls -al total 120 drwxr-xr-x 21 dr_unix staff 670 Mar 25 17:46 . drwxr-xr-t 4 root wheel 92 Mar 13 16:54 .. -rw-r--r-- 1 dr_unix staff 3 Mar 17 12:38 .CFUserTextEncoding -rw-rw-rw- 1 dr_unix staff 6148 Mar 25 17:46 .DS_Store -rw-rw-rw- 1 dr_unix staff 32768 Mar 21 20:29 .FBCIndex drwxrwxrwx 3 dr_unix staff 58 Mar 21 20:29 .FBCLockFolder drwx------ 4 dr_unix staff 92 Mar 25 17:25 .Trash drwx------ 2 dr_unix staff 24 Mar 12 18:26 .ssh -rw------- 1 dr_unix staff 1919 Mar 25 17:19 .tcsh_history -rw-r--r-- 1 dr_unix staff 15 Mar 25 17:28 Adam.txt drwx------ 7 dr_unix staff 194 Mar 25 17:25 Desktop drwx------ 18 dr_unix staff 568 Mar 25 09:48 Documents drwx------ 26 dr_unix staff 840 Mar 25 17:46 Library drwx------ 2 dr_unix staff 24 Mar 21 20:30 Movies drwx------ 2 dr_unix staff 24 Mar 21 20:30 Music drwx------ 6 dr_unix staff 160 Mar 21 20:30 Pictures drwxr-xr-x 4 dr_unix staff 92 Mar 22 18:06 Public drwxr-xr-x 4 dr_unix staff 92 Aug 21 2001 Sites drwxr-xr-x 7 dr_unix staff 194 Mar 23 11:21 personal -rw-r--r-- 1 dr_unix staff 15 Mar 18 10:47 test_1.txt -rw-r--r-- 1 dr_unix staff 243 Mar 18 10:47 who_list [localhost:~] dr_unix% Two of these files that deserve our attention for now are the '.' and '..' directories. '.' means 'this directory'. [localhost:~] dr_unix% ls . Adam.txt Documents Movies Pictures Sites test_1.txt Desktop Library Music Public personal who_list [localhost:~] dr_unix% ls Adam.txt Documents Movies Pictures Sites test_1.txt Desktop Library Music Public personal who_list [localhost:~] dr_unix% This may seem silly, but later we will see how handy this is. '..' represents 'the directory above this one': [localhost:~] dr_unix% pwd /Users/dr_unix [localhost:~] dr_unix% cd .. [localhost:/Users] dr_unix% pwd /Users [localhost:/Users] dr_unix% So we can see, even from these limited examples, that arguments and options give Unix commands a lot of power and flexibility, yet they do it in a very compact, some would say elegant, way. The real power of ls, and a key feature of the Unix command line, lies in the wildcard feature, which we'll see in the next column.
You are encouraged to send Richard your comments, or to post them below. Most Recent Mac OS X Command Line 101 Columns Command Line History & Editing Your Commands Pico: An Easy To Use Command Line Editor Understanding The "grep" Command In Mac OS X Command Line History & Editing Your Commands Mac OS X Command Line 101 Archives Back to The Mac Observer For More Mac News!
Richard Burton is a longtime Unix programmer and a handsome brute. He spends his spare time yelling at the television during Colts and Pacers games, writing politically incorrect short stories, and trying to shoot the neighbor's cat (not really) nesting in his garage. He can be seen running roughshod over the TMO forums under the alias tbone1. |
|
|
|||||||||||||||||||||||||
 |
© All information presented on this site is copyrighted by The Mac Observer except where otherwise noted. No portion of this site may be copied without express written consent. Other sites are invited to link to any aspect of this site provided that all content is presented in its original form and is not placed within another . |
 |
