Seeing the Contents of Directories

Seeing the Contents of Directories

We normally think of a directory as "containing" files, but in reality a directory is just a special kind of file. A directory contains a list of entries. Each entry is the name of a file or another directorythis is an important concept. In Unix, the only place where a file's name is stored is in the directory. Filenames are not stored inside the files themselves .

When you rename a file, you are changing the entry in a directory, but not changing the file. And when you remove a file, you are removing the file's name from a directory.

The operating system removes the file if there are no other directory entries for that file. This becomes very important when trying to understand hard links , which are described below in the section "About Links (the Unix Version of Aliases)." (Hard links are a way of having more than one directory entry that refers to the same actual file.)

To list the contents of the current directory:

• ls
  
  You see all of the nonhidden entries in the current directory (see below for an explanation of hidden files and how to view them).
  
  

To list the contents of any directory:

• ls path
  
  If path is a directory, then the contents of the directory are shown. The path is always optional with the ls command. If it is omitted, the default path is . (the current directory).
  
  You can list the contents of several directories by specifying multiple paths on the command line. Figure 5.13 shows the output from the command line
  
  ls /bin /sbin
  
  (Each of the files listed is actually a command. Use the man command described in Chapter 4, "Useful Unix Utilities," to learn about each of them.)
  
  

  Figure 5.13. Supplying multiple arguments to ls to see the contents of more than one directory.

   localhost:~ vanilla$  ls /bin /sbin  /bin: [                df                   launchctl           pwd           tcsh bash             domainname           link                rcp           test cat              echo                 ln                  rm            unlink chmod            ed                   ls                  rmdir         wait4path cp               expr                 mkdir               sh            zsh csh              hostname             mv                  sleep         zsh-4.2.3 date             kill                 pax                 stty dd               ksh                  ps                  sync /sbin: SystemStarter           md5                          newfs_msdos Autodiskmount           mknod                        nfsd Clri                    mount                        nfsiod Disklabel               mount_afp                    nologin Dmesg                   mount_autofs                 ping Dump                    mount_cd9660                 ping6 Dumpfs                  mount_cddafs                 quotacheck dynamic_pager           mount_devfs                  rdump fibreconfig             mount_fdesc                  reboot fsck                    mount_ftp                    restore fsck_hfs                mount_hfs                    route fsck_msdos              mount_msdos                  routed halt                    mount_nfs                    rrestore ifconfig                mount_ntfs                   rtsol ip6fw                   mount_smbfs                  service ipfw                    mount_synthfs                shutdown kerberosautoconfig      mount_udf                    slattach kextload                mount_volfs                  tunefs kextunload              mount_webdav                 umount launchd                 newfs launchd_debugd          newfs_hfs localhost:~ vanilla$ 

  
  

Hidden files

Unix normally does not show you files whose names begin with a . (a period, or dot in Unix-speak). These dot files are typically configuration files that are used by programs such as your shell when they start up, and thus they are something like the preferences files that littered your System Folder in preOS X versions of the Mac OS. See the sidebar "More About Hidden Files" for details.

To see hidden files:

• Use the -a or -A option to ls .
  
  Unix (and the Mac OS X Finder) hides files whose names begin with a . (dot).
  
  Adding the -a option shows all dot files ( -a for all files ).
  
  The -A option is the same as -a except that the two special directory names . and .. are not shown. In this case, it's -A for almost all .
  
  Figure 5.14 compares the output of
  
  

   ls ls -a ls -A 

  
  

  Figure 5.14. Using the -a and -A options to ls reveals dot files. Your output may be different.

   localhost:~ vanilla$  ls  Current Projects          Library             Pictures           bin Desktop                   Movies              Public             system-status Documents                 Music               Sites localhost:~ vanilla$  ls -a  .                         .lpoptions          Music ..                        .ssh                Pictures .CFUserTextEncoding       .viminfo            Public .DS_Store                 Desktop             Sites .Trash                    Documents           Stuff .bash_history             Library             bin .bash_profile             Movies localhost:~ vanilla$  ls -A  .CFUserTextEncoding       .ssh                Music .DS_Store                 .viminfo            Pictures .Trash                    Desktop             Public .bash_history             Documents           Sites .bash_profile             Library             Stuff .lpoptions                Movies              bin localhost:~ vanilla$ 

  
  

Getting more information from ls

The -l option to ls gives the "long" form of its output, listing one line for each entry and giving information about the file's size , date of last change, and other information.

See the section "Getting Information About Files and Directories," later in this chapter, for more on the -l option.

Sorting the output of ls

The default for ls is to sort its output alphabetically . By using the -t option you can cause the output to be sorted according to the time the file was last changed.

To sort the list by time instead of name:

• Use the -t option to ls .
  
  This is most useful when it's combined with the -l option (for example, ls -lt *.jpg ), because the -l option causes the modification date and time to be displayed.
  
  Figure 5.15 compares the output of ls -l with ls -lt .
  
  

  Figure 5.15. Adding the -t option causes ls to sort by the time of last modification.

   localhost:~/Documents vanilla$  ls -l  total 48 -rw-r--r--       2 vanilla     staff      55 Jan           2 17:37 foo -rw-r--r--       1 vanilla     staff      331 May          8 19:04 novel.txt -rw-r--r--       1 vanilla     staff      134 May          8 19:06 report.txt -rw-r--r--       2 vanilla     staff      55 Jan           2 17:37 test1.txt -rw-r--r--       1 vanilla     staff      87 Jan           2 17:38 test2.txt -rw-r--r--       1 vanilla     staff      62 Jan           2 17:38 test3.txt drwxr-xr-x       3 vanilla     staff      264 May          5 13:39 vi-practice localhost:~/Documents vanilla$  ls -lt  total 48 -rw-r--r--       1 vanilla     staff      134 May          8 19:06 report.txt -rw-r--r--       1 vanilla     staff      331 May          8 19:04 novel.txt drwxr-xr-x       3 vanilla     staff      264 May          5 13:39 vi-practice -rw-r--r--       1 vanilla     staff      62 Jan           2 17:38 test3.txt -rw-r--r--       1 vanilla     staff      87 Jan           2 17:38 test2.txt -rw-r--r--       2 vanilla     staff      55 Jan           2 17:37 foo -rw-r--r--       2 vanilla     staff      55 Jan           2 17:37 test1.txt localhost:~/Documents vanilla$ 

  
  

To reverse the sort order:

• Use the -r option ( r for reverse ).
  
  Figure 5.16 compares the output of ls with ls -r .
  
  

  Figure 5.16. Using the -r option causes ls to reverse the sorted order of its output.

   localhost:~/Public vanilla$  ls  cgi-bin               dancer         images            index.html       upload.html localhost:~/Public vanilla$  ls -r  upload.html           index.html     images            dancer           cgi-bin localhost:~/Public vanilla$ 

  
  

Tip

• If you want to find out which files in a directory were most recently modified, use ls with the l , t , and r options:

  ls -ltr

  That puts the most recently modified files at the bottom of the list, so even if the list of files is very long, the last thing on your screen is the most recently modified file.

To list only files matching a pattern:

See the entry on command-line wildcards in Chapter 2 or pipe the output of ls tHRough grep (review Chapter 4 or man grep ).

Sometimes you will want to list everything in a directory, including what's in any subdirectories, and any subdirectories of those directories, and so on. This is known as a recursive listing. There is an easy way to do this:

To recursively list the contents of a directory:

• ls -R path
  
  If path is a directory, then ls recursively lists the contents of path and its subdirectories (in this case, R is for recursive ). Figure 5.17 compares the output from
  
  ls ~/Sites
  
  and
  
  ls -R ~/Sites
  
  Notice how with the -R option, the listing shows the contents of the two subdirectories.
  
  

  Figure 5.17. Using the -R option tells ls that you want a recursive directory listing.

   localhost:~/Public vanilla$  ls ~/Sites  images                index.html         test localhost:~/Public vanilla$  ls -R   ~/Sites  images                index.html         test /Users/vanilla/Sites/images: apache_pb.gif         macosxlogo.gif     web_share.gif localhost:~/Public vanilla$