CPS 250, 346, & 444/544 Lecture notes: Files & directories
(manipulation & management)
Coverage: [UPE] Chapters 2 and Chapter 7 (pp. 201-202)
Basic UNIX file nomenclature
- absolute or fully qualified path vs. relative path
- current working directory (stored in PWD variable)
- . and .. (are not shell metacharacters)
- types of files
- see man ls
- ls -l
b block special file c character special file d directory l symbolic link s socket link p FIFO - regular file
ls and cal
- ls [<dir(s)/file(s)>] (list): list directory contents; without a directory argument defaults to the current directory, as do most UNIX commands ls with file arguments lists information about only those files
- ls -a [<dir(s)/file(s)>] (all): list directory contents including hidden (dot) files; also lists hidden (dot) files, which are typically configuration files (e.g., .profile)
- ls -l [<dir(s)/file(s)>]
(long listing): list directory contents using long listing format;
explanation of fields
- file permission string (-rwx------)
- owner, group, other
- ls -al
- ls -F [<dir(s)/file(s)>] (fancy): list directory contents following directories with a slash, executable files with an asterisk, links with a @, including other various decorations; fancier output
- ls -ld <dir>: lists details of actual directory, rather than its contents
- cal
- cal 9 (print calendar for year 9, not Sep, current year)
- cal 2004
- cal 9 1752
Explanation of ls -l output
-
example:
total 6 drwxr-xr-x 6 lucy cps444 480 Dec 6 17:42 . drwxr-xr-x 26 root system 816 Dec 6 14:45 .. drwxr-xr-x 2 lucy cps444 80 Oct 25 08:33 bin drwx------ 2 lucy cps444 144 Nov 30 14:25 C -rw-rw-r-- 1 lucy cps444 104 Sep 12 19:54 notes -rwxrwxr-- 1 lucy cps444 85 Jan 4 20:06 run* drw-rw-rw- 2 lucy cps444 32 Mar 23 13:45 memos drwx------ 16 lucy cps444 1296 Dec 6 17:33 text
UNIX filesystem
- directories (branches) contain either files or subdirectories (branches of branches)
- the filesystem is usually viewed as an inverted (upside
down) tree
- highest level directory = root /
- user's current directory is known as the working directory
- all of the following directories are owned by user root (system administrator)
- /tmp (temporary files); need not have special privileges to write here
- /bin (binaries, executables)
- /sbin
- /src (source code)
- /usr
- /usr/src
- /usr/src/lib
- /usr/bin
- /usr/include ← contains stdio.h and string.h
- /usr/lib
- /usr/lib64 ← contains libc.a
- /home (user home directories)
- /lib (libraries)
- /lib64 (libraries) ← contains libc.so.6
- /etc (configuration files)
- /dev (devices)
- /dev/null (system trashcan)
- hier (only on some systems)
- tree (only on some systems)
Absolute vs. relative path
- pathname: filename preceded by directories leading to the file
- absolute pathname: the complete pathname of a file
starting with the root /
(e.g., /home/cps444-n1.01/homeworks/hw1/wc.c)
- relative pathname: pathname which implicitly starts at the
working directory (e.g., homeworks/hw1/wc.c)
Two special files in every directory
- . and ..
- . is a link to the current working directory
- .. is a link to the directory containing the current working directory (i.e., its parent)
- why do we need these?
Navigating through directories
(below pathnames to <file>
or <dir> can be absolute or relative)
- cd <dir> (change directory): change directory to <dir> alters working directory; used to traverse UNIX hierarchical tree file structure
- cd: change to home directory
- cd ..: changes to parent directory of working directory
- cd ~<logname>: change to home directory of user with login name <logname>
- cd ~-: change to previous working directory
File manipulation and management
- pwd: print working directory; displays current working directory path
- cp <src> <dest>: copy file(s)
- for instance, cp ../hw1/wc.c wc.bak: creates a separate file wc.bak; changes made to one do not affect the other
- for instance, $ cp ../hw1/* .; copies all files from parent/hw1 to the current directory
- rm <file(s)> (remove): erases file(s)
- be careful, no undelete, no training wheels
- does not notify user of the action that has occurred
- rm accepts a list of files to erase
- for instance, rm *.c erases all of the C files,
- whereas rm * erases all of the files in the working directory
- rm -i wc.c: forces rm to query before erasing files
- interactive
- adds confirmation (training wheels)
- for instance, rm -i ../hw1/wc.c
- some like alias rm="rm -i"
- mkdir <dir(s)> (make directory): creates one or more directories
- rmdir <dir(s)> (remove directory): deletes one or more directories which must be empty
- rm -r <file(s)/dir(s)>
- use with extreme caution
- directory need not be empty
- mv <src> <dest> (move):
relocates the file(s) into the specified directory
- for instance, mv wc.c ../backups/
- mv is also used to rename a file leaving the location unaltered (e.g., mv wc.c wc1.c)
- more <file(s)> (or page): display <file(s)> one screen at a time; use spacebar to page through
- less <file(s)>:
displays/browse file(s) one screen at a time, move
forward or backward through file, and can search for patterns (unlike more,
browsing begins before entire file loaded into memory)
- spacebar pages through
- enter key scrolls down a line
- searchable through /<keyword>; n moves cursor to next match
- hit q key to quite
- head, tail: can specify number of lines with option
- lpr <file(s)> (line printer): prints one or more files on the default printer
- pushd and popd
References
| [C] | C Language for Experienced Programmers, Version 2.0.0, AT&T, 1988. |
| [UPE] | B.W. Kernighan and R. Pike. The UNIX Programming Environment. Prentice Hall, Upper Saddle River, NJ, Second edition, 1984. |
