CS 497C - Introduction to UNIX
Lecture 23: - Simple Filters
Chin-Chih Chang chang@cs.twsu.edu

more: Paging Output
* UNIX offers two pagers: more and less.
* To view the file chap1, use more chap1.
* more is a pager that shows output of a file at a time.
* You can scroll both forward (f) and backward (b).
* You can search for a pattern (/pattern). The pattern can be both a simple 
  string as well as a regular expression.
/[sS]ystem matches two strings.

more: Paging Output
* /^# matches the line beginning with #.
* You can repeat the last command with a dot.
* You can switch to the next file (n) or previous file (p) with multiple 
  files.
* more is often used in a pipeline such as:
ls -l | more
* You can use the help facility by hitting h.
* You can also invoke the vi editor directly from the pager (v).

wc: Line, Word and Character Counting
* wc counts the number of lines, words and characters.
* You can use wc with options to specify count. The -l option counts only 
  the number of line. The -w and -c options count words and characters 
  respectively.
* When used with multiple files, it prints a total of everything.
* wc can be used a filter to count lines and words in the standard output.

od: Displaying Data in Octal
* od displays the octal value of a character, and is used to display 
  invisible characters.
* When used with the -bc options, it shows you the escape sequences \f 
  (formfeed), \n (newline), and \t (tab).
od -bc odfile
* You can use od to find out the nonpritable character in the filename.
ls P* | od -bc

pr: Paginating Files
* The pr command prepares a file for printing by adding suitable headers, 
  footers, and formatted text.
* It is mostly used in conjunction with the lpr (lp) command.
pr program.c | lpr
* The -l (length) option is used to specify a different page size.

pr: Paginating Files
* The output can be double-spaced (-d), printed in multiple columns (-k), and
  set to start from a specific page number (+k).
* The -t option removes all headers.
* The following command format output in two columns without any header.
pr -t -2 group

cmp: Comparing Two Files
* There are three file comparison utilities in the UNIX system: cmp, diff, 
  and comm. 
* The cmp (compare) command tells you where the first difference was 
  encountered. 
* The -l (list) option gives a detailed character-for-character listing.
* You can use cmp in a pipeline to count the number of differences between 
  two files:
cmp -l group? | wc -l

diff: Converting one File to Another
* The diff command shows the differing lines, using a set of instructions 
  which, when applied to one file, converts it to the other.
* Each instruction is applied to the first file and comprises an address and 
  an action.
* The instruction 3c3 indicates the change of line 3 in both files. 7a8 
  means appending a line after 7, yielding line 8 in the second file. 5, 6c 
  changes two lines.