Mercurial > docs > unix-phil

comparison unix-phil.ms @ 4:c707b0c5c849

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
new text about pipes
author meillo@marmaro.de
date Fri, 12 Feb 2010 19:30:13 +0100
parents aebbe3e76f5e
children 48f1f3465550
comparison
equal deleted inserted replaced
3:aebbe3e76f5e 4:c707b0c5c849
164 164
165 165
166 166
167 .NH 1 167 .NH 1
168 The Unix Philosophy 168 The Unix Philosophy
169 169 .LP
170 .NH 2 170 The origins of the Unix Philosophy were already introduced.
171 what it is 171 This chapter explains the philosophy and shows concrete examples of its application.
172 .LP 172 .NH 2
173 definitions by McIlroy, Gancarz, ESR (maybe already in the intro) 173 Examples
174 .LP 174 .LP
175 cf. unix tool chain 175 Following are some examples to demonstrate how applied Unix Philosophy feels like.
176 .LP 176 Knowledge of using the Unix shell is assumed.
177 enabler pipe 177 .PP
178 Counting the number of files in the current directory:
179 .DS
180 .CW
181 ls | wc -l
182 .DE
183 The
184 .CW ls
185 command lists all files in the current directory, one per line,
186 and
187 .CW "wc -l
188 counts how many lines they are.
189 .PP
190 Counting all files that do not contain ``foo'' in their name:
191 .DS
192 .CW
193 ls | grep -v foo | wc -l
194 .DE
195 Here, the list of files is filtered by
196 .CW grep
197 to remove all that contain ``foo''.
198 The rest is the same as in the previous example.
199 .PP
200 Finding the five largest entries in the current directory.
201 .DS
202 .CW
203 du -s * | sort -nr | sed 5q
204 .DE
205 .CW "du -s *
206 returns the recursively summed sizes of all files
207 -- no matter if they are regular files or directories.
208 .CW "sort -nr
209 sorts the list numerically in reverse order.
210 Finally,
211 .CW "sed 5q
212 quits after it has printed the fifth line.
213 .PP
214 The presented command lines are examples of what Unix people would use
215 to get the desired output.
216 There are also other ways to get the same output.
217 It's a user's decision which way to go.
218 .NH 2
219 Pipes
220 .LP
221 The examples show that a lot of tasks on a Unix system
222 are accomplished by combining several small programs.
223 The connection between the single programs is denoted by the pipe operator `|'.
224 .PP
225 Pipes, and their extensive and easy use, are one of the great
226 achievements of the Unix system.
227 Pipes between programs have been possible in earlier operating systems,
228 but it has never been a so central part of the concept.
229 When, in the early seventies, Doug McIlroy introduced pipes for the
230 Unix system,
231 ``it was this concept and notation for linking several programs together
232 that transformed Unix from a basic file-sharing system to an entirely new way of computing.''
233 .[
234 %T Unix: An Oral History
235 %O http://www.princeton.edu/~hos/frs122/unixhist/finalhis.htm
236 .]
237 .PP
238 Being able to specify pipelines in an easy way is,
239 however, not enough by itself.
240 It is only one part.
241 The other is the design of the programs that are used in the pipeline.
242 They have to be of an external shape that allows them to be be used in a pipeline.
243
244
178 245
179 .NH 2 246 .NH 2
180 Architecture 247 Architecture
181 .LP 248 .LP
182 the most important design decision. 249 the most important design decision.