CSCI 2132 Software Development Lecture 7: Wildcards and Regular - - PowerPoint PPT Presentation

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CSCI 2132 Software Development Lecture 7: Wildcards and Regular - - PowerPoint PPT Presentation

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CSCI 2132 Software Development Lecture 7: Wildcards and Regular Expressions Instructor: Vlado Keselj Faculty of Computer Science Dalhousie University 19-Sep-2018 (7) CSCI 2132 1 Previous Lecture Pipes Inodes Hard links Soft

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CSCI 2132 Software Development Lecture 7: Wildcards and Regular Expressions

Instructor: Vlado Keselj Faculty of Computer Science Dalhousie University

19-Sep-2018 (7) CSCI 2132 1

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Previous Lecture

  • Pipes
  • Inodes
  • Hard links
  • Soft links
  • Filename Substitution (Wildcards) (started)

19-Sep-2018 (7) CSCI 2132 2

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Filename Substitution (Wildcards)

  • Also known as pathname substitution
  • Used to specify multiple filenames (i.e., pathnames)
  • Makes use of “wildcards”; i.e., metacharacters expanded

by the shell

  • Some wildcard types:

– ?: matches any single character – *: matches any string, including empty string – [...]: matches any single character in the set – [!...]: any character except characters from the set – we can use ranges with ‘-’ in brackets

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File Substitution Examples

  • [0-9]

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File Substitution Examples

  • [0-9]: any digit between 0 and 9

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File Substitution Examples

  • [0-9]: any digit between 0 and 9
  • [a-zA-Z]

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File Substitution Examples

  • [0-9]: any digit between 0 and 9
  • [a-zA-Z]: any English alphabet character

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File Substitution Examples

  • [0-9]: any digit between 0 and 9
  • [a-zA-Z]: any English alphabet character
  • [unix]

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File Substitution Examples

  • [0-9]: any digit between 0 and 9
  • [a-zA-Z]: any English alphabet character
  • [unix]: matches either ‘u’, ‘n’, ‘i’, or ‘x’

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File Substitution Examples

  • [0-9]: any digit between 0 and 9
  • [a-zA-Z]: any English alphabet character
  • [unix]: matches either ‘u’, ‘n’, ‘i’, or ‘x’
  • ls ˜/csci2132/lab1/*.java

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File Substitution Examples

  • [0-9]: any digit between 0 and 9
  • [a-zA-Z]: any English alphabet character
  • [unix]: matches either ‘u’, ‘n’, ‘i’, or ‘x’
  • ls ˜/csci2132/lab1/*.java — list Java files

19-Sep-2018 (7) CSCI 2132 11

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File Substitution Examples

  • [0-9]: any digit between 0 and 9
  • [a-zA-Z]: any English alphabet character
  • [unix]: matches either ‘u’, ‘n’, ‘i’, or ‘x’
  • ls ˜/csci2132/lab1/*.java — list Java files
  • ls *.????

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File Substitution Examples

  • [0-9]: any digit between 0 and 9
  • [a-zA-Z]: any English alphabet character
  • [unix]: matches either ‘u’, ‘n’, ‘i’, or ‘x’
  • ls ˜/csci2132/lab1/*.java — list Java files
  • ls *.???? — list all files with 4-character extension

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File Substitution Examples

  • [0-9]: any digit between 0 and 9
  • [a-zA-Z]: any English alphabet character
  • [unix]: matches either ‘u’, ‘n’, ‘i’, or ‘x’
  • ls ˜/csci2132/lab1/*.java — list Java files
  • ls *.???? — list all files with 4-character extension
  • ls lab[1-9]

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File Substitution Examples

  • [0-9]: any digit between 0 and 9
  • [a-zA-Z]: any English alphabet character
  • [unix]: matches either ‘u’, ‘n’, ‘i’, or ‘x’
  • ls ˜/csci2132/lab1/*.java — list Java files
  • ls *.???? — list all files with 4-character extension
  • ls lab[1-9] — list all files with the name consisting of

word lab and a digit from 1 to 9

19-Sep-2018 (7) CSCI 2132 15

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File Substitution Examples

  • [0-9]: any digit between 0 and 9
  • [a-zA-Z]: any English alphabet character
  • [unix]: matches either ‘u’, ‘n’, ‘i’, or ‘x’
  • ls ˜/csci2132/lab1/*.java — list Java files
  • ls *.???? — list all files with 4-character extension
  • ls lab[1-9] — list all files with the name consisting of

word lab and a digit from 1 to 9

  • ls [!0-9]*

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File Substitution Examples

  • [0-9]: any digit between 0 and 9
  • [a-zA-Z]: any English alphabet character
  • [unix]: matches either ‘u’, ‘n’, ‘i’, or ‘x’
  • ls ˜/csci2132/lab1/*.java — list Java files
  • ls *.???? — list all files with 4-character extension
  • ls lab[1-9] — list all files with the name consisting of

word lab and a digit from 1 to 9

  • ls [!0-9]* — list all files which name does not start

with a digit

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File Substitution Examples

  • [0-9]: any digit between 0 and 9
  • [a-zA-Z]: any English alphabet character
  • [unix]: matches either ‘u’, ‘n’, ‘i’, or ‘x’
  • ls ˜/csci2132/lab1/*.java — list Java files
  • ls *.???? — list all files with 4-character extension
  • ls lab[1-9] — list all files with the name consisting of

word lab and a digit from 1 to 9

  • ls [!0-9]* — list all files which name does not start

with a digit

  • cp lab1.bk/*.java lab1/

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File Substitution Examples

  • [0-9]: any digit between 0 and 9
  • [a-zA-Z]: any English alphabet character
  • [unix]: matches either ‘u’, ‘n’, ‘i’, or ‘x’
  • ls ˜/csci2132/lab1/*.java — list Java files
  • ls *.???? — list all files with 4-character extension
  • ls lab[1-9] — list all files with the name consisting of

word lab and a digit from 1 to 9

  • ls [!0-9]* — list all files which name does not start

with a digit

  • cp lab1.bk/*.java lab1/ — copy Java files from
  • ne directory to another

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More Examples

  • ls ˜/csci2132/lab1/*.java
  • ls ˜/csci2132/lab1/H????World.java
  • ls H*
  • ls [!A-Z]*
  • ls */*/*.java
  • ls *.java */*.java
  • echo .*
  • command echo — prints out command line arguments
  • cat *.txt > allfiles

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Regular Expressions

  • Regular Expressions are patterns used to match strings, and thus

used in fast and flexible text search

  • The name comes from Regular Sets defined by the mathematician

Stephen Kleene

  • Implemented as DFA (Deterministic Finite Automata) or NFA

(Non-deterministic Finite Automata)

  • Kleene’s notation implemented by Ken Thompson into the editor

QED to match patterns

  • Thompson later added this to the Unix editor ed
  • Eventually led to the command grep, coming from ed command

g/re/p (Global search for Regular Expression and Print matching lines)

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Reading about Regular Expressions

  • The Unix book: Chapter 3, Filtering Files (p.84)
  • Appendix: Regular Expressions (p.665)
  • Regular expressions

– Patterns used for searching and replacing text – Used in many contexts, but we will focus on the grep command – There are two kinds of regular expressions: basic regular expressions and extended regular expressions

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Basic Regular Expressions

  • Using metacharacters:
  • .: Matches any single character
  • [...]: Matches any character between brackets, -

used to specify range; most other metacharacters loose their “meta-meaning” between brackets

  • [ˆ...]: Matches any character except one of the

characters between brackets

  • *: 0 or more occurrences of the preceding character
  • ˆ: Matches the beginning of a line
  • $: Matches the end of a line
  • \: Inhibits the meaning of any metacharacter

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BRE Examples

  • BRE = Basic Regular Expressions
  • One or more spaces: spacespace* (replace space by a

space character): ‘ *’

  • Empty line: ˆ$
  • Formatted dollar amount:

\$[0-9][0-9]*\.[0-9][0-9]

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Filters, grep command

  • Filter is a program that is mostly used to read stdin,

process data, and write to stdout

  • Often used as elements of pipelines
  • One such program is grep
  • grep reads a file or stdin and outputs lines matching a

regular expression

  • grep syntax

grep [options] BRE [file(s)]

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Example

Chocolate $1.23 each Candy $.56 each Jacket $278.00</pre> <pre>$44.00 $44 If we enter the following command grep ’\$[0-9][0-9]*\.[0-9][0-9]’ price The output will be the following three lines: Chocolate $1.23 each Jacket $278.00 $44.00

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One more grep example

  • We will use the dictionary file:

/usr/share/dict/linux.words

  • Write a grep command to find 5-letter words that start

with ‘a’ or ‘b’ and end with ‘b’

  • Write a grep command to find all words starting with ‘a’
  • r ‘b’ and ending with ‘b’
  • How many are there?

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Similarity between Wildcards and Regular Expressions

  • We can get similar results with wildcards and regular

expressions; e.g.: ls *.java ls | grep ’\.java$’

  • List of all files in /bin, whose names contain exactly
  • ne minus sign (-):

ls /bin | grep ’ˆ[ˆ-]*-[ˆ-]*$’

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