1 / 16

Lecture 7.1

Lecture 7.1. Sed. sed. sed is a stream-oriented editor the input (file/ std input) flows through the program sed and is directed the standard output Used primarily for non interactive operations sed [-n] –f script_file file or sed [-n] command file

tariq
Download Presentation

Lecture 7.1

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 7.1 Sed

  2. sed • sed is a stream-oriented editor • the input (file/std input) flows through the program sed and is directed the standard output • Used primarily for non interactive operations • sed [-n] –f script_file file or sed [-n] command file • sed executes the given command or script file that contain commands on each line of the input (file) • -n: turn off default printing

  3. sed Commands • p: print line • -nprevents lines from being printed twice • d: delete line • s: substitution • s/old/new/: substitute old with new • s/old/new/g: substitute all occurrences of old with new • !: negates a command

  4. sed Examples • sed p file.txt (print each line twice) • sed –n p file.txt • sed d file.txt (print nothing) • sed \!d file.txt (print each line) • p and d seem a bit worthless, don’t they? They purpose will become more clear when we discuss addresses.

  5. sed: Substitution • The strongest feature of sed • Syntax is s/expression/string/flag • expression is a regular expression • string is a string • sed ‘s/:/|/’ /etc/passwd • substitute the character ‘|’ with the character ‘:’ • sed ‘s/:/|/g’ /etc/passwd • apply to all matches in the line

  6. Some Useful Substitution Flags • g: global (replace all matches on the line). • p: print the line if a successful match • sed –n ‘s/old/new/g’ file.txt • sed ‘s/old/new/gp’ file.txt • sed –n ‘s/old/new/gp’ file.txt

  7. Regular Expressions for sed • The usual R.E. operators • ^, $, ., *, [ ], [^ ], \( \), \<, \>, • A new operator • &: the string which matches the expression • can be used in the substitution string • s/hello/**&**/g replaces all occurrences of hello with **hello**

  8. sed Addressing • So far, we have been applying sed commands to every line • makes p and d not very useful • With addressing, we can apply commands to some, but not all lines • sed can use • 0 addresses (all lines) • 1 address (a single line) • 2 addresses (a range of lines) • Address can be line numbers of context (defined by regular expressions)

  9. Line Number Addressing Examples %sed –n ‘3,4p’ foo.txt Since sed prints each line anyway, if we only want lines 3 & 4 (instead of all lines with lines 3 & 4 duplicated) we use the –n %sed –n ‘$p’ foo.txt # $=last line For each line, if that line is the last line, print %sed –n ‘3,$p’ foo.txt For each line, if that line is the third through last line, print

  10. Context Addressing Examples • Use patterns/regular expressions rather than explicitly specifying line numbers %sed –n ‘/^From: /p’ $HOME/mbox • retrieve all the sender lines from the mailbox file, i.e., for each line, if that line starts with ‘From’, print it. Note that the / / mark the beginning and end of the pattern to match %ls –l | sed –n ‘/^.....w/p’ • For each line, if the sixth character is a W, print

  11. Context Ranges • sed ‘/hello/,/there/d’ file.txt • delete all lines that occur between a line that matches hello and a line that matches there. The hello and there lines are also removed. • Multiple contexts are possible • sed ‘/hello/,/there/d; /if/,/end/d’ file.txt

  12. Example file northwest NW Charles Main 3.0 .98 3 34 western WE Sharon Gray 5.3 .97 5 23 southwest SW Lewis Dalsass 2.7 .8 2 18 southern SO Suan Chin 5.1 .95 4 15 southeast SE Patricia Heme 4.0 .7 4 17 eastern EA TB Savage 4.4 .84 5 20 northeast NE AM Main Jr. 5.1 .94 3 13 north NO Margot Webber 4.5 .89 5 9 central CT Ann Stephens 5.7 .94 5 13 sed ‘/north/p’ file sed -n ‘s/west/north/g’ file (no print out, need a p) sed ‘3,$d’ file sed ‘s/\(Mar\)got/\1ianne/p’ file sed ‘s/west/north/g’ file sed ‘/west/,/east/s/$/**VACA**/’ file

  13. sed: Using files • Tedious to type in commands at the prompt, especially if commands are repetitive • Can put commands in a file and sed can use them • sed –f cmds.sed data.txt file with commands

  14. sed scripts • Series of commands can be put in a file and use the ‘-f’ option. • Can also create an sed script: s/vi/emacs/g /[Ww]indows/d p

  15. Another Example • sed script to remove all HTML tags from a file: s/<[^>]*>//g p

  16. Announce Lab 3 http://www.cse.ohio-state.edu/~lido/teaching/sp2013cse4251/lab3.html

More Related