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Chapter 13: sed

Chapter 13: sed. Say what?. In this chapter …. Basics Programs Addresses Instructions Control Spaces Examples. sed. GNU sed (stream editor) Noninteractive, batch editing Good for repetitive tasks Often used in a pipe. sed syntax. Syntax: sed [ options ] program [ filelist ]

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Chapter 13: sed

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  1. Chapter 13:sed Say what?

  2. In this chapter … • Basics • Programs • Addresses • Instructions • Control • Spaces • Examples

  3. sed • GNU sed (stream editor) • Noninteractive, batch editing • Good for repetitive tasks • Often used in a pipe

  4. sed syntax • Syntax: sed [options] program [filelist] sed [options] program-file [filelist] • Program is a set of commands for editing • Can either be issued on the command line or placed into a file (like gawk) • Filelist is a list files to edit • If omitted, input taken from standard in

  5. sed syntax con’t • Options --in-place[=suffix] • Instead of sending edited text to standard out, write changes back to input file • Adding =suffix makes backup of original file -n • Do not send lines to output unless program explicitly says to

  6. Programs • sed programs contain one or more lines with the following syntax: [address[,address]] instruction [args] • Simple one or two line programs can be issued at the command line • More complex programs are usually best put in a program file

  7. How sed works • Read one line of input • Read first instruction in program. If the address(es) select this line, runs the instruction on this line • Repeat #2 for each line in the program • Read next line of input and go back to step 2, until there are no more lines of input

  8. Addresses • Select which lines are to be processed • Can be a simple integer (line number) or a regular expression (pattern matching) • Address $ represents last line of input • If address omitted, all lines processed by default • If there is one address, only lines that match will be processed

  9. Addresses con’t • If two addresses are given, it selects a range • Once the first address is matched, it and subsequent lines are processed until the second address is matched • If second address is never matched, processes remainder of lines • If second addressed matched, sed will then try to match first address again

  10. Instructions • d – does not write out (deletes) selected line and does not process line any further • n – writes out current line, reads next line, and processes next program line • a – appends lines after current line • i – inserts lines before current line • c – changes select line so it contains new text • p – print current line (override –n)

  11. Instructions con’t • w file – write line to a specified file • r file – read contents of file and appends to current line • q – quits sed immediately

  12. Instructions con’t • s/pattern/replacement-str/[g][p][w file] • Substitutes first occurrence of pattern with replacement-str • g replaces all occurences • p prints changed line • w writes changed line to file • Use & to represent the pattern matched when replacing • Ex. s/a.*/(a.*)/ won’t work … instead use s/a.*/(&)/

  13. Control Structures • ! (NOT) – causes instruction to be performed on all lines not selected by address(es) • { } (Instruction grouping) – causes multiple instructions to be run on one address / address pair; separate with semicolons • : label – identify a location in a sed program • b label – branch to label • t label – conditionally branch to label if last Substitute instruction was successful

  14. Spaces • sed has two spaces (buffers) • Think of them like vim’s buffers • Lines read from input are put in patternspace • You can also move data back and forth from the hold space (temporary buffer)

  15. Spaces, cont • g – overwrites pattern space with hold space • G – appends hold space to pattern space • h – overwrites hold space with pattern space • H – appends pattern space to hold space • x – swaps the pattern and hold spaces

  16. Examples • sed -n‘/line/ p’ myfile • Prints out lines in myfile that contain ‘line’ • sed ‘2,4 d’ myfile • Delete lines 2-4, outputs remaining • sed --in-place ‘2,4 d’ myfile • Deletes lines 2-4 from myfile • sed ‘s/tea/coffee/g’ myfile • Replaces tea with coffee and prints to screen

  17. More Examples • sed ‘5 q’ myfile • Prints first five lines then quits ( equiv. head -5) • sed ‘/^[0-9]/ w newfile’ myfile • Copies lines starting in number to newfile • sed ‘$ r newfile’ myfile • Appends contents of newfile to end of myfile • sed ‘G’ myfile • What does this do?

  18. Program File Example 1 d s/company/Company/g $ a\ Revised 12-1-2005\ by JMH $ d

  19. Another Program File 1 i \ \ Manuf\tModel\tYear\tMiles\tPrice\ ===================================== s/thundbd/tbird/g s/.*/ &/ $ a \ =====================================

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