sed

Regular expressions.

• Replace the first occurrence of a string in a file, and print the result:

  sed 's/find/replace/' filename
  

• Replace only on lines matching the line pattern:

  sed '/line_pattern/s/find/replace/'
  

• Replace all occurrences of a string in a file, overwriting the file (i.e. in-place):

  sed -i 's/find/replace/g' filename
  

• Replace all occurrences of an extended regular expression in a file:

  sed -r 's/regex/replace/g' filename
  

• Apply multiple find-replace expressions to a file:

  sed -e 's/find/replace/' -e 's/find/replace/' filename
  

File spacing

• double space a file

  sed G
  

• double space a file which already has blank lines in it. Output file should contain no more than one blank line between lines of text.

  sed '/^$/d;G'
  

• triple space a file

  sed 'G;G'
  

• undo double-spacing (assumes even-numbered lines are always blank)

  sed 'n;d'
  

• insert a blank line above every line which matches “regex”

  sed '/regex/{x;p;x;}'
  

• insert a blank line below every line which matches “regex”

  sed '/regex/G'
  

• insert a blank line above and below every line which matches “regex”

  sed '/regex/{x;p;x;G;}'
  

Userful

• List out the second column in the table.

  cat text/table.txt | sed 1d | awk '{ print $2 }'
  

• Sum the columns in the table.

  cat text/table.txt | sed 1d | awk '{ sum += $2 } END { print sum }'
  

• Kills all processes by name.

  ps aux | grep chrome | awk '{ print $2 }' | kill (or) pkill chrome
  

• Deletes trailing whitespace.

  sed 's/\s\+$//g' filename
  

• Deletes all blank lines from file.

  sed '/^$/d' filename
  

• Insert ‘use strict’ to the top of every js file.

  sed "1i 'use strict';" *.js
  

• Append a new line at the end of every file.

  sed '1a \n' *
  

• Generate random numbers and then sort.

  for i in {1..20}; do echo $(($RANDOM * 777 * $i)); done | sort -n
  

• Commatize numbers.

  sed -r ':loop; s/(.*[0-9])([0-9]{3})/\1,\2/; t loop' text/numbers.txt
  

Sed Print

• Print contents of a file.

  sed -n '/fox/p' text/* (or) sed -n '/Sysadmin/p' text/geek.txt
  

• Print lines starting with 3 and skipping by 2.

  sed -n '3~2p' text/geek.txt
  

• Print the last line.

  sed -n '$p' text/geek.txt
  

• Prints the lines matching the between the two patterns.

  sed -n '/Hardware/,/Website/p' text/geek.txt
  

  Sed Print Number

• Prints the line number for all lines in the file.

  sed -n '=' filename
  

• Prints the line number that matches the pattern.

  sed -n '/Linux/=' filename
  

• Prints the line number in range of two patterns (inclusive).

  sed -n '/Linux/,/Hardware/=' filename
  

• Prints the total number of lines.

  sed -n '$=' filename
  

• number each line of a file (simple left alignment). Using a tab (see note on ‘\t’ at end of file) instead of space will preserve margins.

  sed = filename | sed 'N;s/\n/\t/'
  

• number each line of a file (number on left, right-aligned)

  sed = filename | sed 'N; s/^/     /; s/ *\(.\{6,\}\)\n/\1  /'
  

• number each line of file, but only print numbers if line is not blank

  sed '/./=' filename | sed '/./N; s/\n/ /'
  

• count lines (emulates “wc -l”)

  sed -n '$='
  

Sed Delete

The d command performs a deletion.

• Deletes the 3rd line from beginning of file.

  sed '3d' text/geek.txt
  

• Delete every lines starting from 3 and skipping by 2.

  sed '3~2d' text/geek.txt
  

• Delete lines from 3 to 5.

  sed '3,5d' text/geek.txt
  

• Delete the last line.

  sed '$d' text/geek.txt
  

• Delete lines matching the pattern.

  sed '/Sysadmin/d' text/geek.txt
  

• delete lines matching pattern

   sed '/pattern/d'
  

• delete ALL blank lines from a file (same as “grep ‘.’ “)

   sed '/^$/d'                           # method 1
   sed '/./!d'                           # method 2
  

  Sed Substitute

  The s command performs a substitution.

• Simple substituion for the first result.

  sed 's/Linux/Unix/' text/geek.txt
  

• Simple substituion for global instances.

  sed 's/Linux/Unix/g' text/geek.txt
  

• Replace nth instance.

  sed 's/Linux/Unix/2' text/geek.txt
  

• Write matched lines to output.

  sed -n 's/Linux/Unix/gp' text/geek.txt > text/geek-sub.txt
  

• Use regex group for capturing additional patterns (up to 9).

  sed 's/\(Linux\).\+/\1/g' text/geek.txt
  

  sed -r 's/(Linux).+/\1/g' text/geek.txt
  

• Remove the last word.

  sed -r 's/\d$//g' text/geek.txt
  

• Remove all letters.

  sed -r 's/[a-zA-Z]//g' text/geek.txt
  

• Remove html tags (WIP).

  sed -r 's|(</?[a-z]+>)||g' text/html.txt
  

• Commatize any number.

  sed ':a;s/\B[0-9]\{3\}\>/,&/;ta' text/numbers.txt
  

  sed -r ':loop; s/\B[0-9]{3}\>/,&/; t loop' text/numbers.txt
  

Sed Transform

The y command performs a transformation.

• Converts all lowercase chars to uppercase.

  sed 'y/abcdefghijklmnopqrstuvwxyz/ABCDEFGHIJKLMNOPQRSTUVWXYZ/' text/geek.txt
  

• Converts all uppercase chars to lowercase.

  sed 'y/ABCDEFGHIJKLMNOPQRSTUVWXYZ/abcdefghijklmnopqrstuvwxyz/' text/geek.txt
  

• Perform a two character shift.

  sed 'y/abcdefghijklmnopqrstuvwxyz/cdefghijklmnopqrstuvwxyzab/' text/geek.txt
  

Special appplicatoins

• get Usenet/e-mail message header

  sed '/^$/q'                # deletes everything after first blank line
  

• get Usenet/e-mail message body

  sed '1,/^$/d'              # deletes everything up to first blank line
  

• get Subject header, but remove initial “Subject: “ portion

  sed '/^Subject: */!d; s///;q'
  

• get return address header

  sed '/^Reply-To:/q; /^From:/h; /./d;g;q'
  

Sed Multiple Commands

• The -e flag allows for multiple commands.

  sed -r -e 's/etc\.*//g' -e 's/(\s+)(\))/\2/g' text/geek.tx