CIS241

System-Level Programming and Utilities

Stream Editor (sed)

Erik Fredericks, frederer@gvsu.edu
Fall 2025

Based on material provided by Erin Carrier, Austin Ferguson, and Katherine Bowers

sed

Manipulates input (stream or file)

Typically:

• sed [options] '/pattern/ command' input_file
• sed [options] 'range command' input_file

Common options

-E to use extended regex

-f filename to load sed commands from a file

--in-place or -i to modify a file in place

• --in-place=suffix or -isuffix to create a backup file with suffix extension

Stream manipulation - Deleting lines:

• sed '4 d'
• sed '1,4 d'
• sed -E '/pattern/ d'

($ is the end of file when using ranges!)

Stream manipulation - substituting text:

• sed -E 's/pattern/replace_str'
  • Ex: sed -E 's/ *$//' filename

By default, only replaces first match per line

• Replace all: sed -E 's/pattern/replace_str/g'
• Replace second: sed -E 's/pattern/replace_str/2'

Can combine patterns with ranges!

• sed -E '5,$ s/pattern/replace_str/'

Stream manipulation - substituting text:

• sed -E 's/pattern/replace_str'

Can also use parts of matched pattern in replacement!

• Uses (parentheses groupings)

• To refer to parentheses groups: \1, \2, ...

  • sed -E 's/the ([[:alpha:]]+) /\1/

• To refer to the whole matched pattern: &

  • sed -E 's/(.+\.com)/www.&/'

  https://www.geeksforgeeks.org/linux-unix/sed-command-in-linux-unix-with-examples/