# sed — Stream Editor for Text Transformation > Filter and transform text with sed — substitution, in-place editing, line addressing, deletion and back-references for scripts and pipelines. Source: https://www.jpkc.com/db/en/cheatsheets/files-text/sed/ sed (stream editor) reads text line by line and applies editing commands as the data flows through – no interactive editor, no temp files. Its bread and butter is search-and-replace with `s/pattern/replacement/`, but it also deletes, inserts, prints and reorders lines, addressed by number or by regex. You will reach for it whenever you need to patch config files, rewrite URLs, strip whitespace or massage command output in a pipeline. This guide walks from basic substitution through in-place editing, line addressing and back-references to the recipes you actually use. ## Basic Substitution `sed 's///' ` — Replace the first occurrence of pattern on each line. ```bash sed 's/foo/bar/' input.txt ``` `sed 's///g' ` — Replace all occurrences of pattern on each line (global). ```bash sed 's/foo/bar/g' input.txt ``` `sed 's///gi' ` — Replace all occurrences, case-insensitive. ```bash sed 's/error/warning/gi' log.txt ``` `sed 's///2' ` — Replace only the Nth occurrence of pattern on each line. ```bash sed 's/the/THE/2' input.txt ``` `sed 's///gp' ` — Replace globally and print only the changed lines (use with -n). ```bash sed -n 's/error/ERROR/gp' log.txt ``` ## In-Place Editing `sed -i 's///g' ` — Edit the file in-place (modifies the original file directly). ```bash sed -i 's/localhost/production.example.com/g' config.yml ``` `sed -i.bak 's///g' ` — Edit in-place and create a backup with the given suffix. ```bash sed -i.bak 's/debug=true/debug=false/g' config.ini ``` `sed -i '' 's///g' ` — Edit in-place without backup (macOS/BSD syntax, empty suffix required). ```bash sed -i '' 's/old/new/g' config.yml ``` `sed -i 's///g' ` — Edit multiple files in-place with the same substitution. ```bash sed -i 's/v1.0/v2.0/g' README.md CHANGELOG.md ``` ## Delimiters & Special Characters `sed 's|||g' ` — Use | as delimiter instead of /. Useful when patterns contain slashes. ```bash sed 's|/usr/local|/opt|g' paths.conf ``` `sed 's###g' ` — Use # as delimiter. Any character can serve as delimiter. ```bash sed 's#http://#https://#g' urls.txt ``` `sed 's/[[:space:]]*$//' ` — Remove trailing whitespace from each line. ```bash sed 's/[[:space:]]*$//' source.py ``` `sed 's/^[[:space:]]*//' ` — Remove leading whitespace from each line. ```bash sed 's/^[[:space:]]*//' messy.txt ``` `sed 's/&/\&/g; s//\>/g' ` — Escape HTML special characters. ```bash sed 's/&/\&/g; s//\>/g' input.html ``` ## Address Selection (Line Targeting) `sed 's///' ` — Substitute only on a specific line number. ```bash sed '3s/old/new/' config.txt ``` `sed ',s///g' ` — Substitute on a range of lines (from line n to line m). ```bash sed '10,20s/foo/bar/g' data.txt ``` `sed '$s///' ` — Substitute only on the last line. $ addresses the last line. ```bash sed '$s/$/;/' data.csv ``` `sed '//s///g' ` — Substitute only on lines matching a regex pattern. ```bash sed '/^#/s/TODO/DONE/g' script.sh ``` `sed '//,//s///g' ` — Substitute within a range defined by two regex patterns. ```bash sed '//,/<\/body>/s/class="old"/class="new"/g' page.html ``` `sed '1,//s///g' ` — Substitute from the first line until a pattern is matched. ```bash sed '1,/---/s/draft/published/g' post.md ``` `sed '0~2s///g' ` — Substitute on every 2nd line (GNU sed step address: start~step). ```bash sed '0~2s/^/>> /' data.txt ``` ## Deleting Lines `sed 'd' ` — Delete a specific line by number. ```bash sed '5d' data.txt ``` `sed ',d' ` — Delete a range of lines. ```bash sed '3,7d' data.txt ``` `sed '$d' ` — Delete the last line of the file. ```bash sed '$d' data.txt ``` `sed '//d' ` — Delete all lines matching a pattern. ```bash sed '/^#/d' config.ini ``` `sed '/^$/d' ` — Delete all empty lines. ```bash sed '/^$/d' messy.txt ``` `sed '/^[[:space:]]*$/d' ` — Delete all blank lines (empty or whitespace-only). ```bash sed '/^[[:space:]]*$/d' messy.txt ``` `sed '//,//d' ` — Delete all lines between two patterns (inclusive). ```bash sed '/BEGIN_GENERATED/,/END_GENERATED/d' output.txt ``` `sed '//!d' ` — Delete all lines NOT matching a pattern (inverse, like grep). ```bash sed '/ERROR/!d' log.txt ``` ## Inserting & Appending `sed 'i\' ` — Insert text before a specific line. ```bash sed '1i\# Configuration File' config.ini ``` `sed 'a\' ` — Append text after a specific line. ```bash sed '5a\# New section starts here' config.ini ``` `sed '//i\' ` — Insert text before lines matching a pattern. ```bash sed '/\[database\]/i\# Database settings' config.ini ``` `sed '//a\' ` — Append text after lines matching a pattern. ```bash sed '/^server {/a\ listen 443 ssl;' nginx.conf ``` `sed 'c\' ` — Replace (change) an entire line with new text. ```bash sed '3c\new_value = true' config.ini ``` `sed '//c\' ` — Replace entire lines matching a pattern with new text. ```bash sed '/^debug=/c\debug=false' config.ini ``` ## Back-References & Groups `sed 's//\1/g' ` — Capture a group with  and reference it with \1 in the replacement. ```bash sed 's/$version$=.*/\1=2.0/' config.ini ``` `sed -E 's/()/\1/g' ` — Extended regex mode. Use ( ) for groups instead of . ```bash sed -E 's/(version)=.*/\1=2.0/' config.ini ``` `sed -E 's/()()/\2\1/g' ` — Swap two captured groups using back-references. ```bash sed -E 's/([a-z]+), ([a-z]+)/\2 \1/g' names.txt ``` `sed 's/.*/(&)/' ` — The & in replacement refers to the entire matched text. ```bash sed 's/.*/(&)/' list.txt ``` `sed -E 's/([0-9]{4})-([0-9]{2})-([0-9]{2})/\3.\2.\1/g' ` — Reformat dates from YYYY-MM-DD to DD.MM.YYYY using three groups. ```bash sed -E 's/([0-9]{4})-([0-9]{2})-([0-9]{2})/\3.\2.\1/g' dates.txt ``` ## Printing & Output Control `sed -n 'p' ` — Print only a specific line. -n suppresses default output. ```bash sed -n '10p' data.txt ``` `sed -n ',p' ` — Print a range of lines. ```bash sed -n '5,15p' data.txt ``` `sed -n '//p' ` — Print only lines matching a pattern (like grep). ```bash sed -n '/ERROR/p' log.txt ``` `sed -n '//,//p' ` — Print lines between two patterns (inclusive). ```bash sed -n '/BEGIN/,/END/p' config.txt ``` `sed -n '$=' ` — Print the total number of lines in the file (like wc -l). ```bash sed -n '$=' data.txt ``` `sed '//q' ` — Quit after printing the first line matching a pattern. ```bash sed '/^END$/q' stream.txt ``` ## Multiple Commands `sed -e 's///g' -e 's///g' ` — Apply multiple substitution commands with -e flags. ```bash sed -e 's/foo/bar/g' -e 's/baz/qux/g' input.txt ``` `sed 's///g; s///g' ` — Chain multiple commands with semicolons. ```bash sed 's/http/https/g; s/www\.//g' urls.txt ``` `sed -f ` — Read sed commands from a script file (one command per line). ```bash sed -f transforms.sed input.txt ``` `sed '{ s///g; s///g; }' ` — Group multiple commands with curly braces. ```bash sed '/^title/{ s/old/new/g; s/draft/final/g; }' document.md ``` ## Transliteration `sed 'y///' ` — Transliterate characters (like tr). Maps each character one-to-one. ```bash sed 'y/abc/ABC/' input.txt ``` `sed 'y/ABCDEFGHIJKLMNOPQRSTUVWXYZ/abcdefghijklmnopqrstuvwxyz/' ` — Convert all uppercase letters to lowercase. ```bash sed 'y/ABCDEFGHIJKLMNOPQRSTUVWXYZ/abcdefghijklmnopqrstuvwxyz/' input.txt ``` ## Common Recipes `sed -E 's/^[[:space:]]+|[[:space:]]+$//g' ` — Trim leading and trailing whitespace from each line. ```bash sed -E 's/^[[:space:]]+|[[:space:]]+$//g' messy.txt ``` `sed '/^$/N;/^\n$/d' ` — Squeeze multiple consecutive blank lines into one. ```bash sed '/^$/N;/^\n$/d' messy.txt ``` `sed 's/^/ /' ` — Indent every line by 4 spaces. ```bash sed 's/^/ /' code.py ``` `sed '=' | sed 'N;s/\n/\t/'` — Add line numbers followed by a tab to each line. ```bash sed '=' script.sh | sed 'N;s/\n/\t/' ``` `sed -E 's/([^ ]+)/"\1"/g' ` — Wrap each word in double quotes. ```bash sed -E 's/([^ ]+)/"\1"/g' words.txt ``` `sed -E 's/,.*//' ` — Extract the first field from a CSV (everything before the first comma). ```bash sed -E 's/,.*//' data.csv ``` `sed -e :a -e '/\\$/N; s/\\\n//; ta' ` — Join lines ending with a backslash (line continuation). ```bash sed -e :a -e '/\\$/N; s/\\\n//; ta' Makefile ``` ## Pipelines ` | sed 's///g'` — Use sed as a filter in a pipeline to transform output. ```bash cat /etc/passwd | sed 's/:.*//' ``` ` | sed -n '//p'` — Filter output to show only matching lines. ```bash env | sed -n '/^PATH/p' ``` ` | sed '1d'` — Remove the first line (header) from command output. ```bash docker ps | sed '1d' ``` ` | sed 's/\x1b\[[0-9;]*m//g'` — Strip ANSI color codes from command output. ```bash ls --color=always | sed 's/\x1b\[[0-9;]*m//g' ``` ## Conclusion sed turns repetitive text edits into one-liners you can drop into scripts and pipelines. For everyday work, `s///g`, line deletion with `d` and selective printing with `-n …p` cover most cases. The one flag to treat with respect is `-i`: it overwrites the original file with no undo, so get into the habit of writing `-i.bak` to keep a backup – or run the command without `-i` first and eyeball the output. Be aware of GNU/BSD differences: GNU sed takes `-i` with no argument, whereas BSD/macOS sed requires `sed -i ''`; step addresses like `0~2` and `\x1b` escapes are GNU extensions too. ## Further Reading - [GNU sed manual](https://www.gnu.org/software/sed/manual/sed.html) – complete reference with all commands and addressing modes - [grymoire sed tutorial](https://www.grymoire.com/Unix/Sed.html) – classic, example-driven introduction to sed ## Related Commands - [awk](https://www.jpkc.com/db/en/cheatsheets/files-text/awk/) – field-aware text processing for column data and reports - [grep](https://www.jpkc.com/db/en/cheatsheets/files-text/grep/) – find the lines first, then transform them with sed - [tr](https://www.jpkc.com/db/en/cheatsheets/files-text/tr/) – fast character-level translation and deletion