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sed

By · Reviewed & last updated · Part of Linux & Bash Tutorial

sed (stream editor) transforms text line by line. Reach for it for in-place file edits, simple substitutions, and tiny ETL between commands. For multi-line transforms or more than a substitution, reach for awk or a script.

Real sed patterns

EXAMPLE
# 1) Basic substitute (PRINT to stdout — file untouched)
sed 's/foo/bar/' file.txt
sed 's/foo/bar/g' file.txt         # global on each line
sed 's/foo/bar/gI' file.txt        # case-insensitive

# 2) In-place edit
sed -i 's/foo/bar/g' file.txt      # Linux — overwrites
sed -i.bak 's/foo/bar/g' file.txt  # save backup
sed -i '' 's/foo/bar/g' file.txt   # macOS — requires '' argument

# 3) Use a different delimiter when the pattern has slashes
sed 's|/usr/local|/opt|g' paths.txt

# 4) Address — apply only to certain lines
sed '2,4 s/foo/bar/g'   file.txt   # lines 2-4 only
sed '/^#/d'             file.txt   # delete lines starting with #
sed '/ERROR/,/END/d'    file.txt   # delete from ERROR through END
sed -n '10,20p'         file.txt   # print only lines 10-20

# 5) Capture groups + backrefs (ERE flag -E)
sed -E 's/^([A-Z]+): (.*)/[\1] \2/' log.txt
#   INFO: ready  →  [INFO] ready

# 6) Multiple commands
sed -e 's/foo/bar/g' -e '/wip/d' file.txt
sed -f script.sed file.txt           # commands from a file

# 7) Insert / append / change whole lines
sed '3 i\
NEW LINE' file.txt                  # insert before line 3
sed '5 a\
APPENDED' file.txt                  # append after line 5
sed '7 c\
REPLACED' file.txt                  # replace line 7

# 8) Common one-liners
sed -n '$=' file.txt                # count lines (= wc -l)
sed '/^$/d' file.txt                # remove blank lines
sed 's/[[:space:]]*$//' file.txt    # strip trailing whitespace
sed -E 's/<[^>]+>//g' page.html     # naive HTML strip
sed 'y/abc/ABC/' file.txt           # transliterate (like tr)

# 9) Pipe-friendly transforms
cat config.json | sed -E 's/"version": "[^"]+"/"version": "1.4.0"/' > new.json
echo 'hello world' | sed 's/world/Ada/'

Why it matters

For one-line substitutions, sed is unbeatable. For anything multi-line, reach for awk or python — sed’s line-oriented model makes hold-space / branch-label scripts painful to read.

Tip: Tweak the snippet with Try it Yourself », then sit the quiz at the bottom of the page.

Example

Example
sed -i 's/foo/bar/g' file.txt
sed -n '5,10p' file
Try it Yourself »

Discussion

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