📖 Guide

Sed — Complete Reference

Comprehensive sed cheat sheet covering substitution, address ranges, transforms, hold space, branching, and common one-liners.

54 commands across 8 categories

Basic Substitution Address Ranges Delete & Insert Transform Hold Space Branching Flags Common One-liners

Basic Substitution

Command	Description
`sed 's/old/new/' file`	Replace first occurrence of 'old' with 'new' on each line
`sed 's/old/new/g' file`	Replace all occurrences of 'old' with 'new' on each line
`sed -i 's/old/new/g' file`	Edit file in-place (modifies the original file)
`sed -i.bak 's/old/new/g' file`	Edit in-place with backup (.bak extension)
`sed 's\|/usr/bin\|/usr/local/bin\|g' file`	Use alternate delimiter (\| instead of /) for paths
`sed 's/old/new/2' file`	Replace only the 2nd occurrence on each line
`sed 's/old/new/gi' file`	Case-insensitive replacement (GNU sed)
`sed 's/.*://' file`	Delete everything up to and including the last colon

Address Ranges

Command	Description
`sed '3s/old/new/' file`	Replace only on line 3
`sed '2,5s/old/new/' file`	Replace on lines 2 through 5
`sed '/pattern/s/old/new/' file`	Replace only on lines matching pattern
`sed '1,/pattern/s/old/new/' file`	Replace from line 1 to first line matching pattern
`sed '/start/,/end/s/old/new/' file`	Replace between lines matching start and end patterns
`sed '$ s/old/new/' file`	Replace only on the last line
`sed '0~2s/old/new/' file`	Replace on every 2nd line (GNU sed: start~step)

Delete & Insert

Command	Description
`sed '3d' file`	Delete line 3
`sed '/pattern/d' file`	Delete all lines matching pattern
`sed '2,5d' file`	Delete lines 2 through 5
`sed '/^$/d' file`	Delete all blank lines
`sed '3i\inserted text' file`	Insert text before line 3
`sed '3a\appended text' file`	Append text after line 3
`sed '3c\replacement line' file`	Replace entire line 3 with new text
`sed '/pattern/r other.txt' file`	Read and insert contents of other.txt after matching lines

Transform

Command	Description
`sed 'y/abc/ABC/' file`	Transliterate characters (a→A, b→B, c→C)
`sed 's/.*/\U&/' file`	Convert entire line to uppercase (GNU sed)
`sed 's/.*/\L&/' file`	Convert entire line to lowercase (GNU sed)
`sed 's/\b./\u&/g' file`	Capitalize first letter of every word (GNU sed)
`sed 's/[[:space:]]*$//' file`	Remove trailing whitespace from each line
`sed 's/^[[:space:]]*//' file`	Remove leading whitespace from each line

Hold Space

Command	Description
`h`	Copy pattern space to hold space (overwrite)
`H`	Append pattern space to hold space
`g`	Copy hold space to pattern space (overwrite)
`G`	Append hold space to pattern space
`x`	Exchange pattern space and hold space
`sed -n '1!G;h;$p' file` e.g. Uses hold space to accumulate lines in reverse	Reverse line order of file (like tac)

Branching

Command	Description
`:label`	Define a label for branching
`b label`	Branch (jump) to label unconditionally
`t label`	Branch to label only if last s/// succeeded
`T label`	Branch to label only if last s/// did NOT succeed (GNU sed)
`sed ':a;N;$!ba;s/\n/ /g' file` e.g. Loops with :a label until last line, then substitutes	Join all lines into one (replace newlines with spaces)

Flags

Command	Description
`sed -n 'p' file`	-n suppresses auto-print; only explicit p prints
`sed -e 'cmd1' -e 'cmd2' file`	-e allows multiple commands
`sed -f script.sed file`	-f reads commands from a script file
`sed -E 's/(group)/\1/' file`	-E enables extended regex (ERE) for cleaner syntax
`sed -n 's/pattern/replace/p' file`	Print only lines where substitution was made
`sed -n 's/pattern/replace/w output.txt' file`	Write lines where substitution was made to output.txt

Common One-liners

Command	Description
`sed -n '5,10p' file`	Print lines 5 through 10
`sed -n '1p' file`	Print only the first line (like head -1)
`sed 'G' file`	Double-space a file (insert blank line after each line)
`sed '/^#/d' file`	Remove comment lines (starting with #)
`sed 's/<[^>]*>//g' file`	Strip HTML tags
`sed -n '/pattern/=' file`	Print line numbers of matching lines
`sed '=' file \| sed 'N;s/\n/\t/'`	Number all lines with a tab separator
`sed '$!N;/^\(.*\)\n\1$/!P;D' file`	Remove consecutive duplicate lines (like uniq)

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