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sed (stream editor) is a powerful text processing tool for filtering and transforming text. Edit files non-interactively, perform find-and-replace operations, and manipulate text streams efficiently.

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Basic Usage

• sed 's/old/new/' file - Substitute first occurrence per line

• sed 's/old/new/g' file - Substitute all occurrences

• sed 's/old/new/2' file - Substitute 2nd occurrence

• sed -i 's/old/new/g' file - Edit file in-place

• sed -i.bak 's/old/new/g' file - In-place with backup

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Substitution

• sed 's/pattern/replacement/' - Basic substitution

• sed 's/pattern/replacement/g' - Global substitution

• sed 's/pattern/replacement/i' - Case-insensitive

• sed 's/pattern/replacement/gi' - Global, case-insensitive

• sed 's|old|new|g' - Use different delimiter

• sed 's/old/new/; s/old2/new2/' - Multiple substitutions

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Line Selection

• sed -n '5p' file - Print line 5

• sed -n '5,10p' file - Print lines 5-10

• sed -n '5,$p' file - Print from line 5 to end

• sed -n '/pattern/p' file - Print matching lines

• sed -n '/start/,/end/p' file - Print range between patterns

• sed '5d' file - Delete line 5

• sed '/pattern/d' file - Delete matching lines

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Insertion & Appending

• sed '5i\new line' file - Insert before line 5

• sed '5a\new line' file - Append after line 5

• sed '/pattern/i\new line' file - Insert before match

• sed '/pattern/a\new line' file - Append after match

• sed '$a\new line' file - Append to end

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Advanced Patterns

• sed 's/^old/new/' - Match start of line

• sed 's/old$/new/' - Match end of line

• sed 's/old.*/new/' - Match rest of line

• sed 's/\(.*\)old\(.*\)/\1new\2/' - Capture groups

• sed 's/old/new/; t; s/old2/new2/' - Conditional

• sed -n 's/old/new/p' - Print only modified lines

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Multiple Commands

• sed -e 's/old/new/' -e 's/old2/new2/' file - Multiple expressions

• sed 's/old/new/; s/old2/new2/' file - Semicolon separator

• sed -f script.sed file - Read from script file

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Common Examples

Replace Text

sed 's/old/new/g' file.txt

Replace all occurrences.

In-Place Edit

sed -i 's/old/new/g' file.txt

Edit file directly.

Delete Lines

sed '/pattern/d' file.txt

Remove matching lines.

Print Range

sed -n '10,20p' file.txt

Print lines 10-20.

Add Line

sed '5a\new content' file.txt

Insert after line 5.

Remove Empty Lines

sed '/^$/d' file.txt

Delete blank lines.

Remove Leading Spaces

sed 's/^[ \t]*//' file.txt

Strip whitespace from start.

Remove Trailing Spaces

sed 's/[ \t]*$//' file.txt

Strip whitespace from end.

Number Lines

sed = file.txt | sed 'N;s/\n/\t/'

Add line numbers.

Extract Field

sed 's/.*:\(.*\):.*/\1/' file.txt

Extract between colons.

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Tips

• Use -i for in-place editing (be careful!)

• Use -i.bak to create backup

• Use -n with p to print only selected lines

• Use g flag for global substitution

• Use different delimiters (|, #) for complex patterns

• Combine with other tools in pipelines

• Test without -i first to verify changes

• Essential for batch text processing