Mastering sed: Essential Commands, Options, and Real‑World Examples

Introduction to sed

sed is a stream editor that efficiently performs replacements, deletions, insertions, and other operations on text data line by line without modifying the original file.

It reads input data into a temporary buffer called the pattern space , matches it against given conditions, and executes specific sed commands when a match succeeds.

Command Syntax

sed [OPTION]... {script-only-if-no-other-script} [input-file]...

Examples:

cat filename | sed 's/pattern/replacement/'

Common Options

-n, --quiet, --silent

: suppress automatic printing of pattern space (often used with p). --debug: annotate program execution for debugging. -e script, --expression=script: add a script directly on the command line (multiple expressions allowed). -f script-file, --file=script-file: read commands from a script file. -i[SUFFIX], --in-place[=SUFFIX]: edit files in place, optionally creating a backup. -E, -r, --regexp-extended: use extended regular expressions. --posix: disable GNU extensions and follow POSIX syntax.

Delimiters

While / is the default delimiter, any character can be used. When a delimiter appears inside the expression, it must be escaped.

sed 's\|foo\|bar\|g' filename

Variable References

sed scripts are usually single‑quoted. If the script contains variable names, use double quotes.

foo="world"
echo "hello $foo" | sed "s/$foo/librarookie/"

Editing Commands

p

: print the current line (often with -n). l: print the line showing control characters. =: print the current line number. a\text: append text after the matched line. i\text: insert text before the matched line. c\text: replace the entire matched line with text . d: delete the matched line. r filename: read filename and insert its contents after the matched line. w filename: write the matched line to filename . s/regexp/replace/: substitute the first match on a line. s/regexp/replace/g: global substitution on a line. q: quit processing immediately.

Advanced Commands

h

: copy pattern space to hold space. H: append pattern space to hold space. g: copy hold space back to pattern space. G: append hold space to pattern space. x: exchange pattern space and hold space. n: read the next line into pattern space. N: read the next line and append it to pattern space. t label / b label: conditional or unconditional jumps to a label. y/source/dest/: transliterate characters.

Combining Multiple Expressions

Use -e to specify several expressions, separate them with semicolons, or pipe multiple sed commands.

sed -e 's/foo/bar/' -e '/baz/d' filename

Scripts (-f)

A sed script file contains a list of commands, one per line. Blank lines and comments (starting with #) are ignored.

# Replace "old_string" with "new_string" on the first line
1s/old_string/new_string/
# Delete lines containing "delete_this_line"
/delete_this_line/d

Pattern Space and Hold Space

The pattern space holds the current line being processed. The hold space is a secondary buffer that can store data for later use, enabling complex multi‑line operations.

# Copy lines containing "test" to hold space and append at end of file
sed -e '/test/h' -e '$G' file

Printing Odd or Even Lines

# Odd lines
sed -n 'p;n' file
# Even lines
sed -n 'n;p' file
# Using step syntax
sed -n '1~2p' file   # odd
sed -n '2~2p' file   # even

Quit After a Certain Line

# Stop after printing line 10
sed '10q' filename