Mastering sed: Essential Commands and Advanced Techniques for Text Processing

Basic sed commands

Basic syntax

sed OPTIONS… [SCRIPT] [INPUTFILE…]

Common options:

-n, --quiet: suppress automatic printing of the pattern space

-i: edit files in place (default does not modify the original file)

-e: allow multiple commands (scripts) to be applied

-f /path/from/sed_script: read the processing script from a file

-r: use extended regular expressions

sed command options

Replacement flags g: global replacement within the line w: write the line to a file x: exchange the contents of the pattern space and the hold space y: transliterate characters (not a regular‑expression operation)

Single‑line commands

a: append text after the current line (the text follows the a command)

c: replace the selected lines with new text (the text follows the c command)

d: delete the selected line(s)

i: insert text before the current line (the text follows the i command)

p: print the selected lines, usually used together with the -n option

s: substitute a pattern, e.g., 1,20s/old/new/g n: read the next input line and continue processing

y: transliterate characters, e.g.,

y/abc/ABC/

# vim xbz
cat xbz
a b c
d
c
b
a
# sed '3abbxxxx' xbz   # add after line 3 (line 4)
# sed '/c/abbxxxx' xbz # add after lines matching c

# cat xbz
a b c
d
c
b
a
# sed '2cxxb' xbz      # replace line 2
# sed '/d/caa' xbz     # replace line matching d

# cat xbz
a b c
d
c
b
a
# sed '1d' xbz         # delete first line
# sed '/c/d' xbz        # delete lines matching c

# cat xbz
a b c
d
c
b
a
# sed '2i3838' xbz    # insert after line 2
# sed '/c/i6868' xbz   # insert before lines matching c

# cat xbz
a b c
d
c
b
a
# sed -n '/b/p' xbz   # print only lines containing b

# cat xbz
a b c
d
c
bbb
a
# sed 's/b/a/' xbz    # replace first b on each line with a
# sed 's/b/a/g' xbz    # replace all b's on each line with a

# cat xbz
a b c
d
c
bbb
a
# sed -n '/a/n;p' xbz # print lines after a

# cat xbz
a b c
d
c
bbb
a
# sed '3y/c/C/' xbz   # transliterate c to C on line 3

Advanced sed commands

Pattern space and hold space

Pattern space is the buffer that holds the current line being processed. The hold space is a secondary buffer that retains its contents across cycles and is not printed automatically. Commands such as h, H, g, G, x allow interaction between the two spaces.

Multi‑line space commands

Multi‑line space commands N: read the next line and append it to the pattern space P: print up to the first newline in the pattern space D: delete up to the first newline and restart the cycle without reading a new line

# cat xbz.txt
Consult Section 3.1 in the Owner and Operator
Guide for a description of the tape drives
available on your system.
# sed -n '/Operator$/{N;p}' xbz.txt
Consult Section 3.1 in the Owner and Operator
Guide for a description of the tape drives
# sed -n '/Operator$/{N;s/Owner and Operator
Guide/installation Guide/g;p}' xbz.txt
Consult Section 3.1 in the installation Guide for a description of the tape drives

# cat test
This is the header line.
This is a data line.
This is the last line.
# sed '/^$/{N ; /header/D}' test
This is the header line.
This is a data line.
This is the last line.

# cat xxb
Here are examples of the UNIX
System. Where UNIX
System appears, it should be the UNIX
Operating System.
# sed -n '/UNIX$/p' xxb
Here are examples of the UNIX
System. Where UNIX
System appears, it should be the UNIX

Hold (h/H): copy or append the pattern space to the hold space

Get (g/G): copy or append the hold space back to the pattern space

Exchange (x): swap the contents of the hold and pattern spaces