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Franz Wong
Franz Wong

Posted on • Updated on

sed cookbook

#sed #tutorial #cookbook

Table of contents

Write the result to another file

Content of file_1 (before command is executed)

Hello World
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Command

sed 's/Hello/Goodbye/;w file_2' file_1
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Content of file_1 (after command is executed)

Hello World
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Content of file_2 (after command is executed)

Goodbye World
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Replace first occurrence on every

Input file

aa
bb bb
aa
bb
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Command

sed 's/bb/dd/' file
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Output

aa
dd bb
aa
dd
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Replace values of all occurrences

Input file

aa
bb bb
aa
bb
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Command

sed 's/bb/dd/g' file
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Output

aa
dd dd
cc
dd
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Replace value of first occurrence in the file

Input file

aa
bb bb
aa
bb
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Command

It only works on GNU sed.
See also: https://www.gnu.org/software/sed/manual/html_node/Range-Addresses.html

sed '0,/bb/{s/bb/dd/}' file
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Output

aa
dd bb
cc
bb
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Replace all occurrences on n-th line

Input file

aa
bb bb
aa
bb
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Command

# replace all occurrences on 2nd line
sed '2s/bb/dd/g' file
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Output

aa
dd dd
aa
bb
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Replace all occurrences within a range of lines

Input file

aa1
aa2
aa3
aa4
aa5
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Command

# replace occurrences from 2nd line to 4th line
sed '2,4s/aa/dd/g' file
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Output

aa1
dd2
dd3
dd4
aa5
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Replace all occurrences on every line matching pattern

Input file

a 1
a 2
a 1 x
b 1
b 2
b 1 x
c 1
c 2
c 1 x
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Command

# replace "1" with "10" on all the lines containing "b"
sed '/b/s/1/10/g' file1
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Output

a 1
a 2
a 1 x
b 10
b 2
b 10 x
c 1
c 2
c 1 x
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Replace all occurrences on every line NOT matching pattern

Input file

a 1
a 2
a 1 x
b 1
b 2
b 1 x
c 1
c 2
c 1 x
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Command

# replace "1" with "10" on all the lines NOT containing "b"
sed '/b/!s/1/10/g' file
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Output

a 10
a 2
a 10 x
b 1
b 2
b 1 x
c 10
c 2
c 10 x
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Replace first occurrence after a pattern

Input file

server-alpha:
    host: '192.168.0.1'
    port: 9090

server-beta:
    host: '192.168.0.1'
    port: 9091

server-charlie:
    host: '192.168.0.1'
    port: 9092
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Problem

Change the host of server-beta to 192.168.0.2. Values of other hosts remain unchanged.

Command

sed -e '/server-beta/! b' \
    -e ':label1' \
    -e 's/192.168.0.1/192.168.0.2/' \
    -e 't label2' \
    -e 'n' \
    -e 'b label1' \
    -e ':label2' \
    -e 'n' \
    -e 'b label2' \
    file
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Output

server-alpha:
    host: '192.168.0.1'
    port: 9090

server-beta:
    host: '192.168.0.2'
    port: 9091

server-charlie:
    host: '192.168.0.1'
    port: 9092
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Explanation

It uses the sed branching commands b and t.

  • /server-beta/! b - if pattern space doesn't contain server-beta, it will jump to the end of script.

  • :label1 - declare a label with name label1

  • s/192.168.0.1/192.168.0.2/ - Replace 192.168.0.1 with 192.168.0.2

  • t label2 - if the previous replacement is done, jump to label2.

  • n - read next line from input and put to pattern space or exit if no more line from input

  • b label1 - jump to label1

  • :label2 - declare a label with name label2

  • n - read next line from input and put to pattern space or exit if no more line from input

  • b label2 - jump to label2

Pseudo code

input = readLineFromInput()
while (input != null) {
    patternSpace.append(input)

    if (patternSpace.contains("server-beta")) {
        while (true) { // label1
            if (patternSpace.replace("192.168.0.1", "192.168.0.2")) {
                break // jump to label2
            }
            /** start of n **/
            display(patternSpace)
            patternSpace.clear()
            input = readLineFromInput()
            if (input == null) {
                exit
            }
            patternSpace.append(line)
            /** end of n **/
        }

        while (true) { // label2
            /** start of n **/
            display(patternSpace)
            patternSpace.clear()
            input = readLineFromInput()
            if (input == null) {
                exit
            }
            patternSpace.append(line)
            /** end of n **/
        }
    }

    display(patternSpace)
    patternSpace.clear()
    input = readLineFromInput()
}
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Delete lines matching pattern

Input file

aa1
bb2
cc3
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Command

sed /bb/d file
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Output

aa1
cc3
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Delete n-th line

Input file

aa1
aa2
aa3
aa4
aa5
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Command

# delete 2nd line
sed 2d
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Output

aa1
aa3
aa4
aa5
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Insert before line

Input file

aa1
bb2
cc3
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Command

sed "/bb/i bb_before" file
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Output

aa1
bb_before
bb2
cc3
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Insert after line

Input file

aa1
bb2
cc3
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Command

sed "/bb/a bb_after" file
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Output

aa1
bb2
bb_after
cc3
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Use other delimiter

Input file

/aa/bb/cc/dd
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Problem

It is too clumsy to escape slash.

sed 's/bb/bb1\/bb2\/bb3/' file
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Command

It is clearer if # is used.

sed 's#bb#bb1/bb2/bb3#' file
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Output

/aa/bb1/bb2/bb3/cc/dd
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Actually any character can be used.

These are all valid and produce same output.

# , is used
sed 's,bb,bb1/bb2/bb3,' file

# $ is used
sed 's$bb$bb1/bb2/bb3$' file

# a is used
sed 'sabbabb1/bb2/bb3a' file
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But you can't use character which is inside the pattern.

# b is used
sed 'sbbbbbb1/bb2/bb3b' file
# sed: -e expression #1, char 5: unknown option to `s'

# 1 is used
sed 's1bb1bb1/bb2/bb31' file
# sed: -e expression #1, char 9: unknown option to `s'
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