SED

Stream Editor#

A Stream Text Processor, authored by Lee E. McMahon.

Basic Syntax#

sed [OPTIONS] 'command' file

• OPTIONS: Command options.
• command: Print, replace, delete, etc.
• file: The file to process; if omitted, reads from STDIN.

Omitting file enters interactive mode, executing one line at a time.

Execution Process#

• Reading a line of data:
  • With a match rule:
    • Match successful: Executes related operations.
    • Match failed: Prints data as is.
  • Without a match rule: Executes related operations.

Command Quotes#

• Single quotes: Reduces the impact of escape characters, preferably used.
• Double quotes: Can use variable parameters, requires handling special characters.

Common Examples#

Replace First Occurrence#

Replace the first occurrence of ‘a’ with ‘b’.

echo 'aba' | sed 's/a/b/'

bba

Replace Nth Occurrence#

Replace the Nth occurrence of ‘a’ with ‘b’.

echo 'aba' | sed 's/a/b/2'

abb

Replace All Occurrences#

echo 'aba' | sed 's/a/b/g'

bbb

Execute Mult Commands#

Can use ; to separate, or use the -e option.

echo 'aba' | sed 's/a/b/; s/a/c/'

echo 'aba' | sed -e 's/a/b/' -e 's/a/c/'

bbc

Using Command File#

The cmd.sed file content is as follows.

s/a/b/
s/a/c/

echo 'aba' | sed -f cmd.sed

bbc

Print Only Replaced Lines#

-n indicates suppressing output, p indicates only outputting matched lines.

echo '
aa bb
cc dd
' | sed -n 's/aa/bb/p'

bb bb

Write Result to File#

echo '
aa bb
cc dd
' | sed 's/aa/bb/w out.txt'

cat out.txt

bb bb

Modify Delimiter#

Can use another symbol to replace the command delimiter /.

echo '/bin/sh' | sed 's#/sh#/bash#'

/bin/bash

Specify Line Match#

Match the 2nd line.

sed '2s/aa/bb/'

Match lines 2-4.

sed '2,4s/aa/bb/'

Match lines 2 to the last.

sed '2,$s/aa/bb/'

Specify Command Group#

sed '2{s/cc/aa/; s/dd/bb/}'

sed '2,4{
s/cc/aa/
s/dd/bb/
}'

Delete All Lines#

sed 'd'

Delete Specific Lines#

sed '1d'

sed '2,4d'

sed '2,$d'

Delete Matched Lines#

sed '/aa bb/d'

Insert a Line Before#

echo "hello" | sed 'i\New Line'

Insert a Line After#

echo "hello" | sed 'a\New Line'

Specify Line Insert#

sed '3i\New Line'

Matched Line Insert#

sed '/cc/i\New Line'

Insert Multiple Lines#

Must use \.

sed '2i\
New Line 1\
New Line 2
'

Modify Line#

sed '2c\
Change Line 1\
Change Line 2
'

sed '/aa/c\
Change Line 1
'

Single Char Replace#

echo 'aabbcc' | sed 'y/ac/ca/'

ccbbaa

Print Specific Lines#

sed -n '2,5p'

Print Before/After Replacement#

sed -n '/aa/{p; s/aa/cc/p}'

Print Line Number#

sed -n '/bb/{=; p}'

Reading from File#

Create foo and bar files.

echo -e 'aa\nbb' > foo
echo -e '11\n22' > bar

Read from the foo file and insert after the first line of bar.

sed '1r foo' bar

11
aa
bb
22

Match string then insert.

sed '/22/r foo' bar

11
22
aa
bb

Match string, insert, and use d to delete the matched line.

sed '/22/{
r foo
d
}' bar

11
aa
bb

The following will report a syntax error.

# Will error
sed '/22/{r foo; d}' bar

It’s not impossible to do it in one line.

sed '/22/r foo' bar | sed '/22/d'