GNU sed (stream editor) is a non-interactive command-line text editor

sed is commonly used to filter text or edit, i.e., it takes text input, performs some operation (or set of operations) on it, and outputs the modified text.

sed is typically used for extracting part of a file using pattern matching or substituting multiple occurrences of a string within a file.
— GNU sed

Examples

Replace all apple occurrences with mango and print the result to stdout (don’t do any file modifications):

echo "I have 1 apple and he has 2 apples." | sed 's/apple/mango/g'

Results: I have 1 mango and he has 2 mangos.

Replace all apple occurrences with mango in a specific file and overwrite the original file in place:

# -i[SUFFIX], --in-place[=SUFFIX]
#   edit files in place (makes backup if SUFFIX supplied).
# /g - global replacement flag
 
echo "I have 1 apple and he has 2 apples." > /tmp/sed_test
sed -i 's/apple/mango/g' /tmp/sed_test
cat /tmp/sed_test

Results: I have 1 mango and he has 2 mangos.

Replace all apple (extended regex) occurrences with APPLE (extended regex) in all input lines and print the result to stdout:

# -E, --regexp-extended
#   use extended regular expressions.
 
echo "I have 1 apple and he has 2 apples." | sed -E 's/(apple)/\U\1/g'

Results: I have 1 APPLE and he has 2 APPLEs.

Remove leading spaces:

printf "  One\n  Two\n  Three\n  Four\n  Five"|sed -E 's/^\s+//g'

Results:

One
Two
Three
Four
Five

Remove empty lines and print results to stdout:

printf "One\n\n\nTwo\nThree\nFour\nFive\nSix\nSeven\nEight\nNine\n"|sed '/^$/d'

Results:

One
Two
Three
Four
Five
Six
Seven
Eight
Nine

Special characters:

# It can become necessary to escape special characters in your string.
fd Wiki -a -d 1 | sed 's/\/home//'
 
# # Change your sed delimiter to a pipe to avoid escaping slashes.
fd Wiki -a -d 1 | sed 's|/home||'

Results:

/inom/Wiki/Wikipedia-Glossary_of_computer_science.md
/inom/Wiki/Wikipedia-Glossary_of_computer_science.md

Execute a specific script file (sed script) and print the result to stdout:

# -f script-file, --file=script-file
#   add the contents of script-file to the commands to be executed
cat >/tmp/script.sed <<EOL
s/public/shared/g
s/System/User/g
s/println/echo/g
EOL
 
cat >/tmp/data.txt <<EOL
public class Main {
  public static void main(String[] args) {
    System.out.println("Hello World");
  }
}
EOL
sed -i -f /tmp/script.sed /tmp/data.txt
cat /tmp/data.txt

Results:

shared class Main {
  shared static void main(String[] args) {
    User.out.echo("Hello World");
  }
}

Print just the first line to stdout:

# -n, --quiet, --silent
#   suppress automatic printing of pattern space
printf "I have 1 apple and he has 2 apples.\nAnd you?" | sed -n '1p'

Results: I have 1 apple and he has 2 apples.

Delete the first line of a file:

# -i[SUFFIX], --in-place[=SUFFIX] - edit files in place (makes backup if SUFFIX
# supplied).
# d - Delete pattern space.  Start next cycle.
 
printf "One\nTwo\nThree\nFour\nFive\nSix\nSeven\nEight\nNine\n" > /tmp/sed_test
sed -i 1d /tmp/sed_test
cat /tmp/sed_test

Results:

Two
Three
Four
Five
Six
Seven
Eight
Nine

Delete the 4th line in a file and print the result to stdout:

# d - Delete pattern space.  Start next cycle.
 
printf "One\nTwo\nThree\nFour\nFive\nSix\nSeven\nEight\nNine\n" > /tmp/sed_test
sed '4d' /tmp/sed_test

Results:

Two
Three
Four
Five
Six
Seven
Eight
Nine
/tmp/mdeval//GNUSedmd_152_181.sh: line 13: *Results:*: command not found
/tmp/mdeval//GNUSedmd_152_181.sh: line 12: Two: command not found
/tmp/mdeval//GNUSedmd_152_181.sh: line 13: Three: command not found
/tmp/mdeval//GNUSedmd_152_181.sh: line 14: Four: command not found
/tmp/mdeval//GNUSedmd_152_181.sh: line 15: Five: command not found
/tmp/mdeval//GNUSedmd_152_181.sh: line 16: Six: command not found
/tmp/mdeval//GNUSedmd_152_181.sh: line 17: Seven: command not found
/tmp/mdeval//GNUSedmd_152_181.sh: line 18: Eight: command not found
/tmp/mdeval//GNUSedmd_152_181.sh: line 19: Nine: command not found
/tmp/mdeval//GNUSedmd_152_181.sh: line 26: Delete: command not found
/tmp/mdeval//GNUSedmd_152_181.sh: line 24: stdoutsh: command not found
One
Two
Three
Five
Six
Seven
Eight
Nine

Insert a new line at the first line of a file:

# -i[SUFFIX], --in-place[=SUFFIX] - edit files in place (makes backup if SUFFIX
# supplied).
# i\text - Insert text, which has each embedded newline preceded by a backslash.
 
sed -i '1i\your new line text\' path/to/file

Results: sed: can't read path/to/file: No such file or directory

Replace every occurrence of ‘hello’ with ‘world’ on lines 10-20:

# s/regexp/replacement/ - Attempt to match regexp against the pattern space.  If
# successful, replace that portion matched with replacement.
 
printf "hello\nhello\nhello\nhello\nhello\nhello\nhello\nhello\nhello\n" >\
/tmp/sed_test
sed '1,2s/hello/world/' /tmp/sed_test

Results:

world
world
hello
hello
hello
hello
hello
hello
hello

# To replace newlines in multiple lines:
sed ':a;N;$!ba;s/\n//g' <file>

# To insert a line before a matching pattern:
sed '/Once upon a time/i\Chapter 1'

# To add a line after a matching pattern:
sed '/happily ever after/a\The end.'

Replace mulitline substrngs in multiple files:

for i in ./appmanifest_*.acf; do
    sed -i 's/"AutoUpdateBehavior"\t\t"0"/"AutoUpdateBehavior"\t\t"1"/g' $i;
done

Replace &#10;<br> with <br> in all *.md files in current directory:

find . -type f -name '*.md' -exec sed -i 's/&#10;<br>/<br>/g' {} \;

External links

• sed, a stream editor