sed.md

How to replace strings in a file

> echo '🍎\n🍊\n🍎' > foo.txt && cat foo.txt
🍎
🍊
🍎

> sed 's/🍎/🍋/' foo.txt
🍋
🍊
🍋

# in-place
# NB: BSD sed requires '' after -i, while GNU sed does not.
> sed -i '' 's/🍎/🍋/' foo.txt && cat foo.txt
🍋
🍊
🍋

How to delete blank lines, including whitespace-only lines, in a file

> echo '🍎\n\n  \n🍎' > foo.txt && cat foo.txt
🍎
(blank line)
  (two spaces)
🍎

> sed -e '/^[[:blank:]]*$/d' foo.txt
🍎
🍎

# in-place
> sed -i -e '/^[[:blank:]]*$/d' foo.txt && cat foo.txt
🍎
🍎

How to delete blank lines, excluding whitespace-only lines, in a file

> echo '🍎\n\n  \n🍎' > foo.txt && cat foo.txt
🍎
(blank line)
  (two spaces)
🍎

> sed -e '/^$/d' foo.txt
🍎
  (two spaces)
🍎

# in-place
# NB: BSD sed requires '' after -i, while GNU sed does not.
> sed -i -e '/^$/d' foo.txt && cat foo.txt
🍎
  (two spaces)
🍎

How to delete strings in a file

> echo '🍎\n🍊\n🍎' > foo.txt && cat foo.txt
🍎
🍊
🍎

> sed 's/🍎//g' foo.txt
(blank line)
🍊
(blank line)

# in-place
# NB: BSD sed requires '' after -i, while GNU sed does not.
> sed -i '' 's/🍎//g' foo.txt && cat foo.txt
(blank line)
🍊
(blank line)

How to prefix lines in a file

> echo '🍎\n🍊' > foo.txt && cat foo.txt
🍎
🍊

> sed 's/^/🍋/' foo.txt
🍋🍎
🍋🍊

# in-place
# NB: BSD sed requires '' after -i, while GNU sed does not.
sed -i '' 's/^/🍋/' foo.txt && cat foo.txt

How to suffix lines in a file

> echo '🍎\n🍊' > foo.txt && cat foo.txt
🍎
🍊

> sed 's/$/🍋/' foo.txt
🍎🍋
🍊🍋

# in-place
# NB: BSD sed requires '' after -i, while GNU sed does not.
> sed -i '' 's/$/🍋/' foo.txt && cat foo.txt
🍎🍋
🍊🍋

References

• GNU sed
  • https://www.gnu.org/software/sed/
• BSD sed
  • https://man.freebsd.org/cgi/man.cgi?sed(1)