sed.md

sed

• Intro

• Flags

• Useful commands

• Useful commands using sed.

Intro

• sed (stream editor)

Flags

• -i -- in place text editing
• s -- the substitute command
• g -- global (replace all occurrence)
• original -- original text
• new -- new text

Useful commands

Grep lines b/w two strings

sed -n '/test1/,/test2/p' file.txt

• In found lines search strings will be included.

• To exclude search strings

sed -n '/test1/,/test2/{/test1/b;/test2/b;p}' file.txt

Replace a line in a file

sed -i '/original/c\new' file.txt

Replace all occurrences of the string in a file

sed -i 's/original/new/g' file.txt

Replace all occurrences of the string using env variable

sed -i "s/$original/new/g" file.txt

• NOTE: " is used instead of '.
• NOTE: $original means env variable is used.

$original can be used with Bash parameter expansion trick which allows you to use default value if env variable is not set. For example

original="${ORIGINAL_ENV:-default_value}"

Let's assume ORIGINAL_ENV is not set, original variable will end up with having default_value.

Replace all occurrences of the string having / (forward-slash)

sed -i "s|$original|new|g" file.txt

Replace , with newline

echo "a,b" | sed 's/,/\n/g'

Replace / with newline

echo "a/b" | sed 's/\//\n/g'

Replace (space) with newline

echo "a b" | sed 's/\s/\n/g'

Replace one or more space(s) with newline

echo "a b" | sed 's/\s\+/\n/g'
echo "a    b" | sed 's/\s\+/\n/g'

Replace leading spaces or tabs

echo "    a b" | sed -e 's/^[ \t]*//'
echo "		a b" | sed -e 's/^[ \t]*//'

Replace trailing spaces

echo "a b  " | sed -e 's/[[:space:]]*$//'
echo "a b       " | sed -e 's/[[:space:]]*$//'

• :space -- Use posix standard to specify space which will handle tabs too.

Remove lines starting with string

sed -i '/^string/d' file.txt