sed is a stream editor command available on Unix-compatible systems.
sed is quite a powerful tool, but the learning curve is also high comparing to other similar tools such as grep or awk.
Almost every time I want to do something with sed, I need to look it up and search for some examples.
So, I decided to compile a concise tutorial for sed that covers the most common use-cases.
With sed, you usually specify a few options and a script and feed it with an input file.
sed <options> <script> <input_file>
Options
Here are some options for sed command that you most likely need to know about them.
| Option | Description |
|---|---|
-i | Edits the input file in-place. |
-e | Specifies the scripts for editing. |
-n | Suppresses printing each line of input. |
Commands
Here are some common commands that you may use in sed scripts:
| Command | Description |
|---|---|
1 | Applies a command to only to the first occurrence. |
2 | Applies a command to only to the second occurrence. |
g | Global applies a command to every occurrence. |
i | Matches in a case-insensitive manner. |
p | Prints the matching patterns to standard output. |
d | Deletes the matching patterns from output or input file. |
s/regexp/replacement/ | Replaces a regexp instance with the replacement. |
Regular Expressions
| Pattern | Description |
|---|---|
| ^ | Matches the beginning of lines. |
| $ | Matches the end of lines. |
| . | Matches any single character. |
| * | Matches zero or more occurrences. |
| [] | Matches a class of characters. |
Examples
| Example | Description |
|---|---|
sed -n '2p' input.txt | Shows a single line by line number. |
sed -n '2!p' input.txt | Shows all lines except one line number. |
sed -n '2p;4p' input.txt | Shows multiple lines by line numbers. |
sed -n '2,4p' input.txt | Shows multiple lines by a range. |
sed -n '2,4!p' input.txt | Shows all lines except a range of lines. |
sed -n '2,$p' input.txt | Shows all lines after a line number. |
sed -n '2,$!p' input.txt | Shows all lines before a line number. |
sed -i '2d' input.txt | Deletes a particular line in-place. |
sed -i '2,4d' input.txt | Deletes a range of lines in-place. |
sed -i '/regex/d' input.txt | Deletes all lines matching regex in-place. |
sed -i '/regex/,$d' input.txt | Deletes all lines after a line matching regex in-place. |
sed -i 's/foo/bar/g' input.txt | Replaces all occurrences of foo with bar in-place. |