Cheatsheet & Examples: sed
The sed command is a stream editor used to perform basic text transformations on an input stream (like a file or input from a pipeline). It can search, replace, delete, insert, and manipulate text based on patterns or line numbers.
Replace a specific pattern in a file
Example Usage:
sed 's/pattern/replacement/' file.txt
What it does:
Replaces the first occurrence of pattern with replacement on each line of the input file.
Command-line Arguments Explained:
s: The substitute command, which replaces text.pattern: The text or regular expression to search for.replacement: The text to replace the matched pattern.
Delete lines matching a pattern
Example Usage:
sed '/pattern/d' file.txt
What it does:
Deletes all lines that match the specified pattern.
Command-line Arguments Explained:
/pattern/: The text or regular expression to search for.d: The delete command.
Insert text before a matching line
Example Usage:
sed '/pattern/i\New line' file.txt
What it does:
Inserts a new line New line immediately before every line that matches pattern.
Command-line Arguments Explained:
/pattern/: The text or regular expression to search for.i\: The insert command, followed by the text to add.
Append text after a matching line
Example Usage:
sed '/pattern/a\New line' file.txt
What it does:
Appends a new line New line immediately after every line that matches pattern.
Command-line Arguments Explained:
/pattern/: The text or regular expression to search for.a\: The append command, followed by the text to add.
Substitute all occurrences in a line
Example Usage:
sed 's/pattern/replacement/g' file.txt
What it does:
Replaces all occurrences of pattern with replacement on each line of the input file.
Command-line Arguments Explained:
s: The substitute command.g: The global flag, which ensures all matches in the line are replaced.
Print specific lines
Example Usage:
sed -n '3p' file.txt
What it does: Prints only the third line of the input file (suppresses default output).
Command-line Arguments Explained:
-n: Disables default output (quiet mode).3p: The address3and the print commandp.
In-place editing of a file
Example Usage:
sed -i 's/foo/bar/' file.txt
What it does:
Modifies the file file.txt in-place, replacing foo with bar on each line.
Command-line Arguments Explained:
-i: Edits the file directly (in-place).s/foo/bar/: The substitute command.
Delete blank lines
Example Usage:
sed '/^$/d' file.txt
What it does: Removes empty lines from the input file.
Command-line Arguments Explained:
/^$/: Regular expression matching empty lines.d: Delete command.
Apply multiple commands
Example Usage:
sed -e 's/foo/bar/' -e 's/one/two/' file.txt
What it does: Applies multiple substitution commands to the input file.
Command-line Arguments Explained:
-e: Specifies an additional script to apply.s/foo/bar/: First substitution command.s/one/two/: Second substitution command.
Print lines containing a specific pattern
Example Usage:
sed -n '/error/p' file.txt
What it does:
Prints only the lines that contain the word error.
Command-line Arguments Explained:
-n: Suppresses default output./error/: The pattern to match.p: Print command.
Delete all lines except those matching a pattern
Example Usage:
sed '/pattern/!d' file.txt
What it does:
Deletes all lines that do not match the specified pattern.
Command-line Arguments Explained:
/pattern/: The address for lines to keep.!: Inverts the address match.d: Delete command.
Quit after a specific line
Example Usage:
sed '/pattern/q' file.txt
What it does:
Exits immediately after the first line matching pattern is found.
Command-line Arguments Explained:
/pattern/: The text or regular expression to search for.q: Quit command.
Substitute using backreferences
Example Usage:
sed 's/\(hello\) world/\1/' file.txt
What it does:
Replaces hello world with hello, using a backreference to capture groups.
Command-line Arguments Explained:
s: Substitute command.\(hello\)and\1: Capture group and backreference in the pattern.world: The text to replace.
Escape special characters in replacement
Example Usage:
sed 's/\/pattern/\/replacement/' file.txt
What it does:
Replaces /pattern with /replacement in the input file, properly escaping the slashes.
Command-line Arguments Explained:
s: Substitute command.\/patternand\/replacement: Escaped slashes in the pattern and replacement.
Substitute with case-insensitive matching
Example Usage:
sed 's/pattern/replacement/i' file.txt
What it does:
Replaces pattern with replacement, ignoring case in the match.
Command-line Arguments Explained:
s: Substitute command.i: Case-insensitive flag for the substitution.
Print line numbers with content
Example Usage:
sed '=' file.txt
What it does: Prints line numbers before each line of the input file.
Command-line Arguments Explained:
=: Print the line number of each line.
Replace text in a range of lines
Example Usage:
sed '3,5s/foo/bar/' file.txt
What it does:
Replaces foo with bar in lines 3 to 5 of the input file.
Command-line Arguments Explained:
3,5: The range of lines to apply the command to.s/foo/bar/: The substitute command.
Use a script file
Example Usage:
sed -f script.sed file.txt
What it does:
Reads and executes commands from the script file script.sed.
Command-line Arguments Explained:
-f: Specifies the script file to use.script.sed: The file containingsedcommands.file.txt: The input file to process.
Substitute using a new line character
Example Usage:
sed 's/pattern/replacement\n/' file.txt
What it does:
Replaces pattern with replacement followed by a newline.
Command-line Arguments Explained:
s: Substitute command.replacement\n: Includes a newline in the replacement text.
