Sed Cheat Sheet

wild characters
char	a single character, if not special, is matched against text
.	matches any character
*	matches a sequence of 0 or more repetitions of previous character/grouped regexp/class
.*	match all characters on every line (including empty ones)
\+	as *, but matches 1 or more
.\+	match all characters on every non-empty line
\?	as *, but only matches 0 or 1 character
special characters
\n	new line
\t	tab
\s	whitespace
\S	any non-whitespace character
\w	any word character (letter, digit, underscore)
\W	any non-word character
line beginning
^	matches the null string at the beginning of the line. What appears after ^ must appear at the beginning of the line
^#	match every line beginning with a # character
line ending
$	same as ^, but refers to the end of line
\$	dollar sign is escaped, so this matches lines ending with a single dollar
\\$	backslash is escaped, so this matches lines ending with a single backslash
number of sequences
\{i\}	as *, but matches exactly i number of sequences
\{i,\}	matches more than or equal to i sequences
\{i,j\}	matches between i and j sequences, inclusive
.\{9\}A$	matches an A that is the last character on line, with at least 9 preceding characters
^.\{15\}A	matches an A that is the 16th character on a line
groups and lists
[list]	matches any single character in list. Dashes indicate inclusive sequences.
[a-zA-Z0-9]	matches any letters or digits

sed '' file	auto print file contents to command line (essentially `cat` )
sed -n 'p' file	`-n` surpresses auto printing of each line; `p` prints each line (same result as above)
sed -n '1p' file	print only 1st line
sed -n '1,5p' file	print 1st through 5th lines
sed -n '1,+4p' file	print 1st line and next 4 lines (same output as above)
sed -n '1~2p' file	print every 2nd line beginning with the 1st
sed -n '/keyword/p' file	prints every line that contains keyword

sed '1~2d' file	delete every 2nd line beginning with the 1st (without `-n` option will also print what remains)
sed '/^$/d' file	matches any blank lines and passes them to the delete command
sed '/^$/!d' file	delete any line that is not blank (! inverts the address)
sed 's/[0-9]//g' file	delete all digits in all lines

sed '1~2d' file > newfile	delete every 2nd line from file, print remaining lines to newfile
sed -i '1~2d' file	delete every 2nd line "in-place", changes original file
sed -i.bak '1~2d' file	create backup file with .bak extension, edit the regular file in place

Note that source file is not affected by the basic commands; the edits are directed only to the command line unless explicitly directed to a file.

basic substitution
sed 's/oldword/newword/'	change 1st instance of oldword in each line to newword
sed 's\|dir1/oldword\|dir2/newword\|'	if string includes forward slash, other valid delimiters include pipe, underscore
start options
sed 'keyword/s/oldword/newword/' file	replace first instance of oldword with newword in any line that includes keyword
sed '1,3s/./newword/' file*	substitute everything in 1st, 2nd, and 3rd lines with newword
end flags
sed 's/oldword/newword/flag' file	flag can be any of the below
g	substitute every instance of oldword instead of just the first on each line (default behavior)
2	substitute only numberth instance of oldword on each line
p	print new pattern space for all lines where substitution was made
i	ignore case
other commands
sed 's/word/(&)/' file	`&` holds matched pattern (word) and puts parentheses around it
sed 's/old/new/';s/first/second/' file	semicolon strings together distinct commands
examples
sed -n 's/oldword/newword/2p' file	prints the lines where substitution took place

sed 's/.*/\"&\"/g'	add double quotes to line
sed "s\|.\|$dirname\|" file*	use double quotes to expand variables within replacement. Use a different delimiter if variable contains slashes (e.g. directory path)
var=$(sed -n "${i}p" file)	set variable equal to line in file, where line number i is also a variable

Also remember

sed

reads and operates line by line. Some commands modify the output stream directly (so can't use results for more editing unless pipe it to another

sed

command).

Sed Cheat Sheet (DRAFT) by [deleted]