sed

src: https://wizardzines.com/comics/sed/

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Text conversion and substitution

# match "pattern" against the pattern space and replace the 1st occurrence of each line
# with "replacement" if successful matched
sed 's/pattern/replacement/'
# you can refer the pattern matching sub-expressions with special escapes \1 through \9
# /!\ parenthesis and plus sign must be escaped, otherwise sed will consider it as a simple character
sed 's/^foo\(\w\+\)/\1/'
 
# replace only the 4th instance of each line by adding a number
sed 's/pattern/replacement/4'
 
# replace ALL instances of each file by adding "g"
sed 's/pattern/replacement/g'
 
# find lines that contain "foobar" and replace "pattern" with "replacement"
sed '/foobar/s/pattern/replacement/g'
 
# search "pattern" and substitute with "replacement" except lines containing "foobar"
sed '/foobar/!s/pattern/replacement/g'
 
# if you want to edit files in place, add the flag "-i"
sed -i 's/pattern/replacement/g' filename.txt
 
# replace commas with newlines (use \r, not \n)
sed 's/,/\r/g'

Selective deletion

# remove last character
sed '$s/.$//'
 
# delete last line
sed '$d'
 
# delete lines matching pattern
sed '/pattern/d'
 
# delete 2nd line
sed '2d'
 
# delete the first 10 lines
sed '1,10d'
 
# delete ALL blank lines
sed '/^$/d'

Print

# -n flag hides lines not affected by the expression, often useful in print statements
 
# print lines that contain "pattern"
sed -n '/pattern/p'
 
# print 2nd line
sed -n '2p'

Tricks

# you can perform multiple sed operations
# instead of
sed 's/foo/bar/g' | sed 's/bar/popo/g'
 
# you can do this
sed -e 's/foo/bar/g' -e 's/bar/popo/g'
 
# or even this
sed 's/foo/bar/g;s/bar/popo/g'
 
# you can substitute "/" with another character
sed 's~foo~bar~'
 
# append "foobar" after lines matching "pattern"
sed '/pattern/a foobar'
# prepend "foobar" before lines matching "pattern"
sed '/pattern/i foobar'
 
# append "foobar" after 2nd line
sed '2a foobar'
# prepend "foobar" before 2nd line
sed '2i foobar'
 
# insert 2 blank spaces at beginning of each line
sed 's/^/  /'