Useful sed

This is awkward but ...

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_NOTES
_{* This is not absolutely perfect and up to the highest standards of Posix and sed usage. It was kindly pointed to me by people from HN. I'll try and make this the best possible version I can and I'll listen to your feedback. I'm not a sed guru after all, just someone trying to follow the 20/80 formula (even though sometimes I go waaay overboard).}
_{* There is no mention of the hold space (and other registers) usage. Personally I found their usage quite confusing. If this might change in the future I'll adjust this. After all, this is not "The ultimate sed reference" but "useful sed".}
_{* There might be examples where I use -E (regexp extended option) when it is not necesarilly needed. Chances are you'll want to use this in most of your operations so it might not be a bad reflex to have. Sure, you could make an alias for it in your .bashrc. Personally I try and delay usage of aliases until I feel it's absolutely necesarry (as it hides some verbosity which makes the commands clearer).}

print one line

sed -n '10p' myfile.txt

do replacement on all lines except line 5

sed '5!/s/foo/bar/' file.txt

do replacement on lines matching regex (eg: lines starting with 'hello')

sed '/^hello/ s/h/H/' file.txt

do replacement from line 5 to end of file

sed '5,$ s/foo/bar/' file.txt

Print lines between two regexes

sed -nE '/^foo/,/^bar/p' file.txt

Use custom delimiters to make it easy for some strings that contain slashes

sed 's_/bin/bash_/bin/sh_' file.txt

Custom delimiters for regex adress combined with the classical delimiter for substitute command (you could also use there a custom delimiter). Useful for paths.

sed '\_/bin/bash_s/grep/egrep/' file.txt

or using the same delimiter for clarity sed '\_/bin/bash_s_grep_egrep_' file.txt

Insert a space between lowercase/Uppercase characters using & (which represents the regex match)

sed 's/[a-zA-Z]/& /g' file.txt

keep the first word of every line (where word is defined by alnum chars + underscores for simplicity sake)

sed -E s_[a-zA-Z0-9_]+.*_\1_' file.txt

switch the first two words

sed -E 's_([a-zA-Z0-9_]*) ([a-zA-Z0-9_]*)_\2 \1_' f1

remove duplicate words separated by a single space (but not triplicate)

sed -E 's_([a-zA-Z0-9_]+) \1_\1_ig' f1

search and replace for pattern, write just the lines with the replacements in a new file

sed 's_foo_bar_w replaced.txt' file.txt

multiple replacements

sed -e 's_foo_bar_' -e 's_hello_HELLO_' file.txt

multiple replacements by using a sed script

#!/usr/bin/sed -f
s/a/A/
s/foo/BAR/
s/hello/HELLO/

Make executable with chmod +x myscript.sed, call with ./myscript.sed myfile.txt

Multiple commands using the ; operator which in theory concatenates commands (WARNING! It won't work as expected with certain commands such as 'r' or 'w'. Use a sed script instead OR put the command dealing with filenames last). Print line 10 and insert before line 5.

sed '10p;5i\"INSERTED BEFORE LINE 5" file.txt

remove comments between lines starting with these two keywords. Empty lines will be put there instead

sed -E '/start/,/end/ s/#.*//' file.txt

Delete comments starting with # (no empty lines left behind)

sed -E '/^#/d' f1

view lines minus lines between line starting with pattern and end of file

sed '/start/,$ d' file.txt

view lines except lines between line starting with pattern and line ending with pattern

sed -rn '/start/,/end/ !p' file.txt

print until you encounter pattern then quit

sed '/start/q' file.txt

insert contents of file after a certain line

sed '5 r newfile.txt' file.txt

Append text after lines containing regex (AFTER FOO)

sed '/foo/a\AFTER FOO' file.txt

Insert text after lines containing regex (BEFORE FOO)

sed '/foo/i\BEFORE FOO' file.txt

change line containing regex match

sed '/foo/c\FOO IS CHANGED' file.txt

Nested sed ranges with inversion. Between lines 1,100 apply actions where the pattern DOESN'T match.

#!/usr/bin/sed -f
1,100 {
	/foo/ !{
		s_hello_HELLOOOOWORLD_
		s_yes_YES_
	}
}

Use nested addresses with change, insert and append to modify: the line before match, the line with match, the line after match.

#!/usr/bin/sed -f
/^#/ {
i\
#BEFFORE ORIGINAL COMMENt
a\
#AFTER ORIGINAL COMMENT
c\
# ORIGINAL COMMENT IS NOW THIS LINE
}

Insert new line before the first comment, after the first comment put in the contents of file and quit immediately afterwards

#!/usr/bin/sed -f
/^#/ {
i\#BEFORE COMMENT
r myotherfile.txt
q
}

Transform text

sed 'y/abc/ABC/' file.txt

Copy all the comments (starting with #) to a new file

sed -E '/^#/w comments.txt' file.txt

Print every second line (substitute ~3 for third line, etc)

sed '1~2p' file.txt

Edit file in place but also create a backup

sed -i.bak 's/hello/HELLO/' file.txt

robert-joscelyne / useful-sed