oam/knowledge base/sed.md

SED

Table of contents

1. TL;DR
2. Character classes and bracket expressions
3. Further readings
   1. Sources

TL;DR

Use character classes instead of regex shorthands.

# Quote any set of characters that is not a space.
sed -E 's|([[:graph:]]+)|"\1"|g' 'file.txt'

# Delete lines matching 'OAM' from a file.
# Overwrite the source file with the changes.
sed -i '/OAM/d' '.bash_history'

# Delete lines matching 'pattern' plus the next 5 ones.
sed '/pattern/,+5d' 'file.txt'

# Show changed fstab entries.
# Don't save the changes.
sed /etc/fstab \
  -e "s|#.*\s*/boot\s*.*|/dev/sda1  /boot  vfat   defaults             0 0|" \
  -e "s|#.*\s*ext4\s*.*|/dev/sda2  /      btrfs  compress-force=zstd  0 0|" \
  -e '/#.*\s*swap\s*.*/d'

Character classes and bracket expressions

Class	Description
[[:alnum:]]	alphanumeric characters [[:alpha:]] and [[:digit:]]; this is the same as [0-9A-Za-z] in the C locale and ASCII character
[[:alpha:]]	alphabetic characters [[:lower:]] and [[:upper:]]; this is the same as [A-Za-z] in the C locale and ASCII character encoding
[[:blank:]]	blank characters space and tab
[[:cntrl:]]	control characters; in ASCII these characters have octal codes 000 through 037 and 177 (DEL), in other character sets these are the equivalent characters, if any
[[:digit:]]	digits 0 to 9
[[:graph:]]	graphical characters [[:alnum:]] and [[:punct:]]
[[:lower:]]	lower-case letters a to z in the C locale and ASCII character encoding
[[:print:]]	printable characters [[:alnum:]], [[:punct:]] and space
[[:punct:]]	punctuation characters !, ", #, $, %, &, ', (, ), *, +, ,, -, ., /, :, ;, <, =, >, ?, @, [, \, ], ^, _, `, {, |, } and ~ in the C locale and ASCII character encoding
[[:space:]]	space characters tab, newline, vertical tab, form feed, carriage return and space in the C locale
[[:upper:]]	upper-case letters A to Z in the C locale and ASCII character encoding
[[:xdigit:]]	hexadecimal digits 0 to 9, A to F and a to f

Further readings

• GNU SED Online Tester
• Character Classes and Bracket Expressions

Sources

• sed or awk: delete n lines following a pattern