shellScripting/learnsed.sed

#!/usr/bin/sed -f
# Files that begin with the above line and are given execute permission
# can be run as regular scripts.

# Comments are like this.

# Commands consist of a single letter and many can be preceded
# by a specification of the lines to which they apply.

# Delete the input's third line.
3d

# The same command specified the command line as an argument to sed:
# sed 3d

# For many commands the specification can consist of two addresses,
# which select an inclusive range.
# Addresses can be specified numerically ($ is the last line) or through
# regular expressions delimited by /.

# Delete lines 1-10
1,10d

# Lines can also be specified as regular expressions, delimited by /.

# Delete empty lines.
/^$/d

# Delete blocks starting with SPOILER-BEGIN and ending with SPOILER-END.
/SPOILER-BEGIN/,/SPOILER-END/d

# A command without an address is applied to all lines.

# List lines in in a visually unambiguous form (e.g. tab appears as \t).
l

# A command prefixed by ! will apply to non-matching lines.
# Keep only lines starting with a #.
/^#/!d

# Below are examples of the most often-used commands.

# Substitute the first occurrence in a line of John with Mary.
s/John/Mary/

# Remove all underscore characters (global substitution).
s/_//g

# Remove all HTML tags.
s/<[^>]*>//g

# In the replacement string & is the regular expression matched.

# Put each line inside double quotes.
s/.*/"&"/

# In the matched regular expression \(pattern\) is used to store
# a pattern into a buffer.
# In the replacement string \1 refers to the first pattern, \2 to the second
# and so on. \u converts the following character to uppercase \l to lowercase.

# Convert snake_case_identifiers into camelCaseIdentifiers.
s/_\(.\)/\u\1/g


# The p (print) command is typically used together with the -n
# command-line option, which disables the print by default functionality.
# Output all lines between ``` and ```.
/```/,/```/p


# The y command maps characters from one set to another.
# Swap decimal and thousand separators (1,234,343.55 becomes 1.234.343,55).
y/.,/,./

# Quit after printing the line starting with END.
/^END/q

# You can stop reading here, and still get 80% of sed's benefits.
# Below are examples of how you can specify multiple sed commands.

# You can apply multiple commands by separating them with a newline or
# a semicolon.

# Delete the first and the last line.
1d
$d

# Delete the first and the last line.
1d;$d


# You can group commands in { } blocks.

# Convert first line to uppercase and print it.
1 {
  s/./\u&/g
  p
}

# Convert first line to uppercase and print it (less readable one-liner).
1{s/./\u&/g;p;}


# You can also stop reading here, if you're not interested in creating
# sed script files.

# Below are more advanced commands.  You typically put these in a file
# rather than specify them on a command line.  If you have to use
# many of these commands in a script, consider using a general purpose
# scripting language, such as Python or Perl.

# Append a line containing "profile();" after each line ending with ";".
/;$/a\
profile();

# Insert a line containing "profile();" before each line ending with ";".
/;$/i\
profile();

# Change each line text inside REDACTED blocks into [REDACTED].
/REDACTED-BEGIN/,/REDACTED-END/c\
[REDACTED]

# Replace the tag "<ourstyle>" by reading and outputting the file style.css.
/<ourstyle>/ {
  r style.css
  d
}

# Change each line inside REDACTED blocks into [REDACTED].
# Also write (append) a copy of the redacted text in the file redacted.txt.
/REDACTED-BEGIN/,/REDACTED-END/ {
  w redacted.txt
  c\
  [REDACTED]
}

# All operations described so far operate on a buffer called "pattern space".
# In addition, sed offers another buffer called "hold space".
# The following commands operate on the two, and can be used to keep
# state or combine multiple lines.

# Replace the contents of the pattern space with the contents of
# the hold space.
g

# Append a newline character followed by the contents of the hold
# space to the pattern space.
G

# Replace the contents of the hold space with the contents of the
# pattern space.
h

# Append a newline character followed by the contents of the
# pattern space to the hold space.
H

# Delete the initial segment of the pattern space through the first
# newline character and start the next cycle.
D

# Replace the contents of the pattern space with the contents of
# the hold space.
g

# Append a newline character followed by the contents of the hold
# space to the pattern space.
G

# Replace the contents of the hold space with the contents of the
# pattern space.
h

# Append a newline character followed by the contents of the
# pattern space to the hold space.
H

# Write the pattern space to the standard output if the default
# output has not been suppressed, and replace the pattern space
# with the next line of input.
n

# Append the next line of input to the pattern space, using an
# embedded newline character to separate the appended material from
# the original contents.  Note that the current line number
# changes.
N

# Write the pattern space, up to the first newline character to the
# standard output.
P

# Swap the contents of the pattern and hold spaces.
x

# Here is a complete example of some of the buffer commands.
# Move the file's first line to its end.
1 {
  h
  d
}

$ {
  p
  x
}


# Three sed commands influence a script's control flow

# Name this script position "my_label", to which the "b" and
# "t" commands may branch.
:my_label

# Continue executing commands from the position of my_label.
b my_label

# Branch to the end of the script.
b

# Branch to my_label if any substitutions have been made since the most
# recent reading of an input line or execution of a "t" (test) function.
t my_label

# Here is a complete example of branching:
# Join lines that end with a backslash into a single space-separated one.

# Name this position "loop"
: loop
# On lines ending with a backslash
/\\$/ {
  # Read the next line and append it to the pattern space
  N
  # Substitute backslash newline with a space
  s/\\\n/ /
  # Branch to the top for testing this line's ending
  b loop
}