9.0 KiB
QSESED Commands
Overview
A stream editor is a non-interactive text editing tool commonly used on Unix environment. It reads text from an input stream, stores it to pattern space, manipulates the pattern space by applying a set of editing commands, and writes the pattern space to an output stream. Typically, the input and output streams are a console or a file.
Commands
A sed command is composed of:
- line selector (optional)
- ! (optional)
- command code
- command arguments (optional, dependent on command code)
A line selector selects input lines to apply a command to and has the following forms:
- address - specify a single address
- address,address - specify an address range
- start~step - specify a starting line and a step. #QSE_SED_EXTENDEDADR enables this form.
An address is a line number, a regular expression, or a dollar sign ($) while a start and a step is a line number.
A regular expression for an address has the following form:
- /rex/ - a regular expression rex is enclosed in slashes
- \CrexC - a regular expression rex is enclosed in \C and C where C can be any character.
It treats the \n sequence specially to match a newline character.
Here are examples of line selectors:
- 10 - match the 10th line
- 10,20 - match lines from the 10th to the 20th.
- /^:space:*$/ - match an empty line
- /^abc$/,/^def$/ - match all lines between abc and def inclusive
- 10,$ - match the 10th line down to the last line.
- 3~4 - match every 4th line from the 3rd line.
Note that an address range always selects the line matching the first address regardless of the second address; For example, 8,6 selects the 8th line.
The exclamation mark(!), when used after the line selector and before the command code, negates the line selection; For example, 1! selects all lines except the first line.
A command without a line selector is applied to all input lines; A command with a single address is applied to an input line that matches the address; A command with an address range is applied to all input lines within the range, inclusive; A command with a start and a step is applied to every step'th line starting from the line start.
Here is the summary of the commands.
# comment
The text beginning from # to the line end is ignored; # in a line following a \, i \, and c \ is treated literally and does not introduce a comment.
: label
A label can be composed of letters, digits, periods, hyphens, and underlines. It remembers a target label for b and t commands and prohibits a line selector.
{
The left curly bracket forms a command group where you can nest other commands. It should be paired with an ending }.
q
Terminates the exection of commands. Upon termination, it prints the pattern space if #QSE_SED_QUIET is not set.
Q
Terminates the exection of commands quietly.
a \ \n text
Stores text into the append buffer which is printed after the pattern space for each input line. If #QSE_SED_STRICT is on, an address range is not allowed for a line selector. If #QSE_SED_SAMELINE is on, the backslash and the text can be located on the same line without a line break.
i \ \n text
Inserts text into an insert buffer which is printed before the pattern space for each input line. If #QSE_SED_STRICT is on, an address range is not allowed for a line selector. If #QSE_SED_SAMELINE is on, the backslash and the text can be located on the same line without a line break.
c \ \n text
If a single line is selected for the command (i.e. no line selector, a single address line selector, or a start~step line selector is specified), it changes the pattern space to text and branches to the end of commands for the line. If an address range is specified, it deletes the pattern space and branches to the end of commands for all input lines but the last, and changes pattern space to text and branches to the end of commands. If #QSE_SED_SAMELINE is on, the backlash and the text can be located on the same line without a line break.
d
Deletes the pattern space and branches to the end of commands.
D
Deletes the first line of the pattern space. If the pattern space is emptied, it branches to the end of script. Otherwise, the commands from the first are reapplied to the current pattern space.
=
Prints the current line number. If #QSE_SED_STRICT is on, an address range is not allowed as a line selector.
p
Prints the pattern space.
P
Prints the first line of the pattern space.
l
Prints the pattern space in a visually unambiguous form.
h
Copies the pattern space to the hold space
H
Appends the pattern space to the hold space
g
Copies the hold space to the pattern space
G
Appends the hold space to the pattern space
x
Exchanges the pattern space and the hold space
n
Prints the pattern space and read the next line from the input stream to fill the pattern space.
N
Prints the pattern space and read the next line from the input stream to append it to the pattern space with a newline inserted.
b
Branches to the end of commands.
b label
Branches to label
t
Branches to the end of commands if substitution(s//) has been made successfully since the last reading of an input line or the last t command.
t label
Branches to label if substitution(s//) has been made successfully since the last reading of an input line or the last t command.
r file
Reads text from file and prints it after printing the pattern space but before printing the append buffer. Failure to read file does not cause an error.
R file
Reads a line of text from file and prints it after printing pattern space but before printing the append buffer. Failure to read file does not cause an error.
w file
Writes the pattern space to file
W file
Writes the first line of the pattern space to file
s/rex/repl/opts
Finds a matching substring with rex in pattern space and replaces it with repl. An ampersand(&) in repl refers to the matching substring. opts may be empty; You can combine the following options into opts:
- g replaces all occurrences of a matching substring with rex
- number replaces the number'th occurrence of a matching substring with rex
- p prints pattern space if a successful replacement was made
- w file writes pattern space to file if a successful replacement was made. It, if specified, should be the last option.
- k removes(kills) unmached portions from the pattern space. It is useful for partial extraction.
y/src/dst/
Replaces all occurrences of characters in src with characters in dst. src and dst must contain equal number of characters.
C/selector/opts
Selects characters or fields from the pattern space as specified by the selector and update the pattern space with the selected text. A selector is a comma-separated list of specifiers. A specifier is one of the followings:
- d specifies the input field delimiter with the next character. e.g) d:
- D sepcifies the output field delimiter with the next character. e.g) D;
- c specifies a position or a range of characters to select. e.g) c23-25
- f specifies a position or a range of fields to select. e.g) f1,f4-3
opts may be empty; You can combine the following options into opts:
- f folds consecutive delimiters into one.
- w uses white spaces for a field delimiter regardless of the input delimiter specified in the selector.
- d deletes the pattern space if the line is not delimited by the input field delimiter
In principle, this can replace the cut utility with the C command.
Examples
Here are some samples.
G;G;G
Triple spaces input lines. If #QSE_SED_QUIET is on, G;G;G;p. It works because the hold space is empty unless something is copied to it.
$!d
Prints the last line. If #QSE_SED_QUIET is on, try $p.
1!G;h;$!d
Prints input lines in the reverse order. That is, it prints the last line first and the first line last.
$ echo -e "a\nb\nc" | qsesed '1!G;h;$!d'
c
b
a
s/:space:{2,}/ /g
Compacts whitespaces if #QSE_SED_EXTENDEDREX is on.
s/[0-9]/&/gk
Extract all digits.
$ echo "Q123Q456" | qsesed -r 's/[0-9]+/&/gk'
123456
s/[0-9]+/&/2k
Extract the second number.
$ echo "Q123Q456" | qsesed -r 's/[0-9]+/&/2k'
456
C/d:,f3,1/
Prints the third field and the first field from a colon separated text.
$ head -5 /etc/passwd
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
sync:x:4:65534:sync:/bin:/bin/sync
$ qsesed '1,3C/d:,f3,1/;4,$d' /etc/passwd
0 root
1 daemon
2 bin