Interpret regular expressions as extended (modern) regular expressions rather than basic regular expressions (BREs). The re_format(7) manual page fully describes both formats.
The files listed as parameters for the "w" functions are created (or truncated) before any processing begins, by default. The -a option causes sed to delay opening each file until a command containing the related "w" function is applied to a line of input.
Append the editing commands specified by the command argument to the list of commands.
Append the editing commands found in the file command_file to the list of commands. The editing commands should each be listed on a separate line.
Edit files in-place, saving backups with the specified extension. If a zero-length extension is given, no backup will be saved. It is not recommended to give a zero-length extension when in-place editing files, as you risk corruption or partial content in situations where disk space is exhausted, etc.
Make output line buffered.
By default, each line of input is echoed to the standard output after all of the commands have been applied to it. The -n option suppresses this behavior.
The form of a sed command is as follows:
Whitespace may be inserted before the first address and the function portions of the command.
Normally, sed cyclically copies a line of input, not including its terminating newline character, into a "pattern space", (unless there is something left after a "D" function), applies all of the commands with addresses that select that pattern space, copies the pattern space to the standard output, appending a newline, and deletes the pattern space.
Some of the functions use a "hold space" to save all or part of the pattern space for subsequent retrieval.
Execute function-list only when the pattern space is selected.
Write text to standard output immediately before each attempt to read a line of input, whether by executing the "N" function or by beginning a new cycle.
Branch to the ":" function with the specified label. If the label is not specified, branch to the end of the script.
Delete the pattern space. With 0 or 1 address or at the end of a 2-address range, text is written to the standard output.
Delete the pattern space and start the next cycle.
Delete the initial segment of the pattern space through the first newline character and start the next cycle.
Replace the contents of the pattern space with the contents of the hold space.
Append a newline character followed by the contents of the hold space to the pattern space.
Replace the contents of the hold space with the contents of the pattern space.
Append a newline character followed by the contents of the pattern space to the hold space.
Write text to the standard output.
(The letter ell.) Write the pattern space to the standard output in a visually unambiguous form. This form is as follows:
Nonprintable characters are written as three-digit octal numbers (with a preceding backslash) for each byte in the character (most significant byte first). Long lines are folded, with the point of folding indicated by displaying a backslash followed by a newline. The end of each line is marked with a "$".
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.
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.
Write the pattern space to standard output.
Write the pattern space, up to the first newline character to the standard output.
Branch to the end of the script and quit without starting a new cycle.
Copy the contents of file to the standard output immediately before the next attempt to read a line of input. If file cannot be read for any reason, it is silently ignored and no error condition is set.
Substitute the replacement string for the first instance of the regular expression in the pattern space. Any character other than backslash or newline can be used instead of a slash to delimit the RE and the replacement. Within the RE and the replacement, the RE delimiter itself can be used as a literal character if it is preceded by a backslash.
An ampersand ("&") appearing in the replacement is replaced by the string matching the RE. The special meaning of "&" in this context can be suppressed by preceding it by a backslash. The string "\#", where "#" is a digit, is replaced by the text matched by the corresponding backreference expression (see re_format(7)).
A line can be split by substituting a newline character into it. To specify a newline character in the replacement string, precede it with a backslash.
The value of flags in the substitute function is zero or more of the following:
Make the substitution only for the N th occurrence of the regular expression in the pattern space.
Make the substitution for all non-overlapping matches of the regular expression, not just the first one.
Write the pattern space to standard output if a replacement was made. If the replacement string is identical to that which it replaces, it is still considered to have been a replacement.
Append the pattern space to file if a replacement was made. If the replacement string is identical to that which it replaces, it is still considered to have been a replacement.
Branch to the ":" function bearing the label if any substitutions have been made since the most recent reading of an input line or execution of a "t" function. If no label is specified, branch to the end of the script.
Append the pattern space to the file.
Swap the contents of the pattern and hold spaces.
Replace all occurrences of characters in string1 in the pattern space with the corresponding characters from string2. Any character other than a backslash or newline can be used instead of a slash to delimit the strings. Within string1 and string2, a backslash followed by any character other than a newline is that literal character, and a backslash followed by an n is replaced by a newline character.
Apply the function or function-list only to the lines that are not selected by the address(es).
This function does nothing; it bears a label to which the "b" and "t" commands may branch.
Write the line number to the standard output followed by a newline character.
Empty lines are ignored.
The "#" and the remainder of the line are ignored (treated as a comment), with the single exception that if the first two characters in the file are "#n", the default output is suppressed. This is the same as specifying the -n option on the command line.