SED Addressing, Regular Expressions, Bugs, Author, and See Also

to the second address. Three things to note about address ranges: the syntax is addr1,addr2 (i.e., the addresses are separated by a comma); the line which addr1 matched will always be accepted, even if addr2 selects an earlier line; and if addr2 is a regexp, it will not be tested against the line that addr1 matched. After the address (or address‐range), and before the command, a ! may be inserted, which specifies that the command shall only be executed if the address (or address‐range) does not match. The following address types are supported: number Match only the specified line number (which increments cumula‐ tively across files, unless the -s option is specified on the command line). first~step Match every step’th line starting with line first. For example, ‘‘sed -n 1~2p’’ will print all the odd‐numbered lines in the in‐ put stream, and the address 2~5 will match every fifth line, starting with the second. first can be zero; in this case, sed operates as if it were equal to step. (This is an extension.) $ Match the last line. /regexp/ Match lines matching the regular expression regexp. Matching is performed on the current pattern space, which can be modified with commands such as ‘‘s///’’. \cregexpc Match lines matching the regular expression regexp. The c may be any character. GNU sed also supports some special 2‐address forms: 0,addr2 Start out in "matched first address" state, until addr2 is found. This is similar to 1,addr2, except that if addr2 matches the very first line of input the 0,addr2 form will be at the end of its range, whereas the 1,addr2 form will still be at the beginning of its range. This works only when addr2 is a regular expression. addr1,+N Will match addr1 and the N lines following addr1. addr1,~N Will match addr1 and the lines following addr1 until the next line whose input line number is a multiple of N. REGULAR EXPRESSIONS POSIX.2 BREs should be supported, but they aren’t completely because of performance problems. The \n sequence in a regular expression matches the newline character, and similarly for \a, \t, and other sequences. The ‐E option switches to using extended regular expressions instead; it has been supported for years by GNU sed, and is now included in POSIX. BUGS E‐mail bug reports to bug‐sed@gnu.org. Also, please include the output of ‘‘sed --version’’ in the body of your report if at all possible. AUTHOR Written by Jay Fenlason, Tom Lord, Ken Pizzini, Paolo Bonzini, Jim Mey‐ ering, and Assaf Gordon. This sed program was built with SELinux support. SELinux is disabled on this system. GNU sed home page: <https://www.gnu.org/software/sed/>. General help using GNU software: <https://www.gnu.org/gethelp/>. E-mail bug reports to: <bug-sed@gnu.org>. SEE ALSO awk(1), ed(1), grep(1), tr(1), perlre(1), sed.info, any of various books on sed, the sed FAQ (http://sed.sf.net/grabbag/tutorials/sedfaq.txt), http://sed.sf.net/grabbag/. The full documentation for sed is maintained as a Texinfo manual. If the info and sed programs are properly installed at your site, the com‐ mand info sed should give you access to the complete manual. GNU sed 4.9 January 2023 SED(1)

This section continues the discussion of addressing in `sed`, covering address types such as matching the last line (`$`), regular expressions (`/regexp/`, `\cregexpc`), and special 2-address forms (`0,addr2`, `addr1,+N`, `addr1,~N`). It then briefly mentions regular expressions, noting POSIX.2 BRE support (though incomplete) and the \n sequence. It mentions that the -E option enables extended regular expressions. The document then provides information on reporting bugs, the authors of GNU sed, and links to the GNU sed home page and general help resources. Finally, it lists related commands and documentation, including `awk`, `ed`, `grep`, `tr`, `perlre`, the sed FAQ, and the sed manual accessible via `info sed`.