3.1.4. Command-line switches

All versions of sed support two switches, -e and -n. Though sed usually separates multiple commands with semicolons (e.g., "H;d;"), certain commands could not accept a semicolon command separator. These include :labels, 't', and 'b'. These commands had to occur last in a script, separated by -e option switches. For example:

     # The 'ta' means jump to label :a if last s/// returns true
     sed -e :a -e '$!N;s/\n=/ /;ta' -e 'P;D' file

The -n switch turns off sed's default behavior of printing every line. With -n, lines are printed only if explicitly told to. In addition, for certain versions of sed, if an external script begins with "#n" as its first two characters, the output is suppressed (exactly as if -n had been entered on the command line). A list of which versions appears in section 6.7.2., below.

GNU sed 4.x and ssed support additional switches. -l (lowercase L), followed by a number, lets you adjust the default length of the 'l' and 'L' commands (note that these implementations of sed also support an argument to these commands, to tailor the length separately of each occurrence of the command).

-i activates in-place editing (see section 4.41.1, below). -s treats each file as a separate stream: sed by default joins all the files, so $ represents the last line of the last file; 15 means the 15th line in the joined stream; and /abc/,/def/ might match across files.

When -s is used, however all addresses refer to single files. For example, $ represents the last line of each input file; 15 means the 15th line of each input file; and /abc/,/def/ will be "reset" (in other words, sed will not execute the commands and start looking for /abc/ again) if a file ends before /def/ has been matched. Note that -i automatically activates this interpretation of addresses.