$FreeBSD: src/bin/ed/POSIX,v 1.8 2000/07/17 10:40:48 sheldonh Exp $ This version of ed(1) is not strictly POSIX compliant, as described in the POSIX 1003.2 document. The following is a summary of the omissions, extensions and possible deviations from POSIX 1003.2. OMISSIONS --------- 1) For backwards compatibility, the POSIX rule that says a range of addresses cannot be used where only a single address is expected has been relaxed. 2) To support the BSD `s' command (see extension  below), substitution patterns cannot be delimited by numbers or the characters `r', `g' and `p'. In contrast, POSIX specifies any character expect space or newline can used as a delimiter. EXTENSIONS ---------- 1) BSD commands have been implemented wherever they do not conflict with the POSIX standard. The BSD-ism's included are: i) `s' (i.e., s[n][rgp]*) to repeat a previous substitution, ii) `W' for appending text to an existing file, iii) `wq' for exiting after a write, iv) `z' for scrolling through the buffer, and v) BSD line addressing syntax (i.e., `^' and `%') is recognized. 2) If crypt(3) is available, files can be read and written using DES encryption. The `x' command prompts the user to enter a key used for encrypting/ decrypting subsequent reads and writes. If only a newline is entered as the key, then encryption is disabled. Otherwise, a key is read in the same manner as a password entry. The key remains in effect until encryption is disabled. For more information on the encryption algorithm, see the bdes(1) man page. Encryption/decryption should be fully compatible with SunOS des(1). 3) The POSIX interactive global commands `G' and `V' are extended to support multiple commands, including `a', `i' and `c'. The command format is the same as for the global commands `g' and `v', i.e., one command per line with each line, except for the last, ending in a backslash (\). 4) An extension to the POSIX file commands `E', `e', `r', `W' and `w' is that <file> arguments are processed for backslash escapes, i.e., any character preceded by a backslash is interpreted literally. If the first unescaped character of a <file> argument is a bang (!), then the rest of the line is interpreted as a shell command, and no escape processing is performed by ed. 5) For SunOS ed(1) compatibility, ed runs in restricted mode if invoked as red. This limits editing of files in the local directory only and prohibits shell commands. DEVIATIONS ---------- 1) Though ed is not a stream editor, it can be used to edit binary files. To assist in binary editing, when a file containing at least one ASCII NUL character is written, a newline is not appended if it did not already contain one upon reading. In particular, reading /dev/null prior to writing prevents appending a newline to a binary file. For example, to create a file with ed containing a single NUL character: $ ed file a ^@ . r /dev/null wq Similarly, to remove a newline from the end of binary `file': $ ed file r /dev/null wq 2) Since the behavior of `u' (undo) within a `g' (global) command list is not specified by POSIX, it follows the behavior of the SunOS ed: undo forces a global command list to be executed only once, rather than for each line matching a global pattern. In addtion, each instance of `u' within a global command undoes all previous commands (including undo's) in the command list. This seems the best way, since the alternatives are either too complicated to implement or too confusing to use. The global/undo combination is useful for masking errors that would otherwise cause a script to fail. For instance, an ed script to remove any occurences of either `censor1' or `censor2' might be written as: ed - file <<EOF 1g/.*/u\ ,s/censor1//g\ ,s/censor2//g ... 3) The `m' (move) command within a `g' command list also follows the SunOS ed implementation: any moved lines are removed from the global command's `active' list. 4) If ed is invoked with a name argument prefixed by a bang (!), then the remainder of the argument is interpreted as a shell command. To invoke ed on a file whose name starts with bang, prefix the name with a backslash.