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Replacing nulls using sed
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sed(1) General Commands Manual sed(1) Name sed - stream text editor Syntax sed [-n] [-e script] [-f sfile] [file...] Description The command copies the named files (standard input default) to the standard output, edited according to a script of commands. The -f option causes the script to be taken from file sfile; these options accumulate. If there is just one -e option and no -f's, the flag -e may be omitted. The -n option suppresses the default output; inclusion in the script of a comment command of the form also suppresses the default output. (See the description of the `#' command.) A script consists of editing commands of the following form: [address [, address] ] function [arguments] Nominally, there is one command per line; but commands can be concatenated on a line by being separated with semicolons In normal operation cyclically copies a line of input into a pattern space (unless there is something left after a `D' command), applies in sequence all commands whose addresses select that pattern space, and at the end of the script copies the pattern space to the standard out- put (except under -n) and deletes the pattern space. An address is either a decimal number that counts input lines cumulatively across files, a `$' that addresses the last line of input, or a context address, `/regular expression/', in the style of ed(1) modified thus: o In a context address, the construction ?regular expression?, where ? is any character, is identical to regular expression. Note that in the context address xabcxdefx, the second x stands for itself, so that the regular expression is abcxdef. o The escape sequence ` ' matches a new line embedded in the pattern space. o A command line with no addresses selects every pattern space. o A command line with one address selects each pattern space that matches the address. o A command line with two addresses selects the inclusive range from the first pattern space that matches the first address through the next pattern space that matches the second. (If the second address is a number less than or equal to the line number first selected, only one line is selected.) Thereafter the process is repeated, looking again for the first address. Editing commands can be applied only to non-selected pattern spaces by use of the negation function `!' (below). In the following list of functions the maximum number of permissible addresses for each function is indicated in parentheses. An argument denoted text consists of one or more lines, all but the last of which end with `' to hide the new line. Backslashes in text are treated like backslashes in the replacement string of an `s' command, and may be used to protect initial blanks and tabs against the stripping that is done on every script line. An argument denoted rfile or wfile must terminate the command line and must be preceded by exactly one blank. Each wfile is created before processing begins. There can be at most 10 distinct wfile arguments. (1)a text Append. Place text on the output before reading the next input line. (2)b label Branch to the `:' command bearing the label. If label is empty, branch to the end of the script. (2)c text Change. Delete the pattern space. With 0 or 1 address or at the end of a 2-address range, place text on the output. Start the next cycle. (2)d Delete the pattern space. Start the next cycle. (2)D Delete the initial segment of the pattern space through the first new line. Start the next cycle. (2)g Replace the contents of the pattern space by the contents of the hold space. (2)G Append the contents of the hold space to the pattern space. (2)h Replace the contents of the hold space by the contents of the pattern space. (2)H Append the contents of the pattern space to the hold space. (1)i text Insert. Place text on the standard output. (2)n Copy the pattern space to the standard output. Replace the pattern space with the next line of input. (2)N Append the next line of input to the pattern space with an embedded new line. (The current line number changes.) (2)p Print. Copy the pattern space to the standard output. (2)P Copy the initial segment of the pattern space through the first new line to the standard output. (1)q Quit. Branch to the end of the script. Do not start a new cycle. (2)r rfile Read the contents of rfile. Place them on the output before reading the next input line. (2)s/regular expression/replacement/flags Substitute the replacement string for instances of the regular expression in the pattern space. Any character may be used instead of `/'. For a more complete description see The flags is zero or more of g Global. Substitute for all nonoverlapping instances of the regular expression rather than just the first one. p Print the pattern space if a replacement was made. w wfile Write. Append the pattern space to wfile if a replacement was made. (2)t label Test. Branch to the `:' command bearing the label if any substitutions have been made since the most recent reading of an input line or execution of a `t'. If label is empty, branch to the end of the script. (2)w wfile Write. Append the pattern space to wfile. (2)x Exchange the contents of the pattern and hold spaces. (2)y/string1/string2/ Transform. Replace all occurrences of characters in string1 with the corresponding character in string2. The lengths of string1 and string2 must be equal. (2)! function Don't. Apply the function (or group, if function is `{') only to lines not selected by the address(es). (0): label This command does nothing; it bears a label for `b' and `t' commands to branch to. (1)= Place the current line number on the standard output as a line. (2){ Execute the following commands through a matching `}' only when the pattern space is selected. (0) An empty command is ignored. (0)# With one exception, any line whose first nonblank character is a number sign is a comment and is ignored. The exception is that if the first such line encountered contains only the number sign followed by the letter `n' the default output is suppressed as if the -n option were in force. Options -e 'command;command...' Uses command;command... as the editing script. If no -f option is given, the -e keyword can be omitted. For example, the follow- ing two command are functionally identical: % sed -e 's/DIGITAL/Digital/g' summary > summary.out % sed 's/DIGITAL/Digital/g' summary > summary.out -f sfile Uses specified file as input file of commands to be executed. Can be used with -e option to apply both explicit commands and a separate script file. -n Suppresses all normal output, writing only lines explicitly written by the `p' or `P' commands or by an `s' command with the `p' flag. See Also awk(1), ed(1), grep(1), lex(1) sed(1)
