OSF

NAME

sed − Provides a stream line editor

SYNOPSIS

sed [−n] [−e script ...] [−f source-file] [file ...]

sed [−n] [script] [file ...]

The sed command modifies lines from the specified file or from standard input according to edit commands and writes them to standard output. 

FLAGS

-e scriptUses the string script as an editing script.  If you are using just one -e flag and no -f flag, you can omit the -e flag and include the single script on the command line as an argument to sed. 

-f source_file
Uses source_file as the source of the edit script.  The source_file is a set of editing commands to be applied to file. 

-nSuppresses all information normally written to standard output. 

DESCRIPTION

The sed command includes many features for selecting lines to be modified and making changes only to the selected lines. 

The sed command uses two work spaces for holding the line being modified:  the pattern space, where the selected line is held, and the hold space, where a line can be stored temporarily. 

An edit script consists of individual subcommands, each one on a separate line.  The general form of sed subcommands is as follows:

[address_range] function [modifier ...]

The sed command processes each input file by reading an input line into a pattern space, sequentially applying all sed subcommands in sequence whose addresses select that line, and writing the pattern space to standard output.  It then clears the pattern space and repeats this process for each line in the input file.  Some of the subcommands use a hold space to save all or part of the pattern space for subsequent retrieval. 

When a command includes an address, either a line number or a search pattern, only the addressed line or lines are affected by the command.  Otherwise, the command is applied to all lines. 

sed Addresses

An address is either a decimal line number, a $, which addresses the last line of input, or a context address.  A context address is a regular expression as described for grep, except that you can select the character delimiter for patterns.  The general form of the expression is as follows:

\?pattern\?

The ? represents a character delimiter you select.  This delimiter cannot be a 2-byte international character support extended character. 

The default form for the pattern is as follows:

/pattern/

       •The sequence \n matches a newline character in the pattern space, except the terminating new line. 

       •A . (dot) matches any character except a terminating newline character.  That is, unlike grep, which cannot match a newline character in the middle of a line, sed can match a newline character in the pattern space. 

Certain commands allow you to specify one line or a range of lines to which the command applies.  These commands are called addressed commands.  The following rules apply to addressed commands:

       •A command line with no address selects every line. 

       •A command line with one address, expressed in context form, selects each line that matches the address. 

       •A command line with two addresses separated by a , (comma) or ; (semicolon) selects the entire range from the first line that matches the first address through the next line 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. 

SUBCOMMANDS

Backslashes in text are treated like backslashes in the replacement string of an s command and can be used to protect initial spaces and tabs against the stripping that is done on every script line. 

The text argument accompanying the a\, c\, and i\ commands can continue onto more than one line, provided all lines but the last end with a \ (backslash) to quote the newline character. 

The read_file and write_file arguments must end the command line and must be preceded by exactly one space.  Each write_file is created before processing begins. 

The sed command can process up to 99 commands in a file. 

In the following list of subcommands, the maximum number of permissible addresses for each subcommand is indicated in parentheses.  The sed script subcommands are as follows:

(1) a\

textPlaces text on the output before reading the next input line. 

(2)b[label]
Branches to the : command bearing the label.  If label is empty, it branches to the end of the script. 

(2)c\

textDeletes the pattern space.  With a 0 or 1 address or at the end of a 2-address range, places text on the output.  Then it starts the next cycle. 

(2)dDeletes the pattern space.  Then it starts the next cycle. 

(2)DDeletes the initial segment of the pattern space through the first newline character.  Then it starts the next cycle. 

(2)gReplaces the contents of the pattern space with the contents of the hold space. 

(2)GAppends the contents of the hold space to the pattern space. 

(2)hReplaces the contents of the hold space with the contents of the pattern space. 

(2)HAppends the contents of the pattern space to the hold space. 

(1)i\

textWrites text to standard output before reading the next line into the pattern space. 

(2)lWrites the pattern space to standard output, showing nondisplayable characters as 2- or 4-digit hexadecimal values.  Long lines are folded. 

(2)nWrites the pattern space to standard output.  It replaces the pattern space with the next line of input. 

(2)NAppends the next line of input to the pattern space with an embedded newline character.  (The current line number changes.)  You can use this to search for patterns that are split onto two lines. 

(2)pWrites the pattern space to standard output. 

(2)PWrites the initial segment of the pattern space through the first newline character to standard output. 

(1)qBranches to the end of the script.  It does not start a new cycle. 

(1)r read_file
Reads the contents of read_file.  It places contents on the output before reading the next input line. 

(2)s/pattern/replacement/flags
Substitutes the replacement string for the first occurrence of the pattern in the pattern space.  Any character that is displayed after the s command can substitute for the / (slash) separator.  For Japanese Language Support: Any single-byte character appearing after the s can substitute for the / (slash) separator.  You can add zero or more of the following flags:

nWhere n is 1-512, substitutes replacement for the nth occurence of pattern on each addressed line, rather than for the first occurence. 

gSubstitutes replacement for all nonoverlapping instances of pattern on each addressed line, rather than for just the first one (or for the one specified by n). 

pWrites the pattern space to standard output if a replacement was made. 

w write_file
Writes the pattern space to write_file if a replacement was made.  Appends the pattern space to write_file.  If write_file was not already created by a previous write by this sed script, sed creates it.  Each write_file is created before processing begins. 

(2)t[label]
Branches to :label in the script file if any substitutions were made since the most recent reading of an input line execution of a t subcommand.  If you do not specify label, control transfers to the end of the script. 

(2)w write_file
Appends the pattern space to write_file. 

(2)xExchanges the contents of the pattern space and the hold space. 

(2)y/pattern1/pattern2/
Replaces all occurrences of characters in pattern1 with the corresponding characters from pattern2.  The byte lengths of pattern1 and pattern2 must be equal. 

(2)!sed_command
Applies the specified sed subcommand only to lines not selected by the address or addresses. 

(0):labelThis script entry simply marks a branch point to be referenced by the b and t commands.  This label can be any sequence of eight or fewer bytes. 

(1)=Writes the current line number to standard output as a line. 

(2){subcommand ...

}Groups subcommands enclosed in { } (braces). 

(0)Ignores an empty command. 

(0)#If a # (number sign) appears as the first character on the first line of a script file, that entire line is treated as a comment, with one exception.  If the character after the # is an n, the default output is suppressed.  The rest of the line after the #n is ignored.  A script must contain at least one noncomment line. 

EXAMPLES

     1.To perform a global change, enter:

sed  "s/happy/enchanted/g"  chap1  >chap1.new

This replaces each occurrence of happy found in the file chap1 with enchanted, and puts the edited version in a separate file named chap1.new.  The g at the end of the s subcommand tells sed to make as many substitutions as possible on each line.  Without the g, sed replaces only the first happy on a line.  The sed stream editor operates as a filter.  It reads text from standard input or from the files named on the command line (chap1 in this example), modifies this text, and writes it to standard output.  Unlike most editors, it does not replace the original file.  This makes sed a powerful command when used in pipelines. 

     2.To use sed as a filter in a pipeline (sh only), enter:

pr  chap2 | sed  "s/Page  ∗[0-9]∗$/(&)/" | print

This encloses the page numbers in parentheses before printing chap2.  The pr command puts a heading and page number at the top of each page, then sed puts the page numbers in parentheses, and the print command prints the edited listing.  The sed pattern /Page ∗[0-9]∗$/ matches page numbers that appear at the end of a line.  The s subcommand changes this to (&), where the & stands for the pattern that was matched (for example, Page  5). 

     3.To display selected lines of a file, enter:

sed  -n  "/food/p" chap3

This displays each line in chap3 that contains the word food.  Normally, sed copies every line to standard output after it is edited.  The -n flag stops sed from doing this.  You then use subcommands like p to write specific parts of the text.  Without the -n, this example displays all the lines in chap3, and it shows each line containing food twice. 

     4.To perform complex editing, enter:

sed  -f  script.sed  chap4  >chap4.new

It is always a good idea to create a sed script file when you want to do anything complex.  You can then test and modify your script before using it.  You can also reuse your script to edit other files.  Create the script file with an interactive text editor. 

     5.A sample sed script follows:

:join
/\\$/{N
s/\\\n//
b join
}

This sed script joins each line that ends with a \ (backslash) to the line that follows it.  First, the pattern /\\$/ selects a line that ends with a \ for the group of commands enclosed in { }.  The N subcommand then appends the next line, embedding a newline character.  The s/\\\n// deletes the \ (backslash) and embedded newline character.  Finally, b join branches back to the label :join to check for a \ (backslash) at the end of the newly joined line.  Without the branch, sed writes the joined line and reads the next one before checking for a second \ character.  The N subcommand causes sed to stop immediately if there are no more lines of input (that is, if N reads the End-of-File character).  It does not copy the pattern space to standard output before stopping.  This means that if the last line of the input ends with a \ (backslash) character, then it is not copied to the output. 

RELATED INFORMATION

Commands:  awk(1), grep(1)/egrep(1)/fgrep(1), vi(1)/vedit(1)/view(1). 

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