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Comandos Linux – Comando sed

Comando Linux sed

comando sed

Em sistemas operacionais do tipo Unix, sed é um editor de fluxo : filtra e transforma texto .

Este documento cobre a versão GNU / Linux do sed .

Descrição

sed é um editor de stream . Um editor de fluxo é usado para executar transformações básicas de texto em um fluxo de entrada (um arquivo ou entrada de um pipeline ). Embora, de certa forma, semelhante a um editor que permita edições com script (como ed ), o sed funcione fazendo apenas uma passagem sobre a (s) entrada (s) e, consequentemente, seja mais eficiente. Mas é a capacidade do sed de filtrar texto em um pipeline que o distingue particularmente de outros tipos de editores.

Sintaxe

OPÇÕES sed ... [ SCRIPT ] [ INPUTFILE ...]

Se você não especificar INPUTFILE , ou se INPUTFILE for ”  “, sed filtra o conteúdo da entrada padrão . O script é, na verdade, o primeiro parâmetro não opcional , que sed considera especialmente um script e não um arquivo de entrada se e somente se nenhuma das outras opções especificar um script a ser executado (ou seja, se nenhuma das opções -e e -f opções está especificada).

Opções

-n , –quiet , –silentSuprima a impressão automática do espaço do padrão.
-e script , –expression = scriptAdicione o script script aos comandos a serem executados.
-f arquivo de script , –file = arquivo de scriptAdicione o conteúdo do arquivo de script aos comandos a serem executados.
–follow-symlinksSiga os links simbólicos ao processar no local.
-i [ SUFIXO ], – in-loco [ SUFIXO ]Edite os arquivos no local (isso faz um backup com a extensão de arquivo SUFFIX , se SUFFIX for fornecido).
-l N , – comprimento da linha = NEspecifique o comprimento de quebra de linha desejado, N , para o comando ” l “.
–POSIXDesative todas as extensões GNU .
-r , –regexp-extendedUse expressões regulares estendidas no script.
-s , –separateConsidere os arquivos como separados e não como um único fluxo longo contínuo.
-u , –unfufferedCarregue quantidades mínimas de dados dos arquivos de entrada e limpe os buffers de saída com mais frequência.
–SocorroExiba uma mensagem de ajuda e saia.
–versãoInformações de versão de saída e saída.

Sed programas

Um programa sed consiste em um ou mais comandos sed , passados ​​por uma ou mais das opções -e , -f , –expression e –file , ou o primeiro argumento de não opção, se nenhuma dessas opções for usada. Esta documentação freqüentemente se refere ao ” sed ” script; isso deve ser entendido como a catenação em ordem de todos os scripts e arquivos de script transmitidos.

Os comandos em um script ou arquivo de script podem ser separados por ponto e vírgula (” ; “) ou novas linhas ( código ASCII 10). Alguns comandos, devido à sua sintaxe , não podem ser seguidos por ponto-e-vírgula trabalhando como separadores de comando e, portanto, devem ser finalizados com novas linhas ou ser colocados no final de um script ou arquivo de script. Os comandos também podem ser precedidos com caracteres de espaço em branco não significativos opcionais .

Cada comando sed consiste em um endereço ou intervalo de endereços opcional (por exemplo, números de linha que especificam em qual parte do arquivo operar; consulte Selecionando Linhas para obter detalhes), seguido por um nome de comando de um caractere e qualquer código adicional específico de comando.

Como funciona o sed

O sed mantém dois buffers de dados: o espaço padrão ativo e o espaço de retenção auxiliar . Ambos estão inicialmente vazios.

sed opera executando o seguinte ciclo em cada linha de entrada: primeiro, sed lê uma linha do fluxo de entrada, remove qualquer nova linha à direita e a coloca no espaço do padrão. Então os comandos são executados; cada comando pode ter um endereço associado a ele: os endereços são um tipo de código de condição e um comando é executado apenas se a condição for verificada antes da execução do comando.

Quando o final do script é atingido, a menos que a opção -n esteja em uso, o conteúdo do espaço do padrão é impresso no fluxo de saída, adicionando novamente a nova linha à direita se ela tiver sido removida. Em seguida, o próximo ciclo inicia para a próxima linha de entrada.

A menos que comandos especiais (como ‘ D ‘) sejam usados, o espaço do padrão é excluído entre dois ciclos. O espaço de espera, por outro lado, mantém seus dados entre os ciclos (consulte os comandos ‘ h ‘, ‘ H ‘, ‘ x ‘, ‘ g ‘, ‘ G ‘ para mover dados entre os dois buffers).

Selecionando linhas com sed

Os endereços em um script sed podem estar em qualquer uma das seguintes formas:

númeroA especificação de um número de linha corresponderá apenas a essa linha na entrada. (Observe que sed conta linhas continuamente em todos os arquivos de entrada, a menos que as opções -i ou -s sejam especificadas.)
primeiro passoEsta extensão GNU do sed corresponde a todas as linhas de passo que começam com a linha primeiro . Em particular, as linhas serão selecionadas quando existir um n não negativo, de modo que o número da linha atual seja igual a primeiro + ( n * etapa ). Assim, para selecionar as linhas com números ímpares, usaria-se 1 ~ 2 ; para escolher cada terceira linha que começa com a segunda, ‘ 2 ~ 3 ‘ seria usado; para escolher cada quinta linha que começa com a décima, use ’10 ~ 5 ‘; e ’50 ~ 0 ‘ é apenas outra maneira de dizer 50 .
$Este endereço corresponde à última linha do último arquivo de entrada ou à última linha de cada arquivo quando as opções -i ou -s são especificadas.
regexp /Isso selecionará qualquer linha que corresponda à expressão regular regexp . Se o próprio regexp incluir caracteres ” / “, cada um deverá ser escapado por uma barra invertida (” \ “).

A expressão regular vazia ‘ // ‘ repete a última correspondência de expressão regular (o mesmo vale se a expressão regular vazia for passada para o comando s). Observe que modificadores para expressões regulares são avaliados quando a expressão regular é compilada; portanto, é inválido especificá-los juntamente com a expressão regular vazia.

regexp %(The % may be replaced by any other single character.)

This also matches the regular expression regexp, but allows one to use a different delimiter than “/“. This option is particularly useful if the regexp itself contains a lot of slashes, since it avoids the tedious escaping of every “/“. If regexp itself includes any delimiter characters, each must be escaped by a backslash (“\“).

/regexp/I

\%regexp%I

The I modifier to regular-expression matching is a GNU extension which causes the regexp to be matched in a case-insensitive (as opposed to case-sensitive) manner.
/regexp/M

\%regexp%M

The M modifier to regular-expression matching is a GNU sed extension which causes ^ and $ to match respectively (in addition to the normal behavior) the empty string after a newline, and the empty string before a newline. There are special character sequences (“\`” and “\’“) which always match the beginning or the end of the buffer. M stands for multi-line.

If no addresses are given, then all lines are matched; if one address is given, then only lines matching that address are matched.

An address range can be specified by specifying two addresses separated by a comma (“,“). An address range matches lines starting from where the first address matches, and continues until the second address matches (inclusively).

If the second address is a regexp, then checking for the ending match will start with the line following the line which matched the first address: a range will always span at least two lines (except of course if the input stream ends).

If the second address is a number less than (or equal to) the line matching the first address, then only the one line is matched.

GNU sed also supports some special two-address forms; all these are GNU extensions:

0,/regexp/A line number of 0 can be used in an address specification like 0,/regexp/ so that sed will try to match regexp in the first input line too. In other words, 0,/regexp/ is similar to 1,/regexp/, except that if addr2 matches the very first line of input the 0,/regexp/ form will consider it to end the range, whereas the 1,/regexp/ form will match the beginning of its range and hence make the range span up to the second occurrence of the regular expression.

Note that this is the only place where the 0 address makes sense; there is no “0th” line, and commands that are given the 0 address in any other way gives an error.

addr1,+NMatches addr1 and the N lines following addr1.
addr1,~NMatches addr1 and the lines following addr1 until the next line whose input line number is a multiple of N.

Appending the ! character to the end of an address specification negates the sense of the match. That is, if the ! character follows an address range, then only lines which do not match the address range will be selected. This also works for singleton addresses, and, perhaps perversely, for the null address.

Overview Of Regular Expression Syntax

To know how to use sed, you should understand regular expressions (“regexp” for short). A regular expression is a pattern that is matched against a subject string from left to right. Most characters are ordinary: they stand for themselves in a pattern, and match the corresponding characters in the subject. As a simple example, the pattern

The quick brown fox

…matches a portion of a subject string that is identical to itself. The power of regular expressions comes from the ability to include alternatives and repetitions in the pattern. These are encoded in the pattern by the use of special characters, which do not stand for themselves but instead are interpreted in some special way. Here is a brief description of regular expression syntax as used in sed:

charA single ordinary character matches itself.
*Matches a sequence of zero or more instances of matches for the preceding regular expression, which must be an ordinary character, a special character preceded by “\“, a “.“, a grouped regexp (see below), or a bracket expression. As a GNU extension, a postfixed regular expression can also be followed by “*“; for example, a** is equivalent to a*. POSIX 1003.1-2001 says that * stands for itself when it appears at the start of a regular expression or subexpression, but many nonGNU implementations do not support this, and portable scripts should instead use “\*” in these contexts.
\+Like *, but matches one or more. It is a GNU extension.
\?Like *, but only matches zero or one. It is a GNU extension.
\{i\}Like *, but matches exactly i sequences (i is a decimal integer; for compatibility, you should keep it between 0 and 255, inclusive).
\{i,j\}Matches between i and j, inclusive, sequences.
\{i,\}Matches more than or equal to i sequences.
\(regexp\)Groups the inner regexp as a whole; this is used to:

  • Apply postfix operators, like \(abcd\)*: this will search for zero or more whole sequences of ‘abcd’, while abcd* would search for ‘abc’ followed by zero or more occurrences of ‘d’. Note that support for \(abcd\)* is required by POSIX 1003.1-2001, but many non-GNU implementations do not support it and hence it is not universally portable.
  • Use back references (see below).
.Matches any character, including a newline.
^Matches the null string at beginning of the pattern space, i.e. what appears after the ^ must appear at the beginning of the pattern space.

In most scripts, pattern space is initialized to the content of each line. So, it is a useful simplification to think of ^#include as matching only lines where ‘#include’ is the first thing on line—if there are spaces before, for example, the match fails. This simplification is valid as long as the original content of pattern space is not modified, for example with an s command.

^ acts as a special character only at the beginning of the regular expression or subexpression (that is, after \( or \|). Portable scripts should avoid ^ at the beginning of a subexpression, though, as POSIX allows implementations that treat ^ as an ordinary character in that context.

$It is the same as ^, but refers to end of pattern space. $ also acts as a special character only at the end of the regular expression or subexpression (that is, before \) or \|), and its use at the end of a subexpression is not portable.
[list]

[^list]

Matches any single character in list: for example, [aeiou] matches all vowels. A list may include sequences like char1char2, which matches any character between char1 and char2. For example, [b-e] matches any of the characters bcd, or e.

A leading ^ reverses the meaning of list, so that it matches any single character not in list. To include ] in the list, make it the first character (after the ^ if needed); to include  in the list, make it the first or last; to include ^ put it after the first character.

The characters $*.[, and \ are normally not special within list. For example, [\*] matches either ‘\’ or ‘*’, because the \ is not special here. However, strings like [.ch.][=a=], and [:space:] are special within list and represent collating symbols, equivalence classes, and character classes, respectively, and [ is therefore special within list when it is followed by .=, or :. Also, when not in POSIXLY_CORRECT mode, special escapes like \n and \t are recognized within list. See Escapes for more information.

regexp1\|regexp2Matches either regexp1 or regexp2. Use parentheses to use complex alternative regular expressions. The matching process tries each alternative in turn, from left to right, and the first one that succeeds is used. This option is a GNU extension.
regexp1regexp2Matches the concatenation of regexp1 and regexp2. Concatenation binds more tightly than \|^, and $, but less tightly than the other regular expression operators.
\digitMatches the digit-th \(\) parenthesized subexpression in the regular expression. This option is called a back reference. Subexpressions are implicitly numbered by counting occurrences of \( left-to-right.
\nMatches the newline character.
\charMatches char, where char is one of $*.[\, or ^. Note that the only C-like backslash sequences that you can portably assume to be interpreted are \n and \\; in particular \t is not portable, and matches a ‘t’ under most implementations of sed, rather than a tab character.

Note that the regular expression matcher is greedy, i.e., matches are attempted from left to right and, if two or more matches are possible starting at the same character, it selects the longest.

For example:

abcdefMatches “abcdef“.
a*bMatches zero or more “a” characters, followed by a single “b“. For example, “b” or “aaaaaaab“.
a\?bMatches “b” or “ab“.
a\+b\+Matches one or more “a” characters followed by one or more “b“s. “ab” is the shortest possible match, but other examples are “aaaaab“, “abbbbbb“, or “aaaaaabbbbbbb“.
.*or .\+Either of these expressions will match all of the characters in a non-empty string, but only .* will match the empty string.
^main.*(.*)This matches a string starting with “main“, followed by an opening and closing parenthesis. The “n“, “(” and “)” need not be adjacent.
^#This matches a string beginning with “#“.
\\$This matches a string ending with a single backslash. The regexp contains two backslashes for escaping.
\$This matches a string consisting of a single dollar sign.
[a-zA-Z0-9]In the C locale, this matches any ASCII letters or digits.
[^ tab]\+(Here tab stands for a single tab character.) This matches a string of one or more characters that does not contain a space or a tab. Usually this means a word.
^\(.*\)\n\1$This matches a string consisting of two equal substrings separated by a newline.
.\{9\}A$This matches nine characters followed by an ‘A’.
^.\{15\}AThis matches the start of a string that contains 16 characters with the last character of being ‘A’.

Often-Used Commands

If you use sed at all, you will probably want to know these commands.

#(No addresses allowed with this command.) The # character begins a comment; the comment continues until the next newline.

If you are concerned about portability, be aware that some implementations of sed (which are not POSIX conformant) may only support a single one-line comment, and then only when the very first character of the script is a #.

Warning: if the first two characters of the sed script are #n, then the -n (no-autoprint) option is forced. If you want to put a comment in the first line of your script and that comment begins with the letter ‘n’ and you do not want this behavior, then be sure to either use a capital ‘N’, or place at least one space before the ‘n’.

q [exit-code]This command only accepts a single address.

Exit sed without processing any more commands or input. Note that the current pattern space is printed if auto-print is not disabled with the -n options. The ability to return an exit code from the sed script is a GNU sed extension.

dDelete the pattern space; immediately start next cycle.
pPrint out the pattern space (to the standard output). This command is usually only used in conjunction with the -n command-line option.
nIf auto-print is not disabled, print the pattern space, then, regardless, replace the pattern space with the next line of input. If there is no more input then sed exits without processing any more commands.
{ commands }A group of commands may be enclosed between { and } characters. This option is particularly useful when you want a group of commands to be triggered by a single address (or address-range) match.

The s Command

The syntax of the s command (which stands for “substitute”) is: ‘s/regexp/replacement/flags’. The / characters may be uniformly replaced by any other single character within any given s command. The / character (or whatever other character is used in its stead) can appear in the regexp or replacement only if it is preceded by a \ character.

The s command is probably the most important in sed and has a lot of different options. Its basic concept is simple: the s command attempts to match the pattern space against the supplied regexp; if the match is successful, then that portion of the pattern space which was matched is replaced with replacement.

The replacement can contain \n (n being a number from 1 to 9, inclusive) references, which refer to the portion of the match that is contained between the nth \( and its matching \). Also, the replacement can contain unescaped & characters which reference the whole matched portion of the pattern space. Finally, as a GNU sed extension, you can include a special sequence made of a backslash and one of the letters LlUu, or E. The meaning is as follows:

\LVire o substituto para minúsculas até que um \ U ou \ E é encontrado
\euVire o próximo caractere para minúsculas
\VOCÊVire a substituição em maiúsculas até que um \ L ou \ E é encontrado
\vocêVire o próximo caractere para maiúsculas
\ EInterromper conversão de caso iniciada por \ L ou \ U

Para incluir uma linha literal \ , & ou nova linha na substituição final, certifique-se de preceder a linha \ , & ou nova linha desejada na substituição com a \ .

O comando s pode ser seguido por zero ou mais dos seguintes sinalizadores:

gAplique a substituição a todas as correspondências na regexp, não apenas na primeira.
númeroSubstitua apenas a correspondência do número th da regexp.

Nota: o padrão POSIX não especifica o que deve acontecer quando você mistura os modificadores g e number , e atualmente não há um significado amplamente aceito nas implementações sed . Para o GNU sed , a interação é definida como: ignorar correspondências antes do número th e, em seguida, corresponder e substituir todas as correspondências a partir do número th.

pSe a substituição foi feita, imprima o novo espaço do padrão.

Nota: quando as opções p e e são especificadas, a ordem relativa das duas produz resultados muito diferentes. Em geral, ep (avaliar e imprimir) é o que você deseja, mas operar de maneira inversa pode ser útil para depuração. Por esse motivo, a versão atual do GNU sed interpreta especialmente a presença de opções p antes e depois de e , imprimindo o espaço do padrão antes e depois da avaliação, enquanto em geral os sinalizadores para o comando s mostram seu efeito apenas uma vez. Esse comportamento, embora documentado, pode ser alterado em versões futuras.

arquivo wSe a substituição foi feita, escreva o resultado no arquivo nomeado . Como uma extensão GNU sed , dois valores especiais de arquivo são suportados: / dev / stderr , que grava o resultado no erro padrão, e / dev / stdout , que grava na saída padrão.
eEste comando permite canalizar a entrada de um comando shell para o espaço do padrão. Se uma substituição foi feita, o comando encontrado no espaço do padrão é executado e o espaço do padrão é substituído por sua saída. Uma nova linha à direita é suprimida; os resultados são indefinidos se o comando a ser executado contiver um caractere nulo. Esta opção é uma extensão sed GNU .
I , iO modificador I para correspondência de expressão regular é uma extensão GNU que faz com que o sed match regexp seja diferenciado por maiúsculas e minúsculas.
M , mO modificador M para correspondência de expressão regular é uma extensão GNU sed que faz com que ^ e $ correspondam respectivamente (além do comportamento normal) à cadeia vazia após uma nova linha e à cadeia vazia antes de uma nova linha. Existem seqüências de caracteres especiais ( \ ` e \ ‘ ) que sempre correspondem ao início ou ao final do buffer. M significa multi-linha.

Comandos menos usados

Embora talvez seja menos usado do que os da seção anterior, alguns scripts sed muito pequenos, porém úteis, podem ser criados com esses comandos.

y / caracteres-fonte caracteres-dest /(Os caracteres / podem ser substituídos uniformemente por qualquer outro caractere único em qualquer comando y ).

Transliterar quaisquer caracteres no espaço do padrão que correspondam a qualquer um dos caracteres de origem com o caractere correspondente nos caracteres de dest .

Instâncias de / (ou qualquer outro caractere usado), \ ou novas linhas podem aparecer nas listas de caracteres de origem ou destino , desde que cada instância seja escapada por um \ . As listas de caracteres de origem e de destino devem conter o mesmo número de caracteres (após o escape).

a \ textComo uma extensão GNU, este comando aceita dois endereços.

Enfileire as linhas de texto que seguem este comando (cada uma, exceto a última terminação com a \ , removidas da saída) para serem exibidas no final do ciclo atual ou quando a próxima linha de entrada for lida.

As seqüências de escape no texto são processadas, portanto, você deve usar \\ no texto para imprimir uma única barra invertida.

Como uma extensão GNU, se entre a uma e a nova linha não é diferente de um whitespace- \ sequência, então o texto desta linha, começando no primeiro carácter não-branco após o um, é tomado como a primeira linha do bloco de texto. (Isso permite uma simplificação no script um add one-line.) Esta extensão também funciona com os i e c comandos.

i \ textComo uma extensão GNU, este comando aceita dois endereços.

Emita imediatamente as linhas de texto que seguem este comando (cada uma, exceto a última terminação com a \ , removidas da saída).

c \ textExclua as linhas correspondentes ao endereço ou intervalo de endereços e imprima as linhas de texto que seguem este comando (cada uma, exceto a última terminação com a \ , removidas da saída) no lugar da última linha (ou no lugar de cada linha, se nenhum endereço foi especificado). Um novo ciclo é iniciado após a conclusão deste comando, pois o espaço do padrão será excluído.
=Como uma extensão GNU, este comando aceita dois endereços.

Imprima o número da linha de entrada atual (com uma nova linha à direita).

eu nPrint the pattern space in an unambiguous form: non-printable characters (and the \ character) are printed in C-style escaped form; long lines are split, with a trailing \ character to indicate the split; the end of each line is marked with a $.

n specifies the desired line-wrap length; a length of 0 (zero) means to never wrap long lines. If omitted, the default as specified on the command line is used. The n parameter is a GNU sed extension.

r file nameAs a GNU extension, this command accepts two addresses.

Queue the contents of file name to be read and inserted into the output stream at the end of the current cycle, or when the next input line is read. Note that if file name cannot be read, it is treated as if it were an empty file, without any error indication.

As a GNU sed extension, the special value /dev/stdin is supported for the file name, which reads the contents of the standard input.

w file nameWrite the pattern space to file name. As a GNU sed extension, two special values of file name are supported: /dev/stderr, which writes the result to the standard error, and /dev/stdout, which writes to the standard output.

The file will be created (or truncated) before the first input line is read; all w commands (including instances of the w flag on successful s commands) which refer to the same file name are output without closing and reopening the file.

DIf pattern space contains no newline, start a normal new cycle as if the d command was issued. Otherwise, delete text in the pattern space up to the first newline, and restart cycle with the resultant pattern space, without reading a new line of input.
NAdd a newline to the pattern space, then append the next line of input to the pattern space. If there is no more input then sed exits without processing any more commands.
PPrint out the portion of the pattern space up to the first newline.
hReplace the contents of the hold space with the contents of the pattern space.
HAppend a newline to the contents of the hold space, and then append the contents of the pattern space to that of the hold space.
gReplace the contents of the pattern space with the contents of the hold space.
GAppend a newline to the contents of the pattern space, and then append the contents of the hold space to that of the pattern space.
xExchange the contents of the hold and pattern spaces.

Commands for sed gurus

In most cases, use of these commands indicates that you are probably better off programming in something like awk or Perl. But occasionally one is committed to sticking with sed, and these commands can enable one to write quite convoluted scripts.

: label[No addresses allowed with this command.] Specify the location of label for branch commands. In all other respects, a no-op (no operation performed).
b labelUnconditionally branch to label. The label may be omitted, in which case the next cycle is started.
t labelBranch to label only if there has been a successful substitution since the last input line was read or conditional branch was taken. The label may be omitted, in which case the next cycle is started.

Commands Specific to GNU sed

These commands are specific to GNU sed, so you must use them with care and only when you are sure that the script will not need to be ported. They allow you to check for GNU sed extensions or to do tasks that are required quite often, yet are unsupported by standard seds.

e [command]This command allows one to pipe input from a shell command into pattern space. Without parameters, the e command executes the command that is found in pattern space and replaces the pattern space with the output; a trailing newline is suppressed.

If a parameter is specified, instead, the e command interprets it as a command and sends its output to the output stream (like r does). The command can run across multiple lines, all but the last ending with a back-slash.

In both cases, the results are undefined if the command to be executed contains a null character.

FPrint out the file name of the current input file (with a trailing newline).
L nThis GNU sed extension fills and joins lines in pattern space to produce output lines of (at most) n characters, like fmt does; if n is omitted, the default as specified on the command line is used. This command is considered a failed experiment and unless there is enough request (which seems unlikely) will be removed in future versions.
Q [exit-code]This command only accepts a single address.

This command is the same as q, but will not print the contents of pattern space. Like q, it provides the ability to return an exit code to the caller.

This command can be useful because the only alternative ways to accomplish this apparently trivial function are to use the -n option (which can unnecessarily complicate your script) or resorting to the following snippet, which wastes time by reading the whole file without any visible effect:
:eat #Quit silently on the last line: $d #Read another line, silently: N #Overwrite pattern space each time to save memory: g b eat.

R file nameQueue a line of file name to be read and inserted into the output stream at the end of the current cycle, or when the next input line is read. Note that if file name cannot be read, or if its end is reached, no line is appended, without any error indication.

As with the r command, the special value /dev/stdin is supported for the file name, which reads a line from the standard input.

T labelBranch to label only if there have been no successful substitutions since the last input line was read or conditional branch was taken. The label may be omitted, in which case the next cycle is started.
v versionThis command does nothing, but makes sed fail if GNU sed extensions are not supported, because other versions of sed do not implement it. Also, you can specify the version of sed that your script requires, such as 4.0.5. The default is 4.0 because that is the first version that implemented this command.

This command enables all GNU extensions even if POSIXLY_CORRECT is set in the environment.

W file nameWrite to the given file name the portion of the pattern space up to the first newline. Everything said under the w command about file handling holds here too.
zThis command empties the content of pattern space. It is usually the same as ‘s/.*//’, but is more efficient and works in the presence of invalid multibyte sequences in the input stream. POSIX mandates that such sequences are not matched by ‘.’, so that there is no portable way to clear sed‘s buffers in the middle of the script in most multibyte locales (including UTF-8 locales).

GNU Extensions for Escapes in Regular Expressions

Until now (in this document, anyway), we have only encountered escapes of the form ‘\^’, for example, which tell sed not to interpret the circumflex (caret) as a special character, but rather to take it literally. For another example, ‘\*’ matches a single asterisk rather than zero or more backslashes.

This section introduces another kind of escape—that is, escapes that are applied to a character or sequence of characters that ordinarily are taken literally, and that sed replaces with a special character. This provides a way of encoding non-printable characters in patterns in a visible manner. There is no restriction on the appearance of non-printing characters in a sed script but when a script is being prepared in the shell or by text editing, it is usually easier to use one of the following escape sequences than the binary character it represents:

\aProduces or matches a bel character, that is an “alert” (ASCII 7).
\fProduces or matches a form feed (ASCII 12).
\nProduces or matches a newline (ASCII 10).
\rProduces or matches a carriage return (ASCII 13).
\tProduces or matches a horizontal tab (ASCII 9).
\vProduces or matches a so called “vertical tab” (ASCII 11).
\cxProduces or matches Control-x, where x is any character. The precise effect of ‘\cx’ is as follows: if x is a lower case letter, it is converted to upper case. Then bit 6 of the character (hex 40) is inverted. Thus ‘\cz’ becomes hex 1A, but ‘\c{’ becomes hex 3B, while ‘\c;’ becomes hex 7B.
\dxxxProduces or matches a character whose decimal ASCII value is xxx.
\oxxxProduces or matches a character whose octal ASCII value is xxx.
\xxxProduces or matches a character whose hexadecimal ASCII value is xx.

\b’ (backspace) was omitted because of the conflict with the existing “word boundary” meaning.

Other escapes match a particular character class and are valid only in regular expressions:

\wMatches any “word” character. A “word” character is any letter or digit or the underscore character.
\WMatches any “non-word” character.
\bMatches a word boundary; that is, it matches if the character to the left is a “word” character and the character to the right is a “non-word” character, or vice-versa.
\BMatches everywhere but on a word boundary; that is it matches if the character to the left and the character to the right are either both “word” characters or both “non-word” characters.
\`Matches only at the start of pattern space. This option is different from ^ in multi-line mode.
\’Matches only at the end of pattern space. This option is different from $ in multi-line mode.

Some Sample Scripts

Here are some sed scripts to guide you in the art of mastering sed.

Sample Script: Centering Lines

This script centers all lines of a file on 80 columns width. To change that width, the number in \{\} must be replaced, and the number of added spaces also must be changed.

Note how the buffer commands are used to separate parts in the regular expressions to be matched—this is a common technique.

#!/usr/bin/sed -f
   
# Put 80 spaces in the buffer
1 {
  x
  s/^$/          /
  s/^.*$/&&&&&&&&/
  x
}
# del leading and trailing spaces
y/tab/ /
s/^ *//
s/ *$//
# add a newline and 80 spaces to end of line
G
# keep first 81 chars (80 + a newline)
s/^\(.\{81\}\).*$/\1/
# \2 matches half of the spaces, which are moved to the beginning
s/^\(.*\)\n\(.*\)\2/\2\1/

Sample Script: Increment A Number

This script is one of a few that demonstrate how to do arithmetic in sed. This script is indeed possible, but must be done manually.

To increment one number you just add 1 to last digit, replacing it by the following digit. There is one exception: when the digit is a nine the previous digits must be also incremented until you don’t have a nine.

This solution is very clever and smart because it uses a single buffer; if you don’t have this limitation, the algorithm used in Numbering Lines is faster. It works by replacing trailing nines with an underscore, then using multiple s commands to increment the last digit, and then again substituting underscores with zeros.

#!/usr/bin/sed -f
/[^0-9]/ d
# replace all leading 9s by _ (any other character except digits, could
# be used)
:d
s/9\(_*\)$/_\1/
td
# incr last digit only.  The first line adds a most-significant
# digit of 1 if we have to add a digit.
#
# The tn commands are not necessary, but make the thing
# faster
s/^\(_*\)$/1\1/; tn
s/8\(_*\)$/9\1/; tn
s/7\(_*\)$/8\1/; tn
s/6\(_*\)$/7\1/; tn
s/5\(_*\)$/6\1/; tn
s/4\(_*\)$/5\1/; tn
s/3\(_*\)$/4\1/; tn
s/2\(_*\)$/3\1/; tn
s/1\(_*\)$/2\1/; tn
s/0\(_*\)$/1\1/; tn
:n
y/_/0/

Sample Script: Rename Files To Lower Case

This script is a pretty strange use of sed. We transform text, and transform it to be shell commands, then just feed them to shell. Don’t worry, even worse hacks are done when using sed. Scripts have even been written converting the output of date into a bc program… So, stranger things have happened.

The main body of this is the sed script, which remaps the name from lower to upper (or vice-versa) and even checks out if the remapped name is the same as the original name. Note how the script is parameterized using shell variables and proper quoting.

#! /bin/sh
# rename files to lower/upper case...
#
# usage:
#    move-to-lower *
#    move-to-upper *
# or
#    move-to-lower -R .
#    move-to-upper -R .
#
help()
{
        cat << eof
Usage: $0 [-n] [-r] [-h] files...
-n      do nothing, only see what would be done
-R      recursive (use find)
-h      this message
files   files to remap to lower case
Examples:
       $0 -n *        (see if everything is ok, then...)
       $0 *
       $0 -R .
eof
}
apply_cmd='sh'
finder='echo "$@" | tr " " "\n"'
files_only=
while :
do
    case "$1" in
        -n) apply_cmd='cat' ;;
        -R) finder='find "$@" -type f';;
        -h) help ; exit 1 ;;
        *) break ;;
    esac
    shift
done
if [ -z "$1" ]; then
        echo Usage: $0 [-h] [-n] [-r] files...
        exit 1
fi
LOWER='abcdefghijklmnopqrstuvwxyz'
UPPER='ABCDEFGHIJKLMNOPQRSTUVWXYZ'
case `basename $0` in
        *upper*) TO=$UPPER; FROM=$LOWER ;;
        *)       FROM=$UPPER; TO=$LOWER ;;
esac
eval $finder | sed -n '
# remove all trailing slashes
s/\/*$//
# add ./ if there is no path, only a file name
/\//! s/^/.\//
# save path+file name
h
# remove path
s/.*\///
# do conversion only on file name
y/'$FROM'/'$TO'/
# now line contains original path+file, while
# hold space contains the new file name
x
# add converted file name to line, which now contains
# path/file-name\nconverted-file-name
G
# check if converted file name is equal to original file name,
# if it is, do not print nothing
/^.*\/\(.*\)\n\1/b
# now, transform path/fromfile\n, into
# mv path/fromfile path/tofile and print it
s/^\(.*\/\)\(.*\)\n\(.*\)$/mv "\1\2" "\1\3"/p
' | $apply_cmd

Sample Script: Print bash Environment

This script strips the definition of the shell functions from the output of the set command in the Bourne-Again shell (bash).

#!/bin/bash
set | sed -n '
:x
# if no occurrence of ‘=()’ print and load next line
/=()/! { p; b; }
/ () $/! { p; b; }
# possible start of functions section
# save the line in case this is a var like FOO="() "
h
# if the next line has a brace, we quit because
# nothing comes after functions
n
/^{/ q
# print the old line
x; p
# work on the new line now
x; bx
'

Sample Script: Reverse Characters Of Lines

This script can be used to reverse the position of characters in lines. The technique moves two characters at a time, hence it is faster than more intuitive implementations.

Note the tx command before the definition of the label. This command is often needed to reset the flag that is tested by the t command.

#!/usr/bin/sed -f
/../! b
# Reverse a line.  Begin embedding the line between two newlines
s/^.*$/\
&\
/
# Move first character at the end.  The regexp matches until
# there are zero or one characters between the markers
tx
:x
s/\(\n.\)\(.*\)\(.\n\)/\3\2\1/
tx
# Remove the newline markers
s/\n//g

Sample Script: Reverse Lines Of Files

This one begins a series of totally useless (yet interesting) scripts emulating various Unix commands. This, in particular, is a tac workalike.

Note that on implementations other than GNU sed this script might easily overflow internal buffers.

#!/usr/bin/sed -nf
# reverse all lines of input, i.e. first line became last, ...
# from the second line, the buffer (which contains all previous lines)
# is *appended* to current line, so, the order will be reversed
1! G
# on the last line we're done -- print everything
$ p
# store everything on the buffer again
h

Sample Script: Numbering Lines

This script replaces ‘cat -n’; in fact it formats its output exactly like GNU cat does.

Of course this is completely useless for two reasons: first, because somebody else did it in C (the cat command), and second, because the following Bourne-shell script could be used for the same purpose and would be much faster:

#! /bin/sh
sed -e "=" $@ | sed -e '
  s/^/      /
  N
  s/^ *\(......\)\n/\1  /
'

It uses sed to print the line number, then groups lines two by two using N. Of course, this script does not teach as much as the one presented below.

The algorithm used for incrementing uses both buffers, so the line is printed as soon as possible and then discarded. The number is split so that changing digits go in a buffer and unchanged ones go in the other; the changed digits are modified in a single step (using a y command). The line number for the next line is then composed and stored in the hold space, to be used in the next iteration.

#!/usr/bin/sed -nf
# Prime the pump on the first line
x
/^$/ s/^.*$/1/
# Add the correct line number before the pattern
G
h
# Format it and print it
s/^/      /
s/^ *\(......\)\n/\1  /p
# Get the line number from hold space; add a zero
# if we're going to add a digit on the next line
g
s/\n.*$//
/^9*$/ s/^/0/
# separate changing/unchanged digits with an x
s/.9*$/x&/
# keep changing digits in hold space
h
s/^.*x//
y/0123456789/1234567890/
x
# keep unchanged digits in pattern space
s/x.*$//
# compose the new number, remove the newline implicitly added by G
G
s/\n//
h

Sample Script: Numbering Non-Blank Lines

Emulating ‘cat -b’ is almost the same as ‘cat -n’: we only have to select which lines are to be numbered and which are not.

The part that is common to this script and the previous one is not commented to show how important it is to comment sed scripts properly…

#!/usr/bin/sed -nf
/^$/ {
  p
  b
}
# Same as cat -n from now
x
/^$/ s/^.*$/1/
G
h
s/^/      /
s/^ *\(......\)\n/\1  /p
x
s/\n.*$//
/^9*$/ s/^/0/
s/.9*$/x&/
h
s/^.*x//
y/0123456789/1234567890/
x
s/x.*$//
G
s/\n//
h

Sample Script: Counting Characters

This script shows another way to do arithmetic with sed. In this case we have to add possibly large numbers, so implementing this by successive increments would not be feasible (and possibly even more complicated to contrive than this script).

The approach is to map numbers to letters, kind of an abacus implemented with sed. ‘a‘s are units, ‘b‘s are tens and so on: we add the number of characters on the current line as units, and then propagate the carry to tens, hundreds, and so on.

As usual, running totals are kept in hold space.

On the last line, we convert the abacus form back to decimal. For the sake of variety, this is done with a loop rather than with some 80 s commands: first we convert units, removing ‘a‘s from the number; then we rotate letters so that tens become ‘a‘s, and so on until no more letters remain.

#!/usr/bin/sed -nf
# Add n+1 a's to hold space (+1 is for the newline)
s/./a/g
H
x
s/\n/a/
# Do the carry.  The t's and b's are not necessary,
# but they do speed up the thing
t a
: a;  s/aaaaaaaaaa/b/g; t b; b done
: b;  s/bbbbbbbbbb/c/g; t c; b done
: c;  s/cccccccccc/d/g; t d; b done
: d;  s/dddddddddd/e/g; t e; b done
: e;  s/eeeeeeeeee/f/g; t f; b done
: f;  s/ffffffffff/g/g; t g; b done
: g;  s/gggggggggg/h/g; t h; b done
: h;  s/hhhhhhhhhh//g
: done
$! {
  h
  b
}
# On the last line, convert back to decimal
: loop
/a/! s/[b-h]*/&0/
s/aaaaaaaaa/9/
s/aaaaaaaa/8/
s/aaaaaaa/7/
s/aaaaaa/6/
s/aaaaa/5/
s/aaaa/4/
s/aaa/3/
s/aa/2/
s/a/1/
: next
y/bcdefgh/abcdefg/
/[a-h]/ b loop
p

Sample Script: Counting Words

This script is almost the same as the previous one, once each of the words on the line is converted to a single ‘a’ (in the previous script each letter was changed to an ‘a’).

It is interesting that real wc programs have optimized loops for ‘wc -c’, so they are much slower at counting words rather than characters. This script’s bottleneck, instead, is arithmetic, and hence the word-counting one is faster (it has to manage smaller numbers).

Again, the common parts are not commented to show the importance of commenting sed scripts.

#!/usr/bin/sed -nf
# Convert words to a's
s/[ tab][ tab]*/ /g
s/^/ /
s/ [^ ][^ ]*/a /g
s/ //g
# Append them to hold space
H
x
s/\n//
# From here on it is the same as in wc -c.
/aaaaaaaaaa/! bx;   s/aaaaaaaaaa/b/g
/bbbbbbbbbb/! bx;   s/bbbbbbbbbb/c/g
/cccccccccc/! bx;   s/cccccccccc/d/g
/dddddddddd/! bx;   s/dddddddddd/e/g
/eeeeeeeeee/! bx;   s/eeeeeeeeee/f/g
/ffffffffff/! bx;   s/ffffffffff/g/g
/gggggggggg/! bx;   s/gggggggggg/h/g
s/hhhhhhhhhh//g
:x
$! { h; b; }
:y
/a/! s/[b-h]*/&0/
s/aaaaaaaaa/9/
s/aaaaaaaa/8/
s/aaaaaaa/7/
s/aaaaaa/6/
s/aaaaa/5/
s/aaaa/4/
s/aaa/3/
s/aa/2/
s/a/1/
y/bcdefgh/abcdefg/
/[a-h]/ by
p

Sample Script: Counting Lines

Sed gives us ‘wc -l’ functionality for free. Here is the code:

#!/usr/bin/sed -nf
$=

Sample Script: Printing The First Lines

This script is probably the simplest useful sed script. It displays the first 10 lines of input; the number of displayed lines is right before the q command.

#!/usr/bin/sed -f
10q

Sample Script: Printing The Last Lines

Printing the last n lines rather than the first is more complex but indeed possible. The n is encoded in the second line, before the bang (“!“) character.

This script is similar to the tac script (above) in that it keeps the final output in the hold space and prints it at the end:

#!/usr/bin/sed -nf
1! {; H; g; }
1,10 !s/[^\n]*\n//
$p
h

Mainly, the scripts keeps a window of 10 lines and slides it by adding a line and deleting the oldest (the substitution command on the second line works like a D command but does not restart the loop).

The “sliding window” technique is a very powerful way to write efficient and complex sed scripts, because commands like P would require a lot of work if implemented manually.

To introduce the technique, which is fully demonstrated in the rest of this chapter and is based on the NP and D commands, here is an implementation of tail using a simple “sliding window.”

This looks complicated but in fact the working concept is the same as the last script: after we have kicked in the appropriate number of lines, however, we stop using the hold space to keep inter-line state, and instead use N and D to slide pattern space by one line:

#!/usr/bin/sed -f
1h
2,10 {; H; g; }
$q
1,9d
N
D

Note how the first, second and fourth line are inactive after the first ten lines of input. After that, all the script does is: exiting on the last line of input, appending the next input line to pattern space, and removing the first line.

Sample Script: Make Duplicate Lines Unique

This script is an example of the art of using the NP and D commands, probably the most difficult to master.

#!/usr/bin/sed -f
h
:b
# On the last line, print and exit
$b
N
/^\(.*\)\n\1$/ {
    # The two lines are identical.  Undo the effect of
    # the n command.
    g
    bb
}
# If the N command had added the last line, print and exit
$b
# The lines are different; print the first and go
# back working on the second.
P
D

As you can see, we maintain a 2-line window using P and D. This technique is often used in advanced sed scripts.

Sample Script: Print Duplicated Lines Of Input

This script prints only duplicated lines, like ‘uniq -d’.

#!/usr/bin/sed -nf
$b
N
/^\(.*\)\n\1$/ {
    # Print the first of the duplicated lines
    s/.*\n//
    p
    # Loop until we get a different line
    :b
    $b
    N
    /^\(.*\)\n\1$/ {
        s/.*\n//
        bb
    }
}
# The last line cannot be followed by duplicates
$b
# Found a different one.  Leave it alone in the pattern space
# and go back to the top, hunting its duplicates
D

Sample Script: Remove All Duplicated Lines

This script prints only unique lines, like ‘uniq -u’.

#!/usr/bin/sed -f
# Search for a duplicate line --- until that, print what you find.
$b
N
/^\(.*\)\n\1$/ ! {
    P
    D
}
:c
# Got two equal lines in pattern space.  At the
# end of the file we exit
$d
# Else, we keep reading lines with N until we
# find a different one
s/.*\n//
N
/^\(.*\)\n\1$/ {
    bc
}
# Remove the last instance of the duplicate line
# and go back to the top
D

Sample Script: Squeezing Blank Lines

Como exemplo final, aqui estão três scripts, de complexidade e velocidade crescentes, que implementam a mesma função que ‘ cat -s ‘, que está espremendo linhas em branco.

A primeira deixa uma linha em branco no começo e no fim, se já houver alguma.

#! / usr / bin / sed -f
# em linhas vazias, junte-se ao próximo
# Observe que há uma estrela no regexp
: x
/ ^ \ n * $ / {
N
bx
}
# agora, aperte todos '\ n', isso também pode ser feito por:
# s / ^ \ (\ n \) * / \ 1 /
s / \ n * / \
/

Este é um pouco mais complexo e remove todas as linhas vazias no início. Deixa uma única linha em branco no final, se houver alguma.

#! / usr / bin / sed -f
# excluir todas as linhas vazias iniciais
1, / ^. / {
/./!d
}
# em uma linha vazia nós a removemos e todos os seguintes
# linhas vazias, mas uma
: x
/./! {
N
s / ^ \ n $ //
tx
}

Isso remove as linhas em branco iniciais e finais. Também é o mais rápido. Note-se que os loops são completamente feitos com n e b , sem depender de sed para reiniciar o script automaticamente no final de uma linha.

#! / usr / bin / sed -nf
# excluir todos os espaços em branco (principais)
/./!d
# chegue aqui: para que haja um não vazio
: x
# imprima
p
# próximo
n
# tem caracteres? imprima novamente, etc ...
/./bx
# não, não tem caracteres: obteve uma linha vazia
: z
# chegar em seguida, se a última linha terminar aqui, então não há rastro
# linhas vazias são gravadas
n
# também está vazio? então ignore e chegue ao próximo ... isso vai
# remove TODAS as linhas vazias
/./!beleza
# todas as linhas vazias foram excluídas / ignoradas, mas temos um não vazio. Como
# o que queremos fazer é apertar, inserir uma linha em branco artificialmente
Eu\
bx

Limitações do GNU sed (e não-limitações)

Para aqueles que desejam escrever scripts sed portáteis , saiba que algumas implementações limitam os comprimentos de linha (para o padrão e os espaços de espera) a não mais que 4000 bytes. A norma POSIX especifica que implementações sed conformes devem suportar pelo menos 8192 bytes de comprimento de linha. O GNU sed não tem limite embutido no comprimento da linha; contanto que ele possa alocar mais memória (virtual), você pode alimentar ou construir linhas pelo tempo que desejar.

No entanto, a recursão é usada para lidar com subpadrões e repetição indefinida. Isso significa que o espaço de pilha disponível pode limitar o tamanho do buffer que pode ser processado por certos padrões.

Expressões regulares estendidas

A única diferença entre expressões regulares básicas e estendidas está no comportamento de alguns caracteres: ‘ ‘,’ + ‘, parênteses e chaves (‘ {} ‘). Embora expressões regulares básicas exijam que elas sejam escapadas se você quiser que elas se comportem como caracteres especiais, ao usar expressões regulares estendidas, você deve escapá-las se desejar que elas correspondam a um caractere literal.

Por exemplo:

abc?Torna-se ‘ abc \? ‘ao usar expressões regulares estendidas. Corresponde à string literal ‘ abc? 
\ +Torna-se ‘ + ‘ ao usar expressões regulares estendidas. Corresponde a um ou mais ‘ c ‘ s.
a \ {3, \}Torna-se ‘ a {3,} ‘ ao usar expressões regulares estendidas. Combina três ou mais ‘ a ‘ s.
\ (abc \) \ {2,3 \}Torna-se ‘ (abc) {2,3} ‘ ao usar expressões regulares estendidas. Ele corresponde tanto ‘ abcabc ‘ ou ‘ abcabcabc ‘.
\ (abc * \) \ 1Torna-se ‘ (abc *) \ 1 ‘ ao usar expressões regulares estendidas. As referências anteriores ainda devem ser ignoradas ao usar expressões regulares estendidas.

Exemplos

sed G myfile.txt> newfile.txt

Espaços duplos o conteúdo do arquivo myfile.txt e grava a saída no arquivo newfile.txt .

sed = meuarquivo.txt | sed 'N; s / \ n / \. / '

Prefixa cada linha do myfile.txt com um número de linha, um ponto e um espaço e exibe a saída.

sed 's / teste / exemplo / g' myfile.txt> newfile.txt

Procura a palavra ” teste ” em myfile.txt e substitui cada ocorrência pela palavra ” exemplo “.

sed -n '$ =' meuarquivo.txt

Conta o número de linhas em myfile.txt e exibe os resultados.

awk – Intérprete para a linguagem de programação de processamento de texto AWK.
ed – Um simples editor de texto.
grep – Filtra o texto que corresponde a uma expressão regular.
substituir – Um utilitário de substituição de cadeia.

21 de novembro de 2019

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