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On Mon, Nov 07, 2005 at 03:42:05AM -0200, Rafael Barreto wrote: |
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> Other thing... Why was necessary to ^CLOCK= before |
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> s/^\(CLOCK=".*"\).*$/\1/p? And which the necessity of the ( ) between the |
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> regular expression? |
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as I just posted in another post, the /^CLOCK/ should not be strictly |
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necessary. |
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See below for an explanation of the () |
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> |
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> |
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> 2005/11/7, Rafael Barreto <rafaelmbarreto@×××××.com>: |
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> > |
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> > For that I understood, this command will return the line of CLOCK= in |
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> > /etc/conf.f/clock without any comments. Is this right? Well, what I really |
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> > want is replace just CLOCK="fool1" by CLOCK="fool2" keeping the comments in |
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> > line. |
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> > |
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Do you know what fool2 would be? If so: |
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s/^\(CLOCK="\)[^["]]*\(".*\)$/\1fool2\2/p |
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should do what you want. (I think sed greedy matches by default? Hum, |
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I honestly don't remember, better safe than sorry.) |
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See below for the use of the \( .. \) and \1 \2 variables. |
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The [^["]] specifies a class of characters to match, in this case, it |
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means anything except for the quotation mark. (The caret ^ negates the |
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class ["] which means only the quotation mark.) So what this sed |
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expression is really saying is that we want to keep the beginning of |
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the line up to the first quotation mark the same, and keep the end of |
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the line starting from the second quotation mark the same, and change |
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everything in between to 'fool2'. |
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> > By the way, \1 do really what? If i put \0 the result is the entire line. |
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> > So, could you explain me this a little more? Thanks... |
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> > |
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\0 is the entire matching expression/line. |
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\n is tokenizing. By using parentheses in the regexp, you can reuse |
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the texts in the parentheses in the substitution. |
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For example, consider the expression |
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s/\(.at\).*\(.ox\)/\2 not \1/p |
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If we send it |
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The bat scared the fox. |
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it would print |
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fox not bat |
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because \2 gets replaced by the second matching token, which in this |
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case, is fox, because it matches ".ox". Similarly for bat and the |
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first token. |
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If we send the same expression |
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The cat died in the box. |
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it would print |
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box not cat |
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I can't explain the concept very well, and I hope the examples are |
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good enough. |
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Seriously, one of the best way to learn sed is to read the manual from |
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`info sed' |
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W |
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-- |
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Here lies Lester Moore |
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Four slugs from a .44 |
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No Les No more. |
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Sortir en Pantoufles: up 4 days, 8:14 |
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-- |
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