awk: use { or } as the field-separator.
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From: Hongyi Zhao on 21 Feb 2010 01:38 Hi all, I've some text like the following: 80mm]{level.pdf}% Here is how to import EPS art 80mm]{p1.pdf}} 80mm]{p2.pdf}} 80mm]{method1.pdf}} 80mm]{method2.pdf}} 80mm]{method1-calculation}} 80mm]{method2-calculation}} I want to extract the contents among the {} in the above snippet, so I use the following code: $awk -F'\{\}' '{ print $2 }' myfile But I'll meet the following warnings only: awk: warning: escape sequence `\{' treated as plain `{' awk: warning: escape sequence `\}' treated as plain `}' Why? Regards. -- ..: Hongyi Zhao [ hongyi.zhao AT gmail.com ] Free as in Freedom :.
From: Kaz Kylheku on 21 Feb 2010 02:29 On 2010-02-21, Hongyi Zhao <hongyi.zhao(a)gmail.com> wrote: > Hi all, > > I've some text like the following: > > 80mm]{level.pdf}% Here is how to import EPS art > 80mm]{p1.pdf}} > 80mm]{p2.pdf}} > 80mm]{method1.pdf}} > 80mm]{method2.pdf}} > 80mm]{method1-calculation}} > 80mm]{method2-calculation}} > > I want to extract the contents among the {} in the above snippet, so I > use the following code: > > $awk -F'\{\}' '{ print $2 }' myfile You have a double escape here. The token '\{\}' has single quotes, within which the backslash is ordinary; so it denotes a four-character string. Try: echo '\{\}' You're passing the text \{\} to awk, which is lexically analyzing it, recognizing its own kinds of backslash escape. Braces don't in fact have to be escaped in this situation. That is to say, -F{} is a valid shell token representing a word that stands for the string "-F{}". Braces are keywords in the shell only when not combined with other characters. I.e. { and } are keywords, but {} isn't, and of course neither is -F{}. Moreover { and } have their special meaning only in certain contexts (much like other shell keywords). For instance "while" and "for" are keywords, but "echo while for" doesn't fail or do anything weird; when not used as commands, these words just represent text that requires no escaping.
From: pk on 21 Feb 2010 05:35 Hongyi Zhao wrote: > Hi all, > > I've some text like the following: > > 80mm]{level.pdf}% Here is how to import EPS art > 80mm]{p1.pdf}} > 80mm]{p2.pdf}} > 80mm]{method1.pdf}} > 80mm]{method2.pdf}} > 80mm]{method1-calculation}} > 80mm]{method2-calculation}} > > I want to extract the contents among the {} in the above snippet, so I > use the following code: > > $awk -F'\{\}' '{ print $2 }' myfile > > But I'll meet the following warnings only: > > awk: warning: escape sequence `\{' treated as plain `{' > awk: warning: escape sequence `\}' treated as plain `}' You've already got the answer to the "why" question. Moreover, here instead you probably want awk -F '[{}]' ... or awk -F '{|}' ...
From: Stephane CHAZELAS on 21 Feb 2010 11:17 2010-02-21, 10:35(+00), pk: [...] > awk -F '{|}' ... That's incorrect POSIX syntax (leads to unspecified results), you want: awk -F '\{|\}' with a POSIX awk (like with gawk when POSIXLY_CORRECT is on). awk -F '[{}]' is definitely better here. -- St�phane
From: pk on 21 Feb 2010 11:16
Stephane CHAZELAS wrote: > 2010-02-21, 10:35(+00), pk: > [...] >> awk -F '{|}' ... > > That's incorrect POSIX syntax (leads to unspecified results), > you want: > > awk -F '\{|\}' > > with a POSIX awk (like with gawk when POSIXLY_CORRECT is on). That's incorrect as well, and takes you back to the '{|}' case; if you go that route, you need awk -F '\\{|\\}' due to the way awk scans strings. I used just '{|}' because most awk nowadays either do NOT support {} as regex characters (though it's mandated by POSIX), and those that do are smart enough to see that there's nothing to "quantify" there and take the { and } literally. |