awk and getline
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From: Ed Morton on 19 May 2010 17:08 On 5/19/2010 3:18 PM, mrk wrote: > Janis Papanagnou napisal w dniu 2010-05-19 20:50: >> mrk wrote: >>> Jon LaBadie napisal w dniu 2010-05-19 16:34: >>>> >>>> >>>> desc != 0 { print $0 } >>>> desc != 0 { print } >>>> desc != 0 >>>> desc >>>> >>>> As awk statements, each of the above is equivalent due to awk's >>>> defaults. >>> >>> I'm afraid that it is to clever for me. >>> I don't see connection between this variable, also why variable is >>> placed beyond brackets {}. I've wrote variable inside {}. >>> Now I'm perform command awk with several different settings for practice >>> like: >>> >>> awk '/error/a' file.txt - shows me all lines (no matter for awk that >>> pattern /error/ is set) >> >> (Why would you want to write that?) >> >>> >>> awk 'a' file.txt - shows nothing >> >> Variable a is 0, which equals 'false', thus no lines are printed. >> >>> >>> awk '1' file.txt - shows me all lines >> >> Constant 1 is equivalent to 'true', thus all lines are printed. >> >>> >>> Could you describe me how it works with examples please. >> >> You gave the examples already. But mostly just your second example makes >> sense in some appropriate context where you have some other awk actions >> besides the check against 'a'. Instead of '1' you would (more legible) >> write '{print $0}'. Abstract examples are >> >> awk ' >> condition { do_something_with_a_eg_set_or_unset_a } >> a ## condition a equals "print if set" >> ' >> >> awk ' >> condition { manupulate_the_line } >> 1 ## condition 1 equals "print the line" >> ' >> >> >> Janis >> >>> >>> >>> >>> > I think that I understand a little. > The key-word is "condition". Prewiously I couldn't tie between condition > and {program/commands}. > But it's become clear for me. > > Everything after "'" is condition and after "{" is do if condition true. > For awk every true condition is 1 and false is 0. Now I understand (I > think) how it works. It's very simple: awk scripts like: awk 'script' file are condition { action } statements. It's not that every true condition is "1", but rather every "1" is a true condition. "27" is also a true condition, but not every true condition is "27". Ed. |