Rewind Function (The GNU Awk User’s Guide)
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10.3.2 Rereading the Current File
Another request for a new built-in function was for a function that would make it possible to reread the current file. The requesting user didn’t want to have to use getline
(see section Explicit Input with getline) inside a loop.
However, as long as you are not in the END
rule, it is quite easy to arrange to immediately close the current input file and then start over with it from the top. For lack of a better name, we’ll call the function rewind()
:
# rewind.awk --- rewind the current file and start over function rewind( i) { # shift remaining arguments up for (i = ARGC; i > ARGIND; i--) ARGV[i] = ARGV[i-1] # make sure gawk knows to keep going ARGC++ # make current file next to get done ARGV[ARGIND+1] = FILENAME # do it nextfile }
The rewind()
function relies on the ARGIND
variable (see section Built-in Variables That Convey Information), which is specific to gawk
. It also relies on the nextfile
keyword (see section The nextfile Statement). Because of this, you should not call it from an ENDFILE
rule. (This isn’t necessary anyway, because gawk
goes to the next file as soon as an ENDFILE
rule finishes!)
You need to be careful calling rewind()
. You can end up causing infinite recursion if you don’t pay attention. Here is an example use:
$ cat data -| a -| b -| c -| d -| e $ cat test.awk -| FNR == 3 && ! rewound { -| rewound = 1 -| rewind() -| } -| -| { print FILENAME, FNR, $0 } $ gawk -f rewind.awk -f test.awk data -| data 1 a -| data 2 b -| data 1 a -| data 2 b -| data 3 c
-| data 4 d -| data 5 e
Next: File Checking, Previous: Filetrans Function, Up: Data File Management [Contents][Index]