unix команда для извлечения строк с пустыми значениями в определенной позиции в файле фиксированной ширины

Question

У меня есть файл фиксированной ширины без разделителя. Я хотел бы извлечь строки в файле фиксированной ширины, который имеет пустые значения из позиции 550-552

Answer 1

С sed:

sed -nE '/^.{549}[[:blank:]]{3}/p' file

Символами [[:blank:]] являются пробелы или символы табуляции, замените его пробелом, если хотите сопоставить три пробела.

Answer 2

Вы можете использовать egrep (или эквивалентно, grep -E):

#first let's build a test file, using seq to make 549 dummy characters (X), then 3 characters, then some more dummy characters (Y):
laptop:~/tmp$ (for n in `seq 1 549`; do echo -n X;done ;echo -n '   '; echo YYYYYYYYYYYYY ) > file
laptop:~/tmp$ (for n in `seq 1 549`; do echo -n X;done ;echo -n 'zzz'; echo YYYYYYYYYYYYY ) >> file
laptop:~/tmp$ (for n in `seq 1 549`; do echo -n X;done ;echo -n '   '; echo YYYYYYYYYYYYY ) >> file
laptop:~/tmp$ (for n in `seq 1 549`; do echo -n X;done ;echo -n '123'; echo YYYYYYYYYYYYY ) >> file

#then do the actual search
laptop:~/tmp$ egrep '.{549}   ' file
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX   YYYYYYYYYYYYY
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX   YYYYYYYYYYYYY