regular expression

Regular expressions grep

Use the basic regular expression to query the blank line in the file and the first line is “#” Outside the line ( It is usually used to view the effective configuration file ), perform “grep -v ‘^ $ ’ test.txt l grep -v ‘^#’ That is to say . You need to use the pipeline command to search twice . If you use extended regular expressions , It can be simplified as egrep -v ’ ^$’ test.txt

cut

cut Only good at dealing with text separated by a single character

sort

uniq

tr

tr -s ‘\n’ When multiple carriage returns are encountered, only one carriage return is reserved , Equivalent to removing empty lines

sed Tools

If you delete duplicate blank lines , That is to say, there is only one continuous blank line ,cat -s test .txt

expect

awk