grep 和 perl 正则表达式之间的区别？

Question

I have a problem with what I think is a difference in grep's regex and perl's regex. Consider the following little test:

$ cat testfile.txt 
A line of text
SOME_RULE = $(BIN)
Another line of text

$ grep "SOME_RULE\s*=\s*\$(BIN)" testfile.txt 
SOME_RULE = $(BIN)

$ perl -p -e "s/SOME_RULE\s*=\s*\$(BIN)/Hello/g" testfile.txt
A line of text
SOME_RULE = $(BIN)
Another line of text

As you can see, using the regex "SOME_RULE\\s*=\\s*$(BIN)", grep could find the match, but perl was unable to update the file using the same expression. How should I solve this problem?

Answer 1

Perl wants the '(' and ')' to be escaped. Also, the shell eats the '\\' on the '$', so you need:

$ perl -p -e "s/SOME_RULE\s*=\s*\\$\(BIN\)/Hello/g" testfile.txt

(or use single quotes--which is highly advisable in any case.)

Answer 2

You need to escape ( and ) (Capturing group).

perl -p -e 's/SOME_RULE\s*=\s*\$\(BIN\)/Hello/g' testfile.txt

Actually you need it in Extended Regular Expression( ERE ):

grep -E "SOME_RULE\s*=\s*\$\(BIN\)" testfile.txt

Answer 3

perl -ne '(/SOME_RULE\s*?=\s*?\$\(BIN\)/) && print' testfile.txt

如果要修改使用

perl -pe 's/SOME_RULE\s*?=\s*?\$\(BIN\)/Hello/' testfile.txt

Answer 4

Perl's regex syntax is different to the POSIX regexes used by grep. In this case, you're falling foul of parentheses being metacharacters in Perl's regexes - they denote a capturing group.

You should have more success by altering the Perl regex:

s/SOME_RULE\s*=\s*\$\(BIN\)/Hello/g

which will then match the literal parentheses in the source text.