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What are the escape characters in grep Stack Overflow?
Within double quotes, backslashes that are followed by one of these characters are removed. grep -e”def|zzz” – grep receives def|zzz; because it defaults to basic regular expressions (BRE), | isn’t special 1 and grep tries to match the literal string def|zzz.
What’s the best way to grep words with spaces?
It’s better to use character classes [ [:space:]], or really just match a space. The \\+ may be misleading – in -E mode, it matches a literal +, while without -E the \\+ matches one or more preceding characters. The escaping depends on the mode you are using.
When to use upper or lowercase e in grep?
I suspect grep itself does something special with the literal string \\\\|. The lowercase -e option is used to express multiple search operations. The alternation is implied: Alternatively, you can use the upper -E option for extended regular expression notation:
Why does grep fail to escape the pipe in regex?
The first fails because grep escapes the pipe programmatically, resulting in a literal pipe in the regex. The last attempts fails because \\\\\\| results in a literal backslash then a literal pipe in the regex. According to grep man pages, and especially according to info pages, all examples given for grep include single quotes and not double quotes.
Which is characters need to be quoted in grep not the shell?
The issue that you ran into was with grep not the shell. For which characters need to be quoted in grep, read the manpage’s section on “REGULAR EXPRESSIONS”. and any whitespace. Look under “SHELL GRAMMAR” on the shell’s manpage. grep uses BRE as its regex method.
Which is the escape character for a regexp?
[ is not the only character to escape for regexps. All the RE operators are including . which is common in user names ( r.ot as a regexp matches root for instance). Also, your approach ( getent passwd | grep “^$user:”) is also invalid in that it wouldn’t flag root:0 as invalid for instance.
How to print filenames in grep in shell?
To get each filename printed to the output and THEN have the grep results corresponding to that file printed after, you could wrap the -exec foo {} | grep pipe in a shell: To to make the -H argument of grep work with standard input, if your version of grep supports the –label= option you could do
Are there escape sequences for POSIX extended regular expressions?
The POSIX standard defines no escape sequences for POSIX-Extended regular expressions, except that: Any special character preceded by an escape shall match itself. The effect of any ordinary character being preceded by an escape is undefined.
Can a backslash be escaped in a POSIX regex?
For POSIX extended regexes (ERE), escape these outside character classes (same as PCRE): Escaping any other characters is an error with POSIX ERE. Inside character classes, the backslash is a literal character in POSIX regular expressions. You cannot use it to escape anything.
Can you escape any characters in POSIX ere?
Escaping any other characters is an error with POSIX ERE. Inside character classes, the backslash is a literal character in POSIX regular expressions. You cannot use it to escape anything.