I'm parsing the output of a HTTP GET request with sed to retrieve the contents of a given html tag. The result of that request is like this:
"<!DOCTYPE html><html><body><h1>Hello!</h1><p>v1.0.4-b</p></body></html>"
And I want to retrieve the version number inside the p element.
However, sed seems to have a bug in regex parsing.
When I use:
sed 's/.*<p>//'
It correctly replaces the text at the left of the version (i.e., it outputs "v1.0.4-b</p></body></html>"). But, when I try to use regex groups, with
sed 's/.*<p>(.*)<\/p>.*/\1/'
It fails to match and gives an error:
sed: -e expression #1, char 20: invalid reference \1 on `s' command's RHS.
Despite that, when I test the regex on online regex validators it works.
Thank you in advance
You need to use
sed -n 's~.*<p>\([^<]*\)</p>.*~\1~p'
sed -n -E 's~.*<p>([^<]*)</p>.*~\1~p'
See the online demo:
#!/bin/bash
sed -n 's~.*<p>\([^<]*\)</p>.*~\1~p' <<< \
"<!DOCTYPE html><html><body><h1>Hello!</h1><p>v1.0.4-b</p></body></html>"
## => v1.0.4-b
The sed 's/.*<p>(.*)<\p>.*/\1/' command would not work because
You are using a POSIX BRE pattern where the unescaped ( and ) are treated as literal parentheses chars, not a capturing group. In POSIX BRE, you need \(...\) to define a capturing group (this is why you get the invalid reference \1 exception)
If you add -E option to enable POSIX ERE, you can use (...) to define a capturing group
You are not matching /p, you have \p in the pattern.
As there are slashes in the pattern, it is more convenient to choose regex delimiters other than /, I chose ~ here.
Also, I used -n option to suppress default line output and p flag to print only the result of the substitution.
I have the string:
lopy,lopy1,sym,lopy,lopy1,sym"
I want the line to be:
lopy,lopy1,sym,lady,lady1,sym
Which means that all "lad" after the string sym should be replaced. So I ran:
echo "lopy,lopy1,sym,lopy,lopy1,sym" | sed -r 's/(.*sym.*?)lopy/\1lad/g'
I get:
lopy,lopy1,sym,lopy,lad1,sym
Using Perl is not really better:
echo "lopy,lopy1,sym,lopy,lopy1,sym" | perl -pe 's/(.*sym.+?)lopy/${1}lad/g'
yields
lopy,lopy1,sym,lad,lopy1,sym
Not all "lopy" are replaced. What am I doing wrong?
The (.*sym.*?)lopy / (.*sym.+?)lopy patterns are almost the same, .+? matches one or more chars other than line break chars, but as few as possible, and .*? matches zero or more such chars. Mind that sed does not support lazy quantifiers, *? is the same as * in sed. However, the main problem with the regexps you used is that they match sym, then any text after it and then lopy, so when you added g, it just means you want to find more cases of lopy after sym....lopy. And there is only one such occurrence in your string.
You want to replace all lopy after sym, so you can use
perl -pe 's/(?:\G(?!^)|sym).*?\Klopy/lad/g'
See the regex demo. Details:
(?:\G(?!^)|sym) - sym or end of the previous match (\G(?!^))
.*? - any zero or more chars other than line break chars, as few as possible
\K - match reset operator that discards all text matched so far
lopy - a lopy string.
See the online demo:
#!/bin/bash
echo "lopy,lopy1,sym,lopy,lopy1,sym" | perl -pe 's/(?:\G(?!^)|sym).*?\Klopy/lad/g'
# => lopy,lopy1,sym,lad,lad1,sym
If the values are always comma separated, you may replace .*? with ,: (?:\G(?!^)|sym),\Klopy (see this regex demo).
Since OP has mentioned sed so I am adding awk program here. Which could be better choice in comparison to sed. With shown samples, please try following awk program.
echo "lopy,lopy1,sym,lopy,lopy1,sym" |
awk -F',sym,' '
{
first=$1
$1=""
sub(/^[[:space:]]+/,"")
gsub(/lop/,"lad")
$0=first FS $0
}
1
'
Explanation: Adding detailed explanation for above.
echo "lopy,lopy1,sym,lopy,lopy1,sym" | ##Printing values and sending as standard output to awk program as an input.
awk -F',sym,' ' ##Making ,sym, as a field separator here.
{
first=$1 ##Creating first which has $1 of current line in it.
$1="" ##Nullifying $1 here.
sub(/^[[:space:]]+/,"") ##Substituting initial space in current line here.
gsub(/lop/,"lad") ##Globally substituting lop with lad in rest of line.
$0=first FS $0 ##Adding first FS to rest of edited line here.
}
1 ##Printing edited/non-edited line value here.
'
The problem is that the lopy(s) to replace are after sym, with a pattern like sym.*?lopy, so a global replacement looks for yet more of the whole sym+lopy-after-sym (not just for all lopys after that one sym).†
To replace all lopys (after the first sym, followed by another sym) we can capture the substring between syms and in the replacement side run code, in which a regex replaces all lopys
echo "lopy,lopy1,sym,lopy,lopy1,sym" |
perl -pe's{ sym,\K (.+?) (?=sym) }{ $1 =~ s/lop/lad/gr }ex'
To isolate the substring between syms I use \K after the first sym, which drops matches prior to it, and a positive lookahead for the sym after the substring, which doesn't consume anything. The /e modifier makes the replacement side be evaluated as code. In the replacement side's regex we need /r since $1 can't change, and we want the regex to return anyway. See perlretut.
† To match all of abbbb we can't say /ab/g, nor /(a)b/g nor /a(b)/g, because that would look for all repetitions of the whole ab in the string (and find only ab in the beginning).
sed does not support non-greedy wildcards at all. But your Perl script also fails for other reasons; you are saying "match all occurrences of this" but then you specify a regex which can only match once.
A common simple solution is to split the string, and then replace only after the match:
echo "lopy,lopy1,sym,lopy,lopy1,sym" |
perl -pe 'if (#x = /^(.*?sym,)(.*)/) { $x[1] =~ s/lop/lad/g; s/.*/$x[0]$x[1]/ }'
If you want to be fancy, you can use a lookbehind to only replace the lop occurrences after the first sym.
echo "lopy,lopy1,sym,lopy,lopy1,sym" |
perl -pe 's/(?<=sym.{0,200})lop/lad/'
The variable-length lookbehind generates a warning and is only supported in Perl 5.30+ (you can turn it off with no warnings qw(experimental::vlb));.)
Since you have shown an attempted sed command and used sed tag, here is a sed loop based solution:
sed -E -e ':a' -e 's~(sym,.*)lopy~\1lady~g; ta' file
lopy,lopy1,sym,lady,lady1,sym"
Explanation:
:a sets a label a before matching sym,.* pattern
ta jumps pattern matching back to label a after making a substitution
This looping stop when s command has nothing to match i.e. no lopy substring after sym,
I have a text file with the following pattern written to it:
TIME[32.468ms] -(3)-............."TEXT I WANT TO KEEP"
I would like to discard the first part of each line containing
TIME[32.468ms] -(3)-.............
To test the regular expression I've tried the following:
cat myfile.txt | egrep "^TIME\[.*\]\s\s\-\(3\)\-\.+"
This identifies correctly the lines I want. Now, to delete the pattern I've tried:
cat myfile.txt | sed s/"^TIME\[.*\]\s\s\-\(3\)\-\.+"//
but it just seems to be doing the cat, since it shows the content of the complete file and no substitution happens.
What am I doing wrong?
OS: CentOS 7
With your shown samples, please try following grep command. Written and tested with GNU grep.
grep -oP '^TIME\[\d+\.\d+ms\]\s+-\(\d+\)-\.+\K.*' Input_file
Explanation: Adding detailed explanation for above code.
^TIME\[ ##Matching string TIME from starting of value here.
\d+\.\d+ms\] ##Matching digits(1 or more occurrences) followed by dot digits(1 or more occurrences) followed by ms ] here.
\s+-\(\d+\)-\.+ ##Matching spaces91 or more occurrences) followed by - digits(1 or more occurrences) - and 1 or more dots.
\K ##Using \K option of GNU grep to make sure previous match is found in line but don't consider it in printing, print next matched regex part only.
.* ##to match till end of the value.
2nd solution: Adding awk program here.
awk 'match($0,/^TIME\[[0-9]+\.[0-9]+ms\][[:space:]]+-\([0-9]+\)-\.+/){print substr($0,RSTART+RLENGTH)}' Input_file
Explanation: using match function of awk, to match regex ^TIME\[[0-9]+\.[0-9]+ms\][[:space:]]+-\([0-9]+\)-\.+ which will catch text which we actually want to remove from lines. Then printing rest of the text apart from matched one which is actually required by OP.
This awk using its sub() function:
awk 'sub(/^TIME[[][^]]*].*\.+/,"")' file
"TEXT I WANT TO KEEP"
If there is replacement, sub() returns true.
$ cut -d'"' -f2 file
TEXT I WANT TO KEEP
You may use:
s='TIME[32.468ms] -(3)-............."TEXT I WANT TO KEEP"'
sed -E 's/^TIME\[[^]]*].*\.+//'
"TEXT I WANT TO KEEP"
The \s regex extension may not be supported by your sed.
In BRE syntax (which is what sed speaks out of the box) you do not backslash round parentheses - doing that turns them into regex metacharacters which do not match themselves, somewhat unintuitively. Also, + is just a regular character in BRE, not a repetition operator (though you can turn it into one by similarly backslashing it: \+).
You can try adding an -E option to switch from BRE syntax to the perhaps more familiar ERE syntax, but that still won't enable Perl regex extensions, which are not part of ERE syntax, either.
sed 's/^TIME\[[^][]*\][[:space:]][[:space:]]-(3)-\.*//' myfile.txt
should work on any reasonably POSIX sed. (Notice also how the minus character does not need to be backslash-escaped, though doing so is harmless per se. Furthermore, I tightened up the regex for the square brackets, to prevent the "match anything" regex you had .* from "escaping" past the closing square bracket. In some more detail, [^][] is a negated character class which matches any character which isn't (a newline or) ] or [; they have to be specified exactly in this order to avoid ambiguity in the character class definition. Finally, notice also how the entire sed script should normally be quoted in single quotes, unless you have specific reasons to use different quoting.)
If you have sed -E or sed -r you can use + instead of * but then this complicates the overall regex, so I won't suggest that here.
A simpler one for sed:
sed 's/^[^"]*//' myfile.txt
If the "text you want to keep" always surrounded by the quote like this and only them having the quote in the line starting with "TIME...", then:
sed -n '/^TIME/p' file | awk -F'"' '{print $2}'
should get the line starting with "TIME..." and print the text within the quotes.
Thanks all, for your help.
By the end, I've found a way to make it work:
echo 'TIME[32.468ms] -(3)-.............TEXT I WANT TO KEEP' | grep TIME | sed -r 's/^TIME\[[0-9]+\.[0-9]+ms\]\s\s-\(3\)-\.+//'
More generally,
grep TIME myfile.txt | sed -r ‘s/^TIME\[[0-9]+\.[0-9]+ms\]\s\s-\(3\)-\.+//’
Cheers,
Pedro
Assume the following is in file.txt:
---------
foo bar
more foo bar
---------
when I execute grep -P '(?<=-$)(?s:.)*(?=^-)' file.txt, I expect only the middle two lines to be matched, but this expression matches nothing. What's wrong?
I also tried grep -P '(?s)(?<=-$).*(?=^-)' file.txt but same result.
Your pattern dos not work because
The P option alone only makes grep match using the PCRE regex engine
Since you have no other options, grep outputs whole matched lines, you need to add o option to output the matched text(s) and z to slurp the file into a single text
Your regex has ^ and $ anchors that match start/end of the string, not lines, by default. You need a m flag together with s flag (it makes . match any char including line break chars).
So, you may use your regex with m and -oz:
grep -Poz '(?ms)(?<=-$).*(?=^-)' file.txt
Or,
grep -Poz '(?s)-\R\K.*(?=\R-)' file.txt
where \R matces any line break sequence and \K omits the text matched so far from the overall memory buffer.
See the regex demo.
I have the following lines in an apache access log
/sms/receiveHLRLookup?Ported=No&Status=Success&MSISDN=647930229655&blah
/sms/receiveHLRLookup?Ported=No&Status=Success&MSISDN=647930229656&blah
/sms/receiveHLRLookup?Ported=No&Status=Success&MSISDN=647930229657&blah
/sms/receiveHLRLookup?Ported=No&Status=Success&MSISDN=647930229658&blah
and i want to extract the MSISDN value only, so expected output would be
647930229655
647930229656
647930229657
647930229658
I'm using the following sed command but i can't get it to stop capturing at &
sed 's/.*MSISDN=\(.*\)/\1/'
sed solution:
sed -E 's/.*&MSISDN=([^&]+).*/\1/' file
& - is key/value pair separator in URL syntax, so you should rely on it
([^&]+) - 1st captured group containing any character sequence except &
\1 - backreference to the 1st captured group
The output:
647930229655
647930229656
647930229657
647930229658
-o : means print only matching string not the whole line.
-P: To enable pcre regex.
\K: means ignore everything on the left. But should be part of actual input string.
\d: means digit, + means one or more digit.
grep -oP 'MSISDN=\K\d+' input
647930229655
647930229656
647930229657
647930229658
Following simple sed may help you on same.
sed 's/.*MSISDN=//;s/&.*//' Input_file
Explanation:
s/.*MSISDN=//: s means substitute .*MSISDN= string with // NULL in current line.
; semi colon tells sed that there is 1 more statement to be executed.
s/&.*//g': s/&.*// means substitute &.* from & to everything with NULL.
$ grep -oP '(?<=&MSISDN=)\d+' file
647930229655
647930229656
647930229657
647930229658
-o option is meant to show only matched output
-P option is meant to enable PCRE (Perl Compatible Regex)
(?<=regex) this is to enforce positive look behind assertion. You can read more about them over here. Lookarounds dont consume any characters while matching unlike normal regex. Hence the only matched output you get it \d+ which is 1 or more digits.
or using sed:
$ sed -r 's/^.*MSISDN=([0-9]+).*$/\1/' file
647930229655
647930229656
647930229657
647930229658
you can also pipe cut to cut
cut -d '&' -f3 Input_file |cut -d '=' -f2