I'm trying to write a grep command to find lines like the below in a large text file:
<div class="node_thumbnail" data-type="file" name="GOPR0036.MP4_frame000001.jpg" data="813334c25191468c9f1c57afc99fde60" aid="133948" rel="/Files/ToolTipView?fileId=813334c25191468c9f1c57afc99fde60&pageNo=1&NoCache=101016083044" rev="topMiddle">
but the + symbol seems to be causing problems in the below commands:
grep 'data=[a-z,0-9,\"]' file
Lots of hits
grep 'data=[a-z,0-9,\"]+' file
No hits
If you want + to mean "one or more of the preceding atom", then you have to do one of:
Use -E (Extended Regular Expressions) (or -P, PCRE):
grep -E 'data=[a-z,0-9,\"]+' file
Escape + so that is treated specially in the Basic Regular Expressions used by default in grep:
grep 'data=[a-z,0-9,"]\+' file
data=, you could just run grep -P 'data=".+?" or, to get only the string and nothing else: grep -oP '\bdata="\K[^"]+'.
-o option as well. I edited my previous comment. And you're welcome :)
sed -n 's/.*data="\([^"][^"]*\)".*/\1/p' file, which is fully POSIX compliant. (And sed -nE 's/.*data="([^"]+)".*/\1/p' file will be POSIX compliant for the next edition of POSIX.)
Points:
+ is an ERE (Extended Regular Expression) token, which indicates one or more of the preceding token, can be used if -E option of grep is used or with escaped (\+) in case of BRE (Basic Regex) i.e. only regular grep
The character class [a-z,0-9,\"] would match any of the characters between [a-z], [0-9], , or ". This may not be what you want
Normally grep outputs whole line, if you want to output only the matched portion, use -o option of grep
Based on your example, you can do:
grep -E '\bdata=[a-z0-9"]+\b' file
-E enables ERE\b matches string edges, zero widthdata= matches data= literally[a-z0-9"] matches any character of [a-z], [0-9], and ". + matches the previous token one or more timesYour current pattern even you make it correct, without \b this would match false positives like foo fdata=2322ab, data=12AB and so on.
Example:
% grep -oE '\bdata=[a-z0-9"]+\b' <<<'<div class="node_thumbnail" data-type="file" name="GOPR0036.MP4_frame000001.jpg" data="813334c25191468c9f1c57afc99fde60" aid="133948" rel="/Files/ToolTipView?fileId=813334c25191468c9f1c57afc99fde60&pageNo=1&NoCache=101016083044" rev="topMiddle"'
data="813334c25191468c9f1c57afc99fde60
Another option is to use egrep:
egrep 'data=[a-z,0-9,\"]+' file
egrep is bundled with grep, it is just a wrapper for grep:
#!/bin/sh
exec grep -E "$@"
this is good for interactive use. However in scripts I would use grep -E.
egrep. It has been deprecated in favor of grep -E for many years now. As the POSIX specs state, it is still supported and likely to be so for a while but the current POSIX (and GNU) grep has been designed to replace the older egrep and fgrep variants so it is better to use grep -E and grep -f instead.
LC_ALL="C" grep ...instead ofgrep ..., so that [a-z] means always ascii letters a to z (ie, all lowercase ascii letters) instead of funny alternatives (ex: every letters except "Z", in some locales...)[a-z,0-9,\"]contains 2 occurence of ",", which is not necessary. you can have the same effect with[a-z,0-9\"]