1

I am trying to grep with regex that contains pipe character |. However, It doesn't work as expected. The regex does not match the | inclusively as seen in the attach image below.

enter image description here

this is my bash command

cat data | grep "{{flag\|[a-z|A-Z\s]+}}"

the sample data are the following

| 155||NA||{{flag|Central African Republic}}||2.693||NA||0.000||0.000||0.019||0.271||0.281||0.057||2.066
|{{flagicon|Kosovo}} ''[[Kosovo]]'' <ref name="KOS" group=Note>{{Kosovo-note}}</ref>
|{{flagicon|Somaliland}} [[Somaliland|Somaliland region]]
|{{flagicon|Palestine}} ''[[Palestinian Territories]]''{{refn|See the following on statehood criteria:

the expected output is

| 155||NA||{{flag|Central African Republic}}||2.693||NA||0.000||0.000||0.019||0.271||0.281||0.057||2.066

However, having tested it with Regex101.com, the result came out as expected.

  • POSIX (Grep, e.g.), Vim, and Perl are the three major syntaxes for regexes you'll encounter; unfortunately, each of them is quite different, in both ability and syntax. Luckilly, almost all modern software has settled on Perl's syntax. That's the reason any online service will disagree somewhat with grep: JavaScript's regex engine is based on Perl syntax and semantics. – jpaugh Sep 26 '17 at 18:53
4

It appears that grep accepts \| as a separator between alternative search expressions (like | in egrep, where \| matches a literal |).

Apart from that, your expression has other problems:-

  • + is supported in egrep (or grep -E) only.
  • \s is not supported within a [] character group.
  • I don't see the need for | in the character group.

So the following works for grep:-

grep "{{flag|[a-zA-Z ][a-zA-Z ]*}}" <temp

Or (thanks to Glenn Jackman's input):-

grep "{{flag|[a-zA-Z ]\+}}" <temp

In egrep the {} characters have special significance, so they need to be escaped:-

egrep "\{\{flag\|[a-zA-Z ]+\}\}" <temp

Note that I have removed the unnecessary use of cat.

  • You can also do <temp egrep ..., to put temp back at the beginning where it feels natural – jpaugh Sep 26 '17 at 18:39
  • 1
    @jpaugh - Yes, I know, but I usually avoid it because it doesn't work with internal commands. – AFH Sep 26 '17 at 18:43
  • Really? I started using it to break myself of the cat habit; I always think of the file first. Looking at help in bash, I can't see many built-ins which use stdio. It does break read, though; sure enough. – jpaugh Sep 26 '17 at 18:51
  • with basic grep regex, you can change [a-zA-Z ][a-zA-Z ]* to [a-zA-Z ]\+ -- ref: gnu.org/software/gnulib/manual/html_node/… – glenn jackman Sep 26 '17 at 19:26
  • @glennjackman - Thanks very much: I didn't know about that, and I shall certainly use it from now on. I wonder how many of the other ERE specifics can be escaped in BRE... – AFH Sep 26 '17 at 20:14
0

It seems that your request is extract the line contains flag|, using grep may is too complex.

Here I use sed and awk to extrect it, command is

sed -r -n '/flag\|/p' /tmp/temp

awk 'match($0,/flag\|/){print}' /tmp/temp
  • This does not use the same search criteria as the questioner wants: it can yield more lines than are required. If you simplify the search to this extent, then the grep string is equally simplified. – AFH Sep 27 '17 at 11:23

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