What the equivalent of "grep | cut" using sed or awk?

Question

Say I had a config file /etc/emails.conf

email1 = user@dinkum.dorg 
email2 = user@winkum.worg
email3 = user@stinkum.storg

and I wanted to get email2

I could do a:

grep email2 /etc/emails.conf | cut -d'=' -f2

to get the email2, but how do I do it "cooler" with one sed or awk command and remove the whitespace that the cut command would leave?

You can remove the first cat: grep email2 /etc/emails.conf | ... — Carlos Campderrós, May 04 '15 at 15:59
@CarlosCampderrós dang, I had thought I tried that but it failed for some completely unknown hidden reason (because obviously it should have worked). I just put the file name at the end of the cut wrongly and that's why it didn't work. I revised the question, I don't think it invalidates the answers. — Peter Turner, May 04 '15 at 16:20
I really don't understand your question: you already have the string that you're searching for: result="email2" -- what are you really trying to do? — glenn jackman, May 05 '15 at 01:25

score 5 · Accepted Answer · edited Nov 25 '16 at 21:07

5

How about using awk?

awk -F = '/email2/ { print $2}' /etc/emails.conf

-F = Fields are separated by '='
'/email2/ { print $2}' On lines that match "email2", print the second field

edited Nov 25 '16 at 21:07

wjandrea

658

answered May 04 '15 at 15:58

Carlos Campderrós

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can it trim the leading space too? – Peter Turner May 04 '15 at 16:23
1

@PeterTurner, my version of awk permits -F ' *= *', which is a wildcarded expression that groups spaces either side of = as part of the separator. – Chris Davies May 04 '15 at 19:32

Stéphane Chazelas · Answer 2 · 2015-05-04T16:09:25.443

4

The exact equivalent would be something like:

sed -n '/email2/{s/^[^=]*=\([^=]*\).*/\1/;p;}' < file

But you'd probably want instead:

sed -n 's/^[^=]*email2[^=]*=[[:blank:]]*//p' < file

(that is match email2 only on the part before the first = and return everything on the right of the first = (skipping leading blanks), not only the part up to the second = if any).

edited May 04 '15 at 16:09

answered May 04 '15 at 16:00

Stéphane Chazelas

544,893

Is space required between { s? – cuonglm May 04 '15 at 16:02
@cuonglm, no. AFAICT, ;} above is not POSIX but I don't know of any modern sed implementation where that fails. – Stéphane Chazelas May 04 '15 at 16:08
Yes, that's exactly I have stucked when working with this. After re-reading POSIX sed documentation, I see ;} is an accepted extension, but it's not required. It's strange that GNU sed with --posix option still allow {command} form. Do you think it's a bug? – cuonglm May 04 '15 at 16:12
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@cuonglm {command} is not required to report an error by POSIX. It's just that a POSIX script must not use it as the behaviour is not specified there. Where GNU sed is not conformant even with --posix is that it doesn't accept ; in label names. – Stéphane Chazelas May 04 '15 at 16:23
is it preferable to us "<" vs just using the file as the argument (I'm putting this into a bash script)? – Peter Turner May 04 '15 at 16:31
1

@PeterTurner, see When should I use input redirection?. – Stéphane Chazelas May 05 '15 at 08:45
I can't find where ;} is mentioned in the Sed POSIX specs as an accepted extension. It seems to be required by The <right-brace> shall be preceded by a <newline> or <semicolon>. @cuonglm or Stephane, could you clarify? – Wildcard Nov 02 '16 at 04:10
@Wildcard Yes, ;} is not POSIX, that what Stephane said in his comment above. But I remember it will be in next POSIX version, there's an issue in austin bug group. – cuonglm Nov 02 '16 at 04:22
@cuonglm, no, I mean I don't see it as just an extension. "The right brace shall be preceded by a newline or semicolon...." So if you precede it with a semicolon in your Sed script, haven't you followed the explicit instructions of POSIX? – Wildcard Nov 02 '16 at 04:52
@cuonglm, huh, I still don't see it in the specs. But if it will be changed in the next POSIX edition I suppose it's not critical. :) – Wildcard Nov 02 '16 at 06:19
@Wildcard: The austinbug group link http://austingroupbugs.net/view.php?id=961 – cuonglm Nov 02 '16 at 06:26
@Wildcard Ops, look like the spec was changed follow that issue. – cuonglm Nov 02 '16 at 06:30
Let us continue this discussion in chat. – Wildcard Nov 02 '16 at 07:08
Unfortunately, this answer does little to explain why the command works. I've posted an alternative sed answer with that explanation. – cbarrick Dec 19 '18 at 07:58

JJoao · Answer 3 · 2015-05-04T17:41:49.900

2

perl -nlE 's/email2\s*=\s*// and say'    file

Where:

perl -nl is a for each line do...
s/email2 = // removes the searched email id and if you could do it ...
say prints the current input input line
\s* zero or more spaces (equivalent to [ \t\n]*)

edited May 04 '15 at 17:41

answered May 04 '15 at 16:48

JJoao

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I'll give you a +1 for golfing, but where I'm running this (some sort of stripped down Cisco appliance), I'm not sure I'm going to have perl, especially the version of perl that has say. – Peter Turner May 04 '15 at 17:51
perl 5.10 appeared 7 year ago but sometimes we don't have it... perl -nle 's/email2\s*=\s*// and print' – JJoao May 04 '15 at 17:59

score 2 · Answer 4 · answered Dec 19 '18 at 07:56

To get something like grep | cut you can use sed -n s/A/B/p.

By default, sed prints every line after all commands are processed. You can silence all output that you don't explicitly print from a command with sed -n.

The s command takes the form s/$FIND/$REPLACE/$FLAGS. Specifically, the p flag prints the line whenever a replacement is made.

With these combined, you can easily match and cut:

sed -nE "s/email2 = (.+)/\1/p" < /etc/emails.conf

In fact, this is strictly more powerful than grep | cut because you can use an arbitrary replacement pattern.

(The -E option enables modern regex, which allows you to reference capture groups in the replacement pattern. For a simple cut, you can get away without it by using more clever patterns.)

score 0 · Answer 5 · answered May 05 '15 at 16:20

There is no need to set the field separator to any special value such as "=". By default, AWK uses contiguous spaces and tabs as field separators, which are skipped, so it will interpret each line of your file as having three fields, without any leading space on field three

awk '/^email2/ { print $3 }'

produces

user@winkum.worg

The above would also match any lines starting with email2, such as email20, for exact match you can use

awk '$1 == "email2" { print $3 }'

What the equivalent of "grep | cut" using sed or awk?

5 Answers5