CODEWITHSUNDEEP
perlregex-lookaroundsifconfigpcregrep
Marek Stepanek
Marek Stepanek

Reputation: 139

translate pcregrep into Perl one-liner

I need to find all active network interfaces on new macOS. That means the following one-liner with pcregrep will not work:

ifconfig | pcregrep -M -o '^[^\t:]+(?=:([^\n]|\n\t)*status: active)'

because pcregrep is no default install on macOS.

I tried to translate it into egrep to no avail, because a positive lookahead is not possible, right?

So I tried with a one-liner in perl. But the following command is not working, because the switch -pe is not gobbling up all lines together. I tried with -p0e too.

ifconfig | perl -pe 'while (<>) {if (/^[^\t:]+(?=:([^\n]|\n\t)*status: active)/){print "$1";};}'

If I search with a positive lookahead the same line, it is working; for example:

ifconfig | perl -pe 'while (<>) {if (/^([^\t:]+)(?=:([^\n]|\n\t)*mtu 1380)/){print "$1";};}'
utun0

A typical output of ifconfig:

en10: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
    options=6467<RXCSUM,TXCSUM,VLAN_MTU,TSO4,TSO6,CHANNEL_IO,PARTIAL_CSUM,ZEROINVERT_CSUM>
    ether 00:e0:4c:68:01:20
    inet6 fe80::1470:31b9:a01c:6f5e%en10 prefixlen 64 secured scopeid 0xd
    inet 192.168.178.39 netmask 0xffffff00 broadcast 192.168.178.255
    inet6 2003:ee:4f1a:ce00:864:f90c:9a11:6ad9 prefixlen 64 autoconf secured
    inet6 2003:ee:4f1a:ce00:d89a:7e34:6dd4:1370 prefixlen 64 autoconf temporary
    nd6 options=201<PERFORMNUD,DAD>
    media: autoselect (1000baseT <full-duplex>)
    status: active

The expected result would be:

en10

I am on macOS Monterey, zsh and perl 5.34

Thank you for your help

marek

Upvotes: 2

Views: 134

Answers (3)

zdim
zdim

Reputation: 66873

Since output of ifconfig normally† has a multiline block of text for each interface, all separated by blank lines, it is convenient to read it in paragraphs (-00). Then the rest simplifies a lot

ifconfig -a | perl -00 -nE'say $1 if /^(.+?)\s*:.*?status:\s+active/s'

We still need the /s modifier, making . match a newline as well, as each paragraph itself is a multiline string and the pattern needs to match across multiple lines.

† Except that it doesn't on the MacOS used for this question -- there are no blank lines separating blocks for interfaces. Then there is no point in seeking paragraphs (breaking on newline which isn't) and this answer doesn't work for that system.

Here is then a classic line-by-line approach that does -- set the interface name at the first line for that interface's output (no spaces at line beginning), then test for active status

perl -wnE'$ifn=$1, next if /^(\S[^:]+?)\s*:/; say $ifn if /status:\s+active/' file

This allows spaces inside an interface name, what is very unlikely (and perhaps not even allowed). For a more restrictive pattern, which doesn't allow spaces in the name, use /^(\S+?)\s*:/ (or the more efficient /^([^:\s]+)/). The \s* and the preceding ? are there only to make it not capture the trailing spaces (right before :), if any were possible.

This works in the case when there are empty lines between interface blocks as well.

Upvotes: 3

Wiktor Stribiżew
Wiktor Stribiżew

Reputation: 626690

You can use

perl -0777 -nE 'say "$&" while /^[^\n\r\t:]+(?=:(?:.*\R\t)*status:\h+active)/gm'

See the regex test.

Here, -0777 slurps the file so that a regex could match multiline text spans (the M equivalent that exposes the newlines to the pattern in pcregrep), say "$&" prints all matched substrings (the o equivalent, also see g flag).

I edited the [^\t:]+ to match any one or more chars other than tabs, colons and also CR/LF chars. Also, I replaced ([^\n]|\n\t)* into a more efficient (?:.*\R\t)* that matches zero or more occurrences of any zero or more chars other than line break chars till the end of a line (.*), then a line break sequence (\R), and then a tab char (\t).

Also, note the m flag to make ^ anchor also match any line start position.

Upvotes: 2

Dave Mitchell
Dave Mitchell

Reputation: 2403

perl's -n and -p command-line switches add an implicit while (<>) {...} block around the -e code, and in addition -p prints the line at the end of each iteration. So you need to change the -p to -n and only print out the lines which match; and remove the extra and unneeded while loop. So something like

ifconfig | perl -ne 'print if /...../'

Upvotes: 1

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