Name

hl

Synopsis

Colourise and highlight text in an output stream

Usage

hl <perl6_regex> [<file>|-|< <file>|< <(<subshell expression>)]
[shell_expression|command] | hl <perl6_regex>

Environmental Variables

HL_COLOURS='<colour_spec>,<colour_spec>' # CSV spec as per Terminal::ANSIColor

Description

hl paints text regions of an output stream or file indicated by a given Perl 6 regular expressions.

This is useful when you are looking for patterns in text but would like to preserve the context around it (like grep but not suppressing any output).

hl emerges out of a hacky (unreliable) bash alias I had lying around and the need to learn some practical Perl 6.

Examples

Highlight pattern matches

The simplest use case - matching a word.

hl root /etc/passwd

Here is an example using a more advanced (albeit trite) Perl6 regular expression

hexdump /bin/cat |
  hl '<-[0\s]+[1..9a..f]> ** 2..4'

Highlight text fields

Sometimes highlighting fields helps us find anomalies

hl '<-[:]>* <?before \:|$>' /etc/passwd

Highlight blocks of text

If you need a visual aid while staring at or reading from long blocks of text

hexdump -n $((64*16)) -v -e '/1 "%02x"' -e '/64 "\n"' /dev/urandom |
  hl '. ** 8'

π maze

And here's something fun with some digits of π

perl -lne 'print for /.{64}/g' pi-100000.txt |
  tail -n 32 | 
  HL_COLOURS='244 on_120, 244 on_255' hl '<[02468]>' |
  HL_COLOURS='45 on_24'               hl '(^|<?after m>) <[13579]>+' 

See Also

• github.com/ap/hl - Aristotle Pagaltzis's version of hl in perl 5
• docs.perl6.org/language/regexes for reference on using Perl 6 Regular Expressions.
• github.com/tadzik/Terminal-ANSIColor for colour specifications that hl uses via the HL_COLOURS environmental variable.

TODO

• hl can be really slow for large amounts of input text.
• Suppress lines not matching patterns a la grep.
• Support for highlighting individual regex captures.
• Support for nested regex captures.
• Detecting 256-colour capable terminals and falling back.