How to truncate long matching lines returned by grep or ack

Question

I want to run ack or grep on HTML files that often have very long lines. I don\'t want to see very long lines that wrap repeatedly. But I do want to see just that portion of

Answer 1

Taken from: http://www.topbug.net/blog/2016/08/18/truncate-long-matching-lines-of-grep-a-solution-that-preserves-color/

The suggested approach ".{0,10}<original pattern>.{0,10}" is perfectly good except for that the highlighting color is often messed up. I've created a script with a similar output but the color is also preserved:

#!/bin/bash

# Usage:
#   grepl PATTERN [FILE]

# how many characters around the searching keyword should be shown?
context_length=10

# What is the length of the control character for the color before and after the
# matching string?
# This is mostly determined by the environmental variable GREP_COLORS.
control_length_before=$(($(echo a | grep --color=always a | cut -d a -f '1' | wc -c)-1))
control_length_after=$(($(echo a | grep --color=always a | cut -d a -f '2' | wc -c)-1))

grep -E --color=always "$1" $2 |
grep --color=none -oE \
    ".{0,$(($control_length_before + $context_length))}$1.{0,$(($control_length_after + $context_length))}"

Assuming the script is saved as grepl, then grepl pattern file_with_long_lines should display the matching lines but with only 10 characters around the matching string.

Answer 2

cut -c 1-100

gets characters from 1 to 100.

Answer 3

In the unusual situation where you cannot use -E, you can use:

grep -oe ".\{0,10\}error.\{0,10\}" mylogfile.txt

Answer 4

Pipe your results thru cut. I'm also considering adding a --cut switch so you could say --cut=80 and only get 80 columns.

Answer 5

You could use less as a pager for ack and chop long lines: ack --pager="less -S" This retains the long line but leaves it on one line instead of wrapping. To see more of the line, scroll left/right in less with the arrow keys.

I have the following alias setup for ack to do this:

alias ick='ack -i --pager="less -R -S"' 

Answer 6

Here's what I do:

function grep () {
  tput rmam;
  command grep "$@";
  tput smam;
}

In my .bash_profile, I override grep so that it automatically runs tput rmam before and tput smam after, which disabled wrapping and then re-enables it.