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I would like to keep the lines with exactly 639 characters in my .txt file. What is the command to do so?

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4 Answers 4

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16

You can use grep:

grep -E '^.{639}$' your.txt

The ^ and $ match beginning and end of line. The .{639} match any character exactly 639 times.

As Stéphane commented, this can be shortened (by one character) to:

grep -Ex '.{639}' your.txt

with -x indicating: Select only those matches that exactly match the whole line

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    @Student If this solves your problem, please consider accepting this answer by clicking the ✔ (checkmark) next to the answer. That is the way other people know your problem has been solved. If a better answer comes along, you can always change the accepted answer.
    – Anthon
    Apr 18, 2016 at 11:28
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    Or just grep -Ex '.{639}'
    – Stéphane Chazelas
    Apr 18, 2016 at 13:49
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    Never bury in obscure, tool dependant options what can be expressed in standard language features.
    – simpleuser
    Apr 18, 2016 at 22:08
  • @user1663987, -x is specified in POSIX; if that's "obscure" to you, you would be well advised to study through the entirety of man man and learn to use it. ;)
    – Wildcard
    Apr 19, 2016 at 8:07
  • It can be obscure if it is a seldom used option which implements commonly known operators.
    – simpleuser
    Apr 19, 2016 at 13:10
12

using awk:

awk 'length == 639'

or slightly more understandable:

awk 'length() == 639'

\thanks{@fedorqui}

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    From man awk: There is one feature of historical AWK implementations that gawk supports: It is possible to call the length() built-in function not only with no argument, but even without parentheses! But then, Using this feature is poor practice, and gawk issues a warning about its use if --lint is specified on the command line. Even though it works, to me, this is quite misleading.
    – fedorqui
    Apr 18, 2016 at 14:05
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    perhaps awk 'length() == 639' ?
    – JJoao
    Apr 18, 2016 at 14:24
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    To me, this is way more understandable : )
    – fedorqui
    Apr 18, 2016 at 14:27
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You can use Vim in Ex mode:

ex -sc 'v/\v^.{639}$/d' -cx file.txt

  1. \v turn on magic

  2. ^.{639}$ find lines of exactly 639 characters

  3. v invert selection

  4. d delete

  5. x save and close

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-1

You haven't said what your data is, or whether its acceptable to break up words in the middle. So here's an alternative that may suit written text better.

export MANWIDTH=639
cat file.txt | man -l -

This will use your default pager to display, or you pipe the output to something else.

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