sed: remove all characters except for last n characters

Question

I am trying to remove every character in a text string except for the remaining 11 characters. The string is Sample Text_that-would$normally~be,here--pe_-l4_mBY and what I want to end up with is just -pe_-l4_mBY.

Here's what I've tried:

$ cat food
Sample Text_that-would$normally~be,here--pe_-l4_mBY
$ cat food | sed 's/^.*(.{3})$/\1/'
sed: 1: "s/^.*(.{3})$/\1/": \1 not defined in the RE

Please note that the text string isn't really stored in a file, I just used cat food as an example.

OS is macOS High Sierra 10.13.6 and bash version is 3.2.57(1)-release

Improved example, didn't realise i put 10 characters instead of 11 :-/ — leetbacoon, Feb 11 '19 at 16:01
Use `cat food | sed 's/^.*$.\{11\}$$/\1/'` if you need a BRE POSIX pattern. — Wiktor Stribiżew, Feb 11 '19 at 16:14

score 5 · Accepted Answer · answered Feb 11 '19 at 15:59

5

You can use this sed with a capture group:

sed -E 's/.*(.{11})$/\1/' file

-pe_-l4_mBY

answered Feb 11 '19 at 15:59

anubhava

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score 3 · Answer 2 · answered Feb 11 '19 at 16:16

Basic regular expressions (used by default by sed) require both the parentheses in the capture group and the braces in the brace expression to be escaped. ( and { are otherwise treated as literal characters to be matched.

$ cat food | sed 's/^.*\(.\{3\}\)$/\1/'
mBY

By contrast, explicitly requesting sed to use extended regular expressions with the -E option reverses the meaning, with \( and \{ being the literal characters.

$ cat food | sed -E 's/^.*(.{3})$/\1/'
mBY

tripleee · Answer 3 · 2019-02-11T16:28:59.360

2

Try this also:

grep -o -E '.{11}$' food

grep, like sed, accepts an arbitrary number of file name arguments, so there is no need for a separate cat. (See also useless use of cat.)

edited Feb 11 '19 at 16:28

answered Feb 11 '19 at 16:25

tripleee

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score 1 · Answer 4 · answered Feb 11 '19 at 16:48

1

You can use tail or Parameter Expansion :

string='Sample Text_that-would$normally~be,here--pe_-l4_mBY'
echo "$string" | tail -c 11
echo "${string#${string%??????????}}"

pe_-l4_mBY
pe_-l4_mBY

answered Feb 11 '19 at 16:48

ctac_

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score -1 · Answer 5 · edited Jun 07 '20 at 10:57

-1

also with rev/cut/rev

$ echo abcdefghijklmnopqrstuvwxyz | rev | cut -c1-11 | rev 

pqrstuvwxyz

man rev => rev - reverse lines characterwise

edited Jun 07 '20 at 10:57

hoijui

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answered Feb 11 '19 at 16:05

karakfa

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sed: remove all characters except for last n characters

5 Answers5