remove particular characters from a variable using bash

Question

I want to parse a variable (in my case it's development kit version) to make it dot(.) free. If version='2.3.3', desired output is 233.

I tried as below, but it requires . to be replaced with another character giving me 2_3_3. It would have been fine if tr . '' would have worked.

  1 VERSION='2.3.3' 
  2 echo "2.3.3" | tr . _

@manatwork Great, that works. You can post it as answer. Thanks — prayagupa, Dec 12 '13 at 15:04
Lot of good answers. But if I can second-guess the objective, be warned about 2.11.3 and 2.1.13... ;-) Consider adding padding zeroes to numbers. — Rmano, Dec 12 '13 at 16:06
@Rmano You mean something like `VERSION='2.30.3100'`? No matter what just `.`'s are removed with all of the answers here. — prayagupa, Dec 12 '13 at 16:13
@PrayagUpd --- I simply meant that if you will use the number after the conversion for comparisons (as to say if "is this version newer or the same") you should take care of cases like 2.11.3 and 2.1.13 --- they seems the same after dot removal, but clearly 2.11.3 is newer. Also, 2.11.3 is newer than 2.1.14, but comparing 2113 and 2114 will lead to the wrong answer. I remember a bug somewhere for this... — Rmano, Dec 12 '13 at 16:19
@Rmano Got you. But my purpose is to identify the version in my project and get the development kit of that version located somewhere in filesystem. You can go through [my bash file](https://github.com/iPrayag/gccount/blob/master/run-app.sh#L4). Thx anyway for for warn :) — prayagupa, Dec 12 '13 at 16:27
@PrayagUpd so how do you differentiate the directories for version 2.11.3 and 2.1.13? Or are you sure you have one-digit subversion ever? — Rmano, Dec 12 '13 at 16:38
@Rmano Looking over kit's history, it has [1-digit sub- version so far](http://grails.org/download). — prayagupa, Dec 12 '13 at 16:43

score 241 · Accepted Answer · edited May 29 '20 at 15:07

241

There is no need to execute an external program. bash's string manipulation can handle it (also available in ksh93 (where it comes from), zsh and recent versions of mksh, yash and busybox sh (at least)):

$ VERSION='2.3.3'
$ echo "${VERSION//.}"
233

(In those shells' manuals you can generally find this in the parameter expansion section.)

edited May 29 '20 at 15:07

Stéphane Chazelas

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answered Dec 12 '13 at 15:25

manatwork

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For further detail, the syntax of the above answer is `${string//substring/replacement}`, where apparently the lack of the final forward slash and replacement string are interpreted as *delete*. See [here](http://tldp.org/LDP/abs/html/string-manipulation.html). – sherrellbc Jan 06 '16 at 18:19
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Right, `man bash` says it clearly in the [Shell Parameter Expansion](https://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html#Shell-Parameter-Expansion) section: “`${parameter/pattern/string}` (…) If _string_ is null, matches of _pattern_ are deleted and the `/` following _pattern_ may be omitted.” – manatwork Jan 06 '16 at 18:49
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My issue was that the version number came like this `"1.0.0"` and I wanted just the number so follow what @manatwork suggested I changed in: `"${VERSIONNUM//'"'}"` however I insert even `' ' `because otherwise it wouldn't recognise the `""` like string to take off. – Alexiscanny Sep 14 '16 at 12:53
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@Alexiscanny, you mean literal `"` are present in the value? I'm afraid this counts as new question, but try to just escape the doublequote: `"${VERSIONNUM//\"}"` http://pastebin.com/3ECDtkwH – manatwork Sep 14 '16 at 13:03
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Superb!! works on `-ash` too! – Fr0zenFyr Jan 04 '17 at 11:33
@Fr0zenFyr, that would be busybox' `ash` (when built with ASH_BASH_COMPAT )even though that's a ksh feature, not bash)) . The original `ash` didn't have it and I'm not aware of any other `ash` derivative (only tried `dash` and FreeBSD `sh` though) that has it. – Stéphane Chazelas Mar 10 '17 at 12:00
Not wanting to be a OT or a killjoy, but following the intention of the above, it would be far better to ensure that the digits are separated. For instance, compare nominal versions with 2.11.1 and 2.1.12 . The above method will fail dramatically. In fact so would 3.0 vs 2.1.6 – Konchog Aug 14 '19 at 06:22
So, again if wanting to get versions - especially for comparison, it would be far better to use "sort -V" – Konchog Aug 14 '19 at 06:32

Stéphane Chazelas · Answer 2 · 2020-05-29T15:08:04.583

137

By chronological order:

tr/sed

echo "$VERSION" | tr -d .
echo "$VERSION" | sed 's/\.//g'

csh/tcsh

echo $VERSION:as/.//

POSIX shells:

set -f
IFS=.
set -- $VERSION
IFS=
echo "$*"

ksh93/zsh/mksh/bash/yash (and busybox `ash` when built with `ASH_BASH_COMPAT`)

echo "${VERSION//.}"

zsh

echo $VERSION:gs/./

edited May 29 '20 at 15:08

answered Dec 12 '13 at 15:38

Stéphane Chazelas

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tr -d deleted even single char from the set. For Ex i want to delete DCC_ from "DCC_VersionD", It deletes DCC and D. Expected output : VersionD. Actual Output : Version. sed worked like a charm. :) thanks for the post. – kayle May 21 '18 at 11:30

score 32 · Answer 3 · edited May 29 '20 at 14:21

32

In addition to the successful answers already exists. Same thing can be achieved with tr, with the --delete option.

echo "2.3.3" | tr --delete .
echo "2.3.3" | tr -d .       # for MacOS

Which will output: 233

edited May 29 '20 at 14:21

dialex

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answered Jul 14 '16 at 03:53

daz

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on macos the `--delete` flag is not recognised, but you can use `-d` instead – Anentropic Apr 05 '18 at 17:40

score 10 · Answer 4 · edited Nov 09 '22 at 01:02

10

You should try with sed instead

sed 's/\.//g'

edited Nov 09 '22 at 01:02

Pablo A

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answered Dec 12 '13 at 14:57

fduff

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A POSIX compliant one liner, nice. – Martin Braun Feb 23 '23 at 18:55

score 7 · Answer 5 · answered Mar 16 '17 at 09:32

7

echo "$VERSION" | tr -cd [:digit:]

That would return only digits, no matter what other characters are present

answered Mar 16 '17 at 09:32

user2796674

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Only if there's no file called `:`, `d`, `i`, `g` or `t` in the current directory and you're using a shell that doesn't complain upon non-matching globs and leaves them asis (most Bourne-like ones and rc-like ones) or a shell that doesn't support `[...]` globs (like `fish`). – Stéphane Chazelas May 29 '20 at 15:17

score 5 · Answer 6 · edited Nov 15 '18 at 13:44

Perl

$ VERSION='2.3.3'                                     
$ perl -pe 's/\.//g' <<< "$VERSION"           
233

Python

$ VERSION='2.3.3'                                     
$ python -c 'import sys;print sys.argv[1].replace(".","")' "$VERSION"
233

If $VERSION only contains digits and dots, we can do something even shorter:

$ python -c 'print "'$VERSION'".replace(".","")'
233

(beware it's a code injection vulnerability though if $VERSION may contain any character).

AWK

$ VERSION='2.3.3'
$ awk 'BEGIN{gsub(/\./,"",ARGV[1]);print ARGV[1]}' "$VERSION"
233

Or this:

$ awk '{gsub(/\./,"")}1' <<< "$VERSION"
233

remove particular characters from a variable using bash

6 Answers6

tr/sed

csh/tcsh

POSIX shells:

ksh93/zsh/mksh/bash/yash (and busybox `ash` when built with `ASH_BASH_COMPAT`)

zsh

Perl

Python

AWK

Linked

remove particular characters from a variable using bash

6 Answers6

tr/sed

csh/tcsh

POSIX shells:

ksh93/zsh/mksh/bash/yash (and busybox ash when built with ASH_BASH_COMPAT)

zsh

Perl

Python

AWK

Linked

ksh93/zsh/mksh/bash/yash (and busybox `ash` when built with `ASH_BASH_COMPAT`)