Bash: extract a part of a string, after a number

Question

I have a few strings like this:

var1="string one=3423423 and something which i don't care"
var2="another bigger string=413145 and something which i don't care"
var3="the longest string ever=23442 and something which i don't care"

These strings are the output of a python script (which i am not allowed to touch), and I need a way to extract the 1st part of the string, right after the number. Basically, my outputs should be:

"string one=3423423"
"another bigger string=413145"
"the longest string ever=23442"

As you can see, i can't use positions, or stuff like that, because the number and the string length are not always the same. I assume i would need to use a regex or something, but i don't really understand regexes. Can you please help with a command or something which can do this?

P.... · Accepted Answer · 2017-10-27 12:50:40Z

1

grep -oP '^.*?=\d+' inputfile
string one=3423423
another bigger string=413145
the longest string ever=23442

Here -o flag will enable grep to print only matching part and -p will enable perl regex in grep. Here \d+ means one or more digit. So, ^.*?=\d+ means print from start of the line till you find last digit (first match).

edited Oct 27, 2017 at 12:50

answered Oct 27, 2017 at 12:44

P....

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2 Comments

Renaud Pacalet Over a year ago

You should probably use a non-greedy form of your RE (^.*?=\d+) to fully comply with the OP's requirements.

David Botezatu Over a year ago

@PS. I have made a mistake in the original post: Basically i have var="string one=3423423 and something which i don't care" and i need a command, that turns that string into string one=3423423

janos · Accepted Answer · 2017-10-27 13:08:15Z

0

You could use parameter expansion, for example:

var1="string one=3423423 and something which i don't care"
name=${var1%%=*}
value=${var1#*=}
value=${value%%[^0-9]*}
echo "$name=$value"
# prints: string one=3423423

Explanation of ${var1%%=*}:

%% - remove the longest matching suffix
= - match =
* - match everything

Explanation of ${var1#*=}:

# - remove the shortest matching prefix
* - match everything
= - match =

Explanation of ${value%%[^0-9]*}:

%% - remove the longest matching suffix
[^0-9] - match any non-digit
* - match everything

To perform the same thing on more than one values easily, you could wrap this logic into a function:

extract_and_print() {
    local input=$1
    local name=${input%%=*}
    local value=${input#*=}
    value=${value%%[^0-9]*}
    echo "$name=$value"
}

extract_and_print "$var1"
extract_and_print "$var2"
extract_and_print "$var3"

edited Oct 27, 2017 at 13:08

answered Oct 27, 2017 at 12:44

janos

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7 Comments

David Botezatu Over a year ago

this works if my string would be string1="3423423 and something which i don't care" but my string is var="string one=3423423 and something which i don't care" Basically, the = is inside the string, it is not the sign for assigning something to a variable. My bad, i have to edit the 1st post :)

David Botezatu Over a year ago

I am not used with asking questions, and for a new line it seems i have to press Shift + Enter instead of just Enter. Please recheck my comment, i've edited it.

David Botezatu Over a year ago

i really am sorry for the mistake. This is my 2nd time i'm asking for help (usually i can make it on my own), and plus the fact that this is the 3rd day i'm working in Bash, so it's a bit difficult for me to ask good questions, cuz basically i don't really know what to ask :)

janos Over a year ago

@DavidBotezatu I rewrote my answer according to match your updated question.

David Botezatu Over a year ago

Thank you very much! I still have 1 more question for you: why did you do value=${var1#*=} value=${value%%[^0-9]*} instead of maybe value=${var1#*=} value2=${value%%[^0-9]*} Can you please explain? Thanks!

|

glenn jackman · Accepted Answer · 2017-10-27 14:06:07Z

0

$ shopt -s extglob

$ echo "${var1%%+([^0-9])}"
string one=3423423

$ echo "${var2%%+([^0-9])}"
another bigger string=413145

$ echo "${var3%%+([^0-9])}"
the longest string ever=23442

+([^0-9]) is an extended pattern that matches one or more non-digits.
${var%%+([^0-9])} with %%pattern will remove the longest match of that pattern from the end of the variable value.

Refs: patterns, parameter substitution

answered Oct 27, 2017 at 14:06

glenn jackman

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