How to extract the value 2 from b="a=2" and assign it to variable a in Bash

Question

Just a stupid question. Provide a code snippet

b="a=2"

How to extract the value 2 and assign it to variable a

Huh? Do you want a bash script to do that, or a compiled program? — wallyk, Jan 11 '12 at 07:21

score 3 · Answer 1 · answered Jan 11 '12 at 07:30

3

You could just eval the code..

eval $b

answered Jan 11 '12 at 07:30

Geoffrey

1

Until somebody does `b="rm -rf /;a=2"`. As the saying goes *if eval is the answer, you're asking the wrong question* – SiegeX Jan 11 '12 at 07:39
@SergeX - Very true, but not an issue if its not a field that a an argument is used in (trusted). – Geoffrey Jan 11 '12 at 07:41

jaypal singh · Answer 2 · 2012-01-11T08:05:00.710

3

I am renowned to give ugly solutions so I won't dissapoint you -

[jaypal:~/Temp] a=$(awk '{print $(NF-1)}' FS='["=]' <<< 'b="a=2"')
[jaypal:~/Temp] echo $a
2

Less intense solution

[jaypal:~/Temp] a=$(awk -F= '{print $NF}' <<< $b)
[jaypal:~/Temp] echo $a
2

edited Jan 11 '12 at 08:05

answered Jan 11 '12 at 07:31

jaypal singh

1

You might get your P.R. person to rebrand your work as *intense and portable* rather than *ugly*. :-) – wallyk Jan 11 '12 at 07:42
+1 for an *intense and portable* answer ;) Although you could make it slightly less intense if you use single quotes for `FS` so you don't have to escape the double-quote and set `FS` at the end so you don't need `-v` `a=$(awk '{print $(NF-1)}' FS='["=]' <<< 'b="a=2"';)` – SiegeX Jan 11 '12 at 08:03
Thanks @SiegeX .. have updated the answer... There is a `less intense` solution too for the faint hearted. I am on a run with 20 solutions getting 28 up-votes with **no accepted** answer. I wonder why? :) – jaypal singh Jan 11 '12 at 08:08

score 2 · Accepted Answer · answered Jan 11 '12 at 07:22

2

a=${b#a=}

Take the value of $b, remove the leading text a=; assign what's left (2) to a.

answered Jan 11 '12 at 07:22

Jonathan Leffler

score 2 · Answer 4 · answered Jan 11 '12 at 07:23

2

$ b="a=2"
$ var=${b##*=}; echo $var
2

answered Jan 11 '12 at 07:23

SiegeX

He wanted his variable called `a`, not `var` :) – Jonathan Leffler Jan 11 '12 at 07:24
@JonathanLeffler I can't wait until I get the crystalball perk when I hit 100K rep =) – SiegeX Jan 11 '12 at 07:31
@SiegeX or you and I can combine forces and downvote Jon's every answer till date and bring him under 100k :P – jaypal singh Jan 11 '12 at 07:35

score 1 · Answer 5 · edited May 23 '17 at 10:24

1

If you are looking for a shell utility to do something like that, you can use the cut command.

To take your example, try:

echo "abcdefg" | cut -c3-5

Where -cN-M tells the cut command to return columns N to M, inclusive.

edited May 23 '17 at 10:24

Community

answered Jan 11 '12 at 07:23

Using `cut` is a heavy-duty way to do it given that the shell has built-in functionality that can do it. With `bash` and still using `cut`, you could save on a pipe using `a=$(cut -c3 <<< $b)`. For other ways to do it, see the other answers. – Jonathan Leffler Jan 11 '12 at 07:28
you can also check this.. I googled http://ask.metafilter.com/80862/how-split-a-string-in-bash – Manish Shrivastava Jan 11 '12 at 07:29

score 1 · Answer 6 · answered Jan 11 '12 at 12:03

1

another portable solution

IFS='='
set -- $b
let "$1=$2"

answered Jan 11 '12 at 12:03

glenn jackman

6 Answers6