Swap Strings within a line in Bash

Question

I'm parsing a document with a bash script and output different parts of it. At one point i need find and reformat text in the form of:

(foo)[X]
[Y]
(bar)[Z]

to something like:

X->foo
Y
Z->bar

Now, I'm able to grep the parts I want with RegEx, but I'm having trouble swapping the two elements in one line and handling the fact that the text in parentheses is optional. Is this even possible with a combination of sed and grep?

Thank You for your time.

janos · Accepted Answer · 2015-12-02 21:25:47Z

3

You can use sed:

sed -e 's/(\([^)]*\))\[\([^]]*\)]/\2->\1/' -e 's/\[\([^]]*\)]/\1/' file

This works for your given input example:

X->foo
Y
Z->bar

You might need to make the patterns more strict if you have more kinds of input to handle.

answered Dec 2, 2015 at 21:25

janos

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3 Comments

pietz Over a year ago

it really does. wow, seems like i still have a lot to learn about sed! could you maybe elaborate a little bit how you actually did the swapping with a simple substitute command? your code works and my problem is solved, but im having trouble completely understanding your code. thanks so much!

pietz Over a year ago

ok i think i got it, but shouldnt you escape the last " ] " in each of your substitutes?

janos Over a year ago

That's great you figured it! No need to escape the closing ] when it is outside of a [...]. (If we needed to escape, my answer wouldn't work...)

anubhava · Accepted Answer · 2015-12-02 21:10:45Z

2

You can use awk:

awk -F '[][()]+' '{print (NF>3 ? $3 "->" $2 : $2)}' file
X->foo
Y
Z->bar

answered Dec 2, 2015 at 21:10

anubhava

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2 Comments

pietz Over a year ago

your answer is the easiest to underand and yet i think ill stick with the sed solution. thank you for your time, i should really make myself familiar with awk.

anubhava Over a year ago

sed cannot do it in one pass as you can see from 2 substitute commands in janos's answer.

chepner · Accepted Answer · 2015-12-02 22:18:36Z

1

You can even do it in bash itself, although it's not pretty.

# Three capture groups:
#  1. The optional paranthesized text
#  2. The contents of the parentheses
#  3. The contents of the square brackets
regex="(\((.*)\))?\[(.*)\]"

while IFS= read -r str; do
  [[ "$str" =~ $regex ]]

  # If the 2nd array element is not empty, print -> followed by the
  # non-empty value.
  echo "${BASH_REMATCH[3]}${BASH_REMATCH[2]:+->${BASH_REMATCH[2]}}"
done < file.txt

edited Dec 2, 2015 at 22:18

answered Dec 2, 2015 at 22:05

chepner

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1 Comment

pietz Over a year ago

thanks for your effort, but i think i prefer the sed and awk methods :)

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