Replace substring in shell script

Question

I have a string "st xxx street st st" and i want to change to "street xxx street street street". I can replace middle st, but how can i replace others. Here is my code so far:

#!/bin/bash

SPACE=" "
input="st xxx street st st"
search_string="st"
replace_string="street"
output=${input//$SPACE$search_string$SPACE/$SPACE$replace_string$SPACE}

Why don't you use sed/awk etc.? With bash sth like while [[ $input =~ (^|.* )st( .*|$) ]]; do input="${BASH_REMATCH[1]}street${BASH_REMATCH[2]}"; done; echo "$input" would work but it's too much work — oguz ismail
– oguz ismail, Commented Feb 27, 2020 at 12:33
@UmarAmin, Then as already suggested by oguz ismail try using sed or awk solutions, I think sed one is already posted. — RavinderSingh13
– RavinderSingh13, Commented Feb 27, 2020 at 12:43
@RavinderSingh13 thanks fam, but a solution with sed/awk is what OP exactly needs and I don't want to distract from that — oguz ismail
– oguz ismail, Commented Feb 27, 2020 at 13:03

oguz ismail · Accepted Answer · 2020-02-27 12:37:49Z

3

Try using sed if that is possible:

echo "$input" | sed 's/\bst\b/street/g'

\b in GNU sed refers to word boundaries.

Also refer: How can I find and replace only if a match forms a whole word?

edited Feb 27, 2020 at 12:37

oguz ismail

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answered Feb 27, 2020 at 12:36

Fazlin

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Comments

Benjamin W. · Accepted Answer · 2020-02-27 14:29:16Z

2

I'm assuming that there are never any occurrences of street at line beginning or end.

I suggest you try this:

Make all street occurrences to st:

output=${input//$SPACE$replace_string$SPACE/$SPACE$search_string$SPACE}

Now you can safely change st to street without the spaces:
```
output2=${output//$search_string/$replace_string}
```

edited Feb 27, 2020 at 14:29

Benjamin W.

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answered Feb 27, 2020 at 13:10

Markante Makrele

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Comments

user12938074 · Accepted Answer · 2020-02-27 13:22:49Z

0

I have tried a 'simple-stupid' procedure, in which I first change all spaces to newlines, then search for (temporary) lines containing just 'st', which I change to street, and I revert the newlines back in the end.

input='anst xxx street st st'
echo "$input" | sed 's/ /\n/g' | sed 's/^st$/street/g' | tr '\n' ' ' | sed 's/ $/\n/'

output:

anst xxx street street street

Words only containing st shall not be substitued.

answered Feb 27, 2020 at 13:22

user12938074

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Comments

Ivan · Accepted Answer · 2020-02-27 13:32:07Z

0

Add this two

output=${output//$search_string$SPACE/$replace_string$SPACE}
output=${output//$SPACE$search_string/$SPACE$replace_string}

Update on comment, then with help of |

output="|${input//$SPACE$search_string$SPACE/$SPACE$replace_string$SPACE}|"
output=${output//"|$search_string$SPACE"/$replace_string$SPACE}
output=${output//"$SPACE$search_string|"/$SPACE$replace_string}
output=${output//|}

Or like Markante Makrele suggested

output=${input//$replace_string/$search_string}
output=${output//$search_string/$replace_string}

But better use sed.

edited Feb 27, 2020 at 13:32

answered Feb 27, 2020 at 12:10

Ivan

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1 Comment

Umar Amin Over a year ago

second one will not work because " street" will be replaced with "streetreet"

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