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Anon
Asked: 2017-01-22 13:13:06 +0800 CST

Is it possible to do a double substitution with a shell string?

  • 772

Single Substitution is easy:

string="Mark Shuttleworth"
echo ${string/a/o}

Mork Shuttleworth

is it possible though to do a double at the same time?

echo ${string/a/o string/t/g} #doesn't work, but you get the idea

Mork Shuggleworgh

Regular Expressions suffice as an answer, if it is possible using them.

Thanks

command-line

3 Answers

  1. Best Answer

    As far as I know, the only way to do it in current versions of bash is in two steps e.g.

    $ string="Mark Shuttleworth"
$ string="${string//a/o}"; echo "${string//t/g}"
Mork Shuggleworgh

    Attempts to nest substitutions result in an error:

    $ echo "${${string//a/o}//t/g}"
bash: ${${string//a/o}//t/g}: bad substitution

    Note that other shells may support such nested substitutions e.g. in zsh 5.2:

    ~ % string="Mark Shuttleworth"
~ % echo "${${string//a/o}//t/g}"
Mork Shuggleworgh

    Of course, external tools such as tr, sed, perl can do it easily

    $ sed 'y/at/og/' <<< "$string"
Mork Shuggleworgh

$ perl -pe 'tr /at/og/' <<< "$string"
Mork Shuggleworgh

$ tr at og <<< "$string"
Mork Shuggleworgh
    • 11

  2. You're substituting single letters, so just use tr:

    tr at og

    This causes each a to be replaced by o and each t to be replaced by g. With your example:

    ek@Io:~$ tr at og <<<'Mark Shuttleworth'
Mork Shuggleworgh
    • 6

  3. Try 

    echo ${string/a/o} ${string/t/g}

    I'm using my tablet, no bash to test.

    You may want to checkout using the printf command much more flexible.

    • -1