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Q&A A shell script that can run under different shells

I came up with three methods. Exit early Use exit early instead of the elif syntax. Basically shell is an interpreter. As soon as the parsing of the first if statement is finished, it will be e...

posted 2y ago by mjy‭

Answer
#1: Initial revision by user avatar mjy‭ · 2022-03-18T18:09:53Z (about 2 years ago)
I came up with three methods.


### Exit early

Use `exit` early instead of the `elif` syntax.
Basically shell is an interpreter.
As soon as the parsing of the first `if` statement is finished, it will be executed.
In this case, if shell is bash, `exit` before the parsing of the next `if` statement begins. 

```sh
if [ -n "$BASH_VERSION" ]; then
    for f in *; do echo __BASH__ $f; done
    exit
fi

if [ -n "$ZSH_VERSION" ]; then
    for f (*) echo __ZSH__ $f
fi
```


### Eval string

Use `eval`.

```sh
if [ -n "$BASH_VERSION" ]; then
    for f in *; do echo __BASH__ "$f"; done
elif [ -n "$ZSH_VERSION" ]; then
    eval 'for f (*) echo __ZSH__ "$f"'
fi
```


### Source here-document

This is the same as [Canina's answer](https://linux.codidact.com/posts/285278/285301#answer-285301). However, you can write the code in the same file by using here-document. 

```sh
if [ -n "$BASH_VERSION" ]; then
    for f in *; do echo __BASH__ "$f"; done
elif [ -n "$ZSH_VERSION" ]; then
    source /dev/stdin << '__ZSH_SRC__'
        for f (*) echo __ZSH__ "$f"
__ZSH_SRC__
fi
```