shGetting started with sh

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sh is not a single shell. Rather, it is a specification with the POSIX operating system standard for how a shell should work. A script that targets this specification can be executed by any POSIX-compliant shell, such as

  • bash
  • ksh
  • ash and its derivatives, such as dash
  • zsh

In a POSIX-compliant operating system, the path /bin/sh refers to a POSIX-compliant shell. This is usually a shell that has features not found in the POSIX standard, but when run as sh, will restrict itself to the POSIX-compliant subset of its features.


Echo Portability

$ for shell in ash bash dash ksh ksh93 zsh; do
>     $shell -c "echo '\\\\'$shell'\\\\'"
> done

'echo' can only be used consistently, across implementations, if its arguments do not contain any backslashes (reverse-solidi), and if the first argument does not start with a dash (hyphen-minus). Many implementations allow additional options, such as -e , even though the only option allowed is -n (see below).


If the first operand is -n, or if any of the operands contain a character, the results are implementation-defined.

Hello, world!

With echo :

$ echo Hello, world!
Hello, world!

With printf :

$ printf 'Hello, world!\n'
Hello, world!

As a file:

printf '%s\n' 'Hello, world!'
Arithmetic Expansion