Works in bash

Change to for dash

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defining functions

function f(){echo hello world}

f() { echo hello world ; }

"function" is not defined by posix, only "name ()" is

case

;;& ;& etc

none. duplicate the case (use a funnction to avoid code duplication)

;;& ;& in bash4 is not defined by posix

numeric C-like for loop

for ((i=0; i<3; i++)); do echo $i ; done

i=0 ; while test $i -lt 3 ; do echo $i ; i=$(($i+1)) ; done

this syntax is not defined by posix

expand sequences

echo $'hello\tworld'

printf "hello\tworld"

$' ' is not defined by posix

extended glob

+( ) @( ) !( ) *( )

not always possible, some times you can use several globs, sometimes you can use find(1)

not defined by posix

select

select

some ideas: implement the menu yourself, use a command like dialog

select is not defined by posix

Works in bash

Change to for dash

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simple test

[[

use [ and use double quotes around the expansions [ "$var" = "" ]

[[ is not defined by posix

pattern matching

[[ foo = *glov ]]

use case or grep

see BashFAQ/041

equality with test

==

use = instead

only = is defined by posix, = works also in bash

compare lexicographically.

< >

no change

works with dash but not defined by posix a possible workaround with awk: awk -v v1="1" -v v2="fcd" 'BEGIN{exit !(v1 "" < "" v2)}'

compare modification times

[[ file1  -nt file2 ]] or -ot`

[ "$(find 'file1' -prune -newer 'file2')" ]

-prune is required to avoid recursion

check if 2 files are the same hardlink

[[  file1 -ef file2 ]]

?

-et is not defined by posix

(( ))

(( )) (without the $) acts like a command on its own

For simple comparison: [ -lt ] (and -ne -gt -ge) or [ "$(( 3+1 < 5))" -eq 0 ].

To assign a variable var=$((3+1))

Works in bash

Change to for dash

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keep track of the times

SECONDS

before=$(date +%s) ....seconds=$(( $(date +%s) - $before))

date +%s is not posix see this faq for more info

Generate a random number

RANDOM

random=$(awk 'BEGIN{srand(); printf "%d\n",(rand*256)}') gives a number between 0 and 256

Be sure to learn what srand() and rand() do, ie this method fails if you call awk several times rapidly. Instead generate all the numbers you need inside awk. Some systems also provides /dev/random and /dev/urandom

Get the status of all the commands in a pipeline

PIPESTATUS

Simplest solution mkfifo fifo; command2 <fifo & command1 >fifo; echo $? see NamedPipes

see this faq and this script pipe status for posix shell