Ubuntu – Convert seconds since epoch to a human readable string

If the string is already stored in a variable you can use bash's parameter expansion, specifially ${parameter,,pattern} (available since bash 4.0), where parameter is the name of your variable and pattern is ommitted:

$ string="Hello, World!"
$ echo $string
Hello, World!
$ echo ${string,,}
hello, world!

Note that this does not change the value of the variable, only the output. To change the variable you have to assign the new value:

$ echo $string
Hello, World!
$ string=${string,,}
$ echo $string
hello, world!

The upper-case conversion works with ${parameter^^pattern}:

$ echo ${string^^}
HELLO, WORLD!

This works also with Unicode strings (at least with current bash versions, probably needs at least bash 4.3):

$ string='ἈΛΦΆβητος'
$ echo ${string,,}
ἀλφάβητος
$ echo ${string^^}
ἈΛΦΆΒΗΤΟΣ

If you are using zsh, you can use Parameter Expansion Flags (${(FLAGS)NAME}; available since zsh 2.5) to achieve the same results. The bash syntax does not work in zsh ¹⁾. The flag for lower case is L; for upper case it is U:

$ string="Hello, World!"
$ echo ${(L)string}
hello, world!
$ echo ${(U)string}
HELLO, WORLD!
$ echo $string
Hello, World!"

This also works with Unicode strings (at least since zsh 5.0; I did not try with earlier versions):

$ string='ἈΛΦΆβητος'
$ echo ${(L)string} 
ἀλφάβητος
$ echo ${(U)string}  
ἈΛΦΆΒΗΤΟΣ

¹⁾ Although, seeing that zsh had this for far longer, it should probably be: "the zsh syntax does not work in bash.

First, you need to remove the text from around the assignment of the string variable:

text="'xdc','cde','erd','ded','ded','kie';"

Then you can just use the array form of the bash read command:

IFS=, read -a ids <<< "${text%;}"

where the ${text%;} substitution removes the trailing semicolon. Note that, this way, the IFS is not modified outside of the read command so there's no need to save and restore it.

Your C-style for-loop syntax is almost correct, except that in bash, the loop needs double parentheses e.g.

for ((i=0; i<${#ids[@]}; ++i)); do printf '%s\n' "${ids[i]}"; done

Alternatively, you can loop over array members directly using a for ... in loop:

for i in "${ids[@]}"; do printf '%s\n' "$i"; done