I would like to know the following;
Non-working example
> ids=(1 2 3 4);echo ${ids[*]// /|}
1 2 3 4
> ids=(1 2 3 4);echo ${${ids[*]}// /|}
-bash: ${${ids[*]}// /|}: bad substitution
> ids=(1 2 3 4);echo ${"${ids[*]}"// /|}
-bash: ${"${ids[*]}"// /|}: bad substitution
Working example
> ids=(1 2 3 4);id="${ids[@]}";echo ${id// /|}
1|2|3|4
> ids=(1 2 3 4); lst=$( IFS='|'; echo "${ids[*]}" ); echo $lst
1|2|3|4
In context, the delimited string to be used in a sed command for further parsing.
bash$IFSBecause parentheses are used to delimit an array, not a string:
ids="1 2 3 4";echo ${ids// /|}
1|2|3|4
Some samples: Populating $ids with two strings: a b and c d
ids=("a b" "c d" e\ f)
echo ${ids[*]// /|}
a|b c|d e|f
IFS='|';echo "${ids[*]}";IFS=$' \t\n'
a b|c d|e f
... and finally:
IFS='|';echo "${ids[*]// /|}";IFS=$' \t\n'
a|b|c|d|e|f
Where array is assembled, separated by 1st char of $IFS, but with space replaced by | in each element of array.
When you do:
id="${ids[@]}"
you transfer the string build from the merging of the array ids by a space to a new variable of type string.
Note: when "${ids[@]}" give a space-separated string, "${ids[*]}" (with a star * instead of the at sign @) will render a string separated by the first character of $IFS.
what man bash says:
man -Len -Pcol\ -b bash | sed -ne '/^ *IFS /{N;N;p;q}'
IFS The Internal Field Separator that is used for word splitting
after expansion and to split lines into words with the read
builtin command. The default value is ``<space><tab><newline>''.
Playing with $IFS:
printf "%q\n" "$IFS"
$' \t\n'
Literally a space, a tabulation and (meaning or) a line-feed. So, while the first character is a space. the use of * will do the same as @.
But:
{
IFS=: read -a array < <(echo root:x:0:0:root:/root:/bin/bash)
echo 1 "${array[@]}"
echo 2 "${array[*]}"
OIFS="$IFS" IFS=:
echo 3 "${array[@]}"
echo 4 "${array[*]}"
IFS="$OIFS"
}
1 root x 0 0 root /root /bin/bash
2 root x 0 0 root /root /bin/bash
3 root x 0 0 root /root /bin/bash
4 root:x:0:0:root:/root:/bin/bash
Note: The line IFS=: read -a array < <(...) will use : as separator, without setting $IFS permanently. This is because output line #2 present spaces as separators.
$IFSTo just print array
printArry() {
local IFS="$1"
shift
echo "$*"
}
printArry @ "${ids[@]}"
a b@c d@e f
Or to merge array in place.
mergeArry() {
local IFS="$1"
local -n _array_to_merge=$2
_array_to_merge=("${_array_to_merge[*]}")
}
declare -p ids
declare -a ids=([0]="a b" [1]="c d" [2]="e f")
mergeArry '#' ids
declare -p ids
declare -a ids=([0]="a b#c d#e f")
[@] vs [*])There is a notable difference between:
"$@" and "${var[@]}" result in an array of strings"$*" and "${var[*]}" result in an unique stringRead carefully: man '-Pless +/Special\ Parameters' bash
For this, I will quote each argument in order to not be splitted by $IFS at command line expansion, using double-quotes to permit variable expansion.
ids=('a b c' 'd e f' 'g h i')
printf '<< %s >>\n' "${ids[@]// /|}"
<< a|b|c >>
<< d|e|f >>
<< g|h|i >>
printf '<< %s >>\n' "${ids[*]// /|}"
<< a|b|c d|e|f g|h|i >>
Where:
$IFS character.( IFS='@'; printf '<< %s >>\n' "${ids[*]// /|}" )
<< a|b|c@d|e|f@g|h|i >>
Note: ${var// /something} will replace every spaces by something, but ${var[*]} will merge array by using only one 1st character:
( IFS='FOO'; printf '<< %s >>\n' "${ids[*]// / BAR }" )
<< a BAR b BAR cFd BAR e BAR fFg BAR h BAR i >>
And yes: by using ${var// / ... }, you could replace 1 space by anthing you want, including more spaces.
printfAs we see, using $IFS is limited to only 1 character. If you need to use more characters to be inserted between your fields. You have to use printf:
ids=("a b" "c d" e\ f)
sep=" long separator "
printf -v string "%s$sep" "${ids[@]}"
echo "${string%$sep}"
a b long separator c d long separator e f
Note: this syntax work but is something limited, see further!
printf, into a functionIn order to support special characters as % or * in separator, the function have to prevents
% to be interpreted by printf (printf '%%' will render a %) and* to be interpreted by parameter expansion, for this $sep have to be double quoted.printArry() {
local sep=$1 string
shift
printf -v string "%s${sep//%/%%}" "$@"
echo "${string%"$sep"}"
}
printArry ' long separator ' "${ids[@]}"
a b long separator c d long separator e f
printArry '*' "${ids[@]}"
a b*c d*e f
printArry '%' "${ids[@]}"
a b%c d%e f
Or to merge array in place.
mergeArry() {
local sep=$1 string
local -n _array_to_merge=$2
printf -v string "%s${sep//%/%%}" "${_array_to_merge[@]}"
_array_to_merge=("${string%"$sep"}")
}
ids=("a b" "c d" e\ f)
mergeArry ' another separator ' ids
declare -p ids
declare -a ids=([0]="a b another separator c d another separator e f")
ids=("a b" "c d" e\ f)
mergeArry '*' ids
declare -p ids
declare -a ids=([0]="a b*c d*e f")
Instead of using nameref for array variable, you could use:
MergeWithSep() {
if [[ $1 == -v ]]; then local outvar=$2 sep=$3 string; shift 3
else local outvar sep=$1 string; shift
fi
printf -v string "%s${sep//%/%%}" "$@"
if [[ -n $outvar ]]; then
printf -v $outvar "%s" "${string%"$sep"}"
else
echo "${string%"$sep"}"
fi
}
ids=("a b" "c d" e\ f)
MergeWithSep ' || ' "${ids[@]}"
a b || c d || e f
MergeWithSep $'\n - ' " - "Hello\ world. 'This is a sentence.'
- Hello world.
- This is a sentence.
MergeWithSep -v var ', ' {A..Z}
echo $var.
A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z.
bash's parameter expansionYet another way TMTOWTDI: But as for working, we have to empty $IFS, I prefer to use this in a function for localize $IFS.
printArry () {
local -n _array_to_print=$2
local IFS=
local _string_to_print="${_array_to_print[*]/#/"$1"}"
echo "${_string_to_print/#"$1"}"
}
Note you could replace # by % as
$1, while$1, thenmergeArry () {
local -n _array_to_merge=$2
local IFS=
_array_to_merge=("${_array_to_merge[*]/#/"$1"}")
_array_to_merge=("${_array_to_merge/#"$1"}")
}
printArry () {
local -n _array_to_print=$2
local IFS=
local _string_to_print="${_array_to_print[*]/#/"$1"}"
echo "${_string_to_print:${#1}}"
}
mergeArry () {
local -n _array_to_merge=$2
local IFS=
_array_to_merge=("${_array_to_merge[*]/#/"$1"}")
_array_to_merge=("${_array_to_merge:${#1}}")
}
Or
printArry () {
local -n _array_to_print=$2
local IFS=
local _string_to_print="${_array_to_print[*]/%/"$1"}"
echo "${_string_to_print::-${#1}}"
}
MergeWithSep() {
if [[ $1 == -v ]]; then local outvar=$2 sep=$3 string; shift 3
else local outvar sep=$1 string; shift
fi
local IFS=
string=${@/#/"$sep"}
if [[ -n $outvar ]]; then
printf -v outvar %s "${string/#"$sep"}"
else
echo "${string/#"$sep"}"
fi
}
To do...