Split string by delimiter and get N-th element

Question

I have a string:

one_two_three_four_five

I need to save in a variable A value two and in variable B value fourfrom the above string

I am using ksh.

Answer 1

Use cut with _ as the field delimiter and get desired fields:

A="$(cut -d'_' -f2 <<<'one_two_three_four_five')"
B="$(cut -d'_' -f4 <<<'one_two_three_four_five')"

You can also use echo and pipe instead of Here string:

A="$(echo 'one_two_three_four_five' | cut -d'_' -f2)"
B="$(echo 'one_two_three_four_five' | cut -d'_' -f4)"

Example:

$ s='one_two_three_four_five'

$ A="$(cut -d'_' -f2 <<<"$s")"
$ echo "$A"
two

$ B="$(cut -d'_' -f4 <<<"$s")"
$ echo "$B"
four

Beware that if $s contains newline characters, that will return a multiline string that contains the 2^nd/4^th field in each line of $s, not the 2^nd/4^th field in $s.

Answer 2

Wanted to see an awk answer, so here's one:

A=$(awk -F_ '{print $2}' <<< 'one_two_three_four_five')
B=$(awk -F_ '{print $4}' <<< 'one_two_three_four_five')  

Try it online!

Answer 3

Using only POSIX sh constructs, you can use parameter substitution constructs to parse one delimiter at a time. Note that this code assumes that there is the requisite number of fields, otherwise the last field is repeated.

string='one_two_three_four_five'
remainder="$string"
first="${remainder%%_*}"; remainder="${remainder#*_}"
second="${remainder%%_*}"; remainder="${remainder#*_}"
third="${remainder%%_*}"; remainder="${remainder#*_}"
fourth="${remainder%%_*}"; remainder="${remainder#*_}"

Alternatively, you can use an unquoted parameter substitution with wildcard expansion disabled and IFS set to the delimiter character (this only works if the delimiter is a single non-whitespace character or if any whitespace sequence is a delimiter).

string='one_two_three_four_five'
set -f; IFS='_'
set -- $string
second=$2; fourth=$4
set +f; unset IFS

This clobbers the positional parameters. If you do this in a function, only the function's positional parameters are affected.

Yet another approach for strings that don't contain newline characters is to use the read builtin.

IFS=_ read -r first second third fourth trail <<'EOF'
one_two_three_four_five
EOF

Answer 4

Here string

The simplest way (for shells with <<<) is:

 IFS='_' read -r a second a fourth a <<<"$string"

Using a temporal variable $a instead of $_ because one shell complains.

In a full script:

 string='one_two_three_four_five'
 IFS='_' read -r a second a fourth a <<<"$string"
 echo "$second $fourth"

No IFS changing, not issues with set -f (Pathname expansion) No changes to the positional parameters ("$@").

---

Heredoc
For a solution portable to all shells (yes, all POSIX included) without changing IFS or set -f, use the (a bit more complex) heredoc equivalent:

string='one_two_three_four_five'

IFS='_' read -r a second a fourth a <<-_EOF_
$string
_EOF_

echo "$second $fourth"

Understand that this solutions (both the here-doc and the use of <<< will remove all trailing newlines.
And that this is designed to a "one liner" variable content.
Solutions for multi-liners are possible but need more complex constructs.

---

Bash 4.4+
A very simple solution is possible in bash version 4.4

readarray -d _ -t arr <<<"$string"

echo "array ${arr[1]} ${arr[3]}"   # array numbers are zero based.

There is no equivalent for POSIX shells, as many POSIX shells do not have arrays.

Arrays
For shells that have arrays may be as simple as:
(tested working in attsh, lksh, mksh, ksh, and bash (not zsh))

set -f; IFS=_; arr=($string)

But with a lot of additional plumbing to keep and reset variables and options:

string='one_* *_three_four_five'

case $- in
    *f*) noglobset=true; ;;
    *) noglobset=false;;
esac

oldIFS="$IFS"

set -f; IFS=_; arr=($string)

if $noglobset; then set -f; else set +f; fi

IFS=$oldIFS

echo "two=${arr[1]} four=${arr[3]}"

In zsh, arrays start in 1, and doesn't split string by default.
So some changes need to be done to get this working in zsh:

set -F; IFS=_; arr=( $(echo $string) )
echo "two=${arr[2]} four=${arr[4]}"

Answer 5

With zsh you could split the string (on _) into an array:

non_empty_elements=(${(s:_:)string})
all_elements=("${(@s:_:)string}")

and then access each/any element via array index:

print -r -- ${all_elements[4]}

Keep in mind that in zsh (like most other shells, but unlike ksh/bash) array indices start at 1.

Or directly in one expansion:

print -r -- "${${(@s:_:)string}[4]}"

Answer 6

Is a python solution allowed?

# python -c "import sys; print sys.argv[1].split('_')[1]" one_two_three_four_five
two

# python -c "import sys; print sys.argv[1].split('_')[3]" one_two_three_four_five
four

Answer 7

With due respect to everyone who have posted excellent answers, I wonder if we are over-engineering this problem. Three simple lines to just answer the question asked without generalizing:

str="one_two_three_four_five" <-- create a string

A=$(echo $str | awk -F_ '{print $2}') <-- tell awk to use _ as the delimiter and assign the second field to A

B=$(echo $str | awk -F_ '{print $4}') <-- tell awk to use _ as the delimiter and assign the fourth field to B

You can then use the variables as usual. Here is an example:

$ echo "The value of A is: $A; the value of B is: $B"
The value of A is: two; the value of B is: four
$ 

Answer 8

Another awk example; simpler to understand.

A=$(echo one_two_three_four_five | awk -F_ '{print $1}')
B=$(echo one_two_three_four_five | awk -F_ '{print $2}')  
C=$(echo one_two_three_four_five | awk -F_ '{print $3}')  
... and so on...  

Can be used with variables also.

Suppose:

this_str="one_two_three_four_five"  

Then the following works:

A=$(printf '%s\n' "${this_str}" | awk -F_ '{print $1}')
B=$(printf '%s\n' "${this_str}" | awk -F_ '{print $2}')
C=$(printf '%s\n' "${this_str}" | awk -F_ '{print $3}')
... and so on...  

That assumes ${this_str} doesn't contain newline characters, or it would return the first _ in each line of the contents of the variable instead of the first field in the contents of the variable.