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

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

Answer 2

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 is to use the read builtin.

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

Answer 3

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')

Answer 4

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 ("$@").

---

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.

---

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.

For shells that have arrays may be as simple as:
(tested working in attsh, lksh, mksh, ksh, and bash)

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

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.

Answer 5

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

elements=(${(s:_:)string})

and then access each/any element via array index:

print -r ${elements[4]}

Keep in mind that in zsh (unlike ksh/bash) array indices start at 1.

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

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=`echo ${this_str} | awk -F_ '{print $1}'`
B=`echo ${this_str} | awk -F_ '{print $2}'`
C=`echo ${this_str} | awk -F_ '{print $3}'`
... and so on...